Blood tests for patients on low carb

This guide provides a description of recommended lab tests that can help you monitor your patient’s progress on a low-carb diet. This is not meant to be a prescriptive list, but more of a guide to help your thought process of how to best follow patients embarking on a low-carb lifestyle.

As you go through this guide, keep in mind that many of the normal reference ranges were developed on populations eating a high carb diet, and therefore in some cases you may need to adjust your concept of normal for a patient following a low-carb lifestyle. In addition, many normal values vary based on the individual lab, the patients gender, size, etc. We try to clarify where these caveats are most important.

Alanine aminotransferase (ALT)

ALT is a liver enzyme test measuring hepatocellular damage. It can often be elevated in metabolic syndrome and obesity most commonly due to non-alcoholic fatty liver disease (NAFLD). Excessive alcohol intake and liver infections such as hepatitis can also cause elevations.

When to check

Baseline. If the baseline result is abnormal, repeat every 3-6 months.

Standard reference ranges
Women: 10-25 IU/L
Men: 10-33 IU/L
Women: 0,25-0,60 µkat/L
Men: 0,25-0,75 µkat/L
Low-carb considerations

Elevated ALT due to metabolic syndrome or NAFLD tends to improve on a low carb diet, at least longer term.1

Occasionally, ALT might increase during the initial three months on starting a low-carb diet, coinciding with weight loss. Once the weight loss is over, this elevation tends to disappear and ALT usually normalizes.2

Elevated levels

Higher than normal values may be caused by:3

  • NAFLD (most commonly), or liver cirrhosis
  • High alcohol consumption
  • Drug side effects, e.g. statins, aspirin, some sleep aids
  • Mononucleosis

Extremely high values may be caused by:

  • Acute viral hepatitis
  • Overdose of drugs like acetaminophen (Tylenol)
  • Liver cancer

 

More

ALT is found in serum and in various body tissues, but is primarily associated with the liver. It is commonly measured as part of a diagnostic liver function test to determine liver health. The transaminases (ALT and AST) are the most sensitive tests of hepatocellular damage but are not very specific. Since many patients with NAFLD have normal ALT levels, an abdominal ultrasound is recommended to diagnose NAFLD.


Fasting glucose

Fasting blood glucose (FBG) is most commonly used to diagnose or assess diabetes, monitor hyperglycemia and hypoglycemia, and aid in diabetes treatment decisions.

When to check

Baseline and annually at a minimum. However, many may find value checking multiple times per day or even continuously with a continuous glucose monitor (CGM). This allows real time feedback as to the effect food and other lifestyle choices have on blood sugar.4

Standard reference ranges
Average diet: 65 – 100 mg/dL
On low carb: 54 – 100 mg/dL (or higher, see below)5
3.8 – 5.5 mmol/L
On low carb: 3.0 – 5.5 mmol/L (or higher, see below)

 

Elevated levels

Higher than normal values may be caused by:

  • Type 1 or type 2 diabetes
  • Acromegaly
  • Acute/chronic pancreatitis
  • Cushing’s syndrome
  • Drug side effects: glucocorticoids
  • Pheochromocytoma
  • Stress

 

Decreased levels

Lower than normal values may be caused by:

  • Adrenal insufficiency
  • Alcohol consumption
  • Exogenous insulin
  • Hypopituitarism
  • Hypothyroidism
  • Insulinoma
  • Malignancy
  • Malnutrition
  • Drug side effects, e.g oral hypoglycemic agents
  • Sepsis

 

Low-carb considerations

Patients eating low carb may have much lower FBG levels than patients following the traditional food pyramid.6 Standard reference ranges reflect a society of carb-burners, not fat-burners. Once a low carb patient transitions into a fat-burner and has circulating ketones, they may have a lower demand for glucose to maintain normal body function.7 FBG levels may consistently lie between 3.0 to 3.9 mmol/L or 54 to 70 mg/dL once the patient has been following low-carb for several months.

However, FBG numbers can also go up on low carb, which can surprise patients and doctors alike. This common occurrence is the “dawn phenomenon” and reflects that muscles are in “glucose refusal mode” — or what some low carb doctors have dubbed “adaptive glucose sparing.” Generally, this is not a concern as the rest of the day blood glucose will remain low.8 The FBG may be the highest value of the day.

 

 

Hemoglobin A1c (HbA1c)

Hemoglobin A1c (HBA1c) estimates the average glucose level in the blood over the previous three months by counting the number of glucose molecules stuck on red blood cells. Glucose molecules on hemoglobin is called glycated, or glycosated hemoglobin.

When to check

Baseline. If abnormal, repeat every 3 months.

Standard reference ranges

Normal values: 4.0 to 5.6%

Pre-diabetes: 5.7 to 6.4%

Diabetes: ≥ 6.5% 

 

Elevated values

Higher than normal values may be caused by:

  • Diabetes (type 1 and 2)
  • Pre-diabetes
  • Low red blood cell (RBC) turn over, e.g. anemia of iron deficiency
  • B12 deficiency, folate deficiency

 

Decreased values

Lower than normal values may be caused by:

  • High RBC turn over, e.g.hemolytic anemia
  • Use or abuse of erythropoietin (EPO)
  • Treatment for iron deficiency, B12 deficiency, or folate deficiency
  • Patients on hemodialysis (which alters the RBC turn over)

 

Low-carb considerations

Ordering HbA1c tests every three months can motivate and empower patients to continue the low carb diet.9 If values are dropping they get positive reinforcement; if values rise, they may be motivated to adhere more strictly to the low-carb diet. Rising values in formerly successful patients who may be slipping back into old dietary habits can convince them to get back on track.

Some patients have HbA1c levels that stall or even rise at the start of low-carb, especially as they reduce their diabetic medications. Let them know this is okay.

Example: a patient has a baseline HbA1c of 7.4%, but daily was taking 100 units of long acting insulin, a high dosage of a sulfonylurea, and an SGLT2-inhibitor. After going low-carb, the patient was able to discontinue all her diabetic medications within six months. Her six month HbA1c level is still 7.4%. The patient feels frustrated and confused that her HbA1c did not go down despite all her hard work.

This is a common situation in low-carb clinics.10 But you can help the patient see how this is an improvement! A lot of insulin plus three additional diabetic medications used to control their diabetes; now they don’t need any medications to have an HbA1c of the same level. This likely demonstrates increased insulin sensitivity and should improve over time. Checking it regularly will help reinforce that.

More

HbA1c results may not be accurate for patients with chronic kidney disease (CKD), underestimating true blood glucose values. Results may also be inaccurate with some genetic hemoglobin variants, such as persistence of fetal hemoglobin (HbF) or existence of sickle cell anemia, either measuring too high or too low against real blood glucose values.11

 

Complete lipid panel

The complete lipid panel measures total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglycerides. It is primarily used to assess cardiac risk and make decisions regarding treatment for patients who appear to be at high-risk.

When to check

Baseline. Repeat every 6 months. If a patient appears to be a hyper-responder — having LDL-C levels significantly higher on low carb — consider repeating every 3 months until stable, then repeat every 6 months.

Standard reference ranges
Total cholesterol
<200 mg/dL
<5.2 mmol/L
HDL-C
>40 mg/dL for men and >50mg/dl for women
>1.0 mmol/LL
LDL-C
<100 mg/dL (however, it is difficult to assign an exact number that is elevated as LDL levels should be taken as part of the overall CV risk and therefore numbers of concern may vary between individuals)
<2.6 mmol/L
Triglycerides
<150 mg/dL
<1.8 mmol/L
Low-carb considerations

Patients should fast for 12 hours prior to a lab test for a complete lipid panel as eating can cause large fluctuations in triglyceride levels. Keep in mind the “normal” values were likely determined on people eating high carb diets. Most patients eating low carb will have much lower triglyceride levels. Therefore, low carb doctors consider the optimal triglyceride levels for patients on low-carb to be less than 100mg/dL and close to 70 mg/dL (<0.8 mmol/L).

Most studies show that patients eating low carb do not see a significant increase in LDL, and instead see a decrease in TG and increase in HDL.12 However, some may see an initial increase in LDL during active weight loss that tends to normalize over the first six to twelve months. It may be important to keep this association with weight loss in mind when trying to determine if action is required.13

For an estimated 5 to 25% of people – whether weight loss occurs or not – LDL cholesterol can go up significantly in response to very-low-carb diets, sometimes by 200% or more.14 Many of these folks seem to belong to a group that Dave Feldman at Cholesterol Code refers to as lean mass hyper-responders (LMHRs).15 These often healthy people are sometimes shocked to discover that their LDL cholesterol has soared above 200 mg/dL (5.2 mmol/L) after going keto. Unfortunately, we lack scientific data on this specific subset of individuals, and therefore the approach should be individualized in each case. You can read more about in our related guides on low-carb and cholesterol, what our stance is on LDL cholesterol, and how one can lower LDL while on a low-carb diet.


Creatinine

The creatinine test is a clinical marker for kidney function. Serum levels of creatinine, a waste product from the normal wear and tear of muscles, will vary depending on patients’ muscle mass, age, sex, and their glomerular filtration rate (GFR). Therefore, normal reference ranges may also vary depending on these variables.

When to check

Baseline. Repeat every 6 months if abnormal or the patient is known to have CKD.

Standard reference ranges
0.8-1.4 mg/dL (keep in mind the normal range is variable based on gender, age, and amount of muscle mass)
61-107 µmol/L
Increased values

Higher than normal values may be caused by:

  • Acute tubular necrosis
  • Drug side effects, e.g. aminoglycoside antibiotics
  • Congestive heart failure
  • Dehydration
  • Diabetic nephropathy
  • Glomerulonephritis
  • Renal failure
  • Hypothyroidism
  • Muscular dystrophy
  • Pyelonephritis
  • Rhabdomyolysis
  • Shock
  • Urinary track obstruction

 

Decreased values

Lower than normal values may be caused by:

  • Decreased muscle mass
  • Myasthenia gravis
  • Muscular dystrophy

 

Low-carb considerations

Low-carb patients lose excess water weight in the first weeks to months of adopting their new diet.16 Low-carb doctors may observe an initial mild increase in creatinine levels as a result.17 These levels return to normal within 2-3 months of maintaining a low-carb diet.

Some may have concern that low-carb or keto diets are potentially harmful for kidney function. This however, is a myth not supported by scientific evidence. We cover this thoroughly in our guide to low-carb and kidney function.

 

Microalbumin/creatinine ratio, urine

Microalbumin/creatinine ratio (urine) is commonly used as a marker to detect early diabetic nephropathy. Also known as microalbumin, ACR, UACR, urine albumin, the test measures when kidneys leak small amounts of albumin into the urine. Microalbuminuria is diagnosed either from a 24-h urine collection or from elevated concentration in a spot urine sample. Both must be measured on at least two of three measurements over a two to three-month period.18

When to check

Baseline. If abnormal or the patient has CKD, repeat every 6 months. Once levels are stable, repeat annually.

Standard reference ranges
less than 30mg/dL represent normal values, and values between 30-300 mg/L may indicate early kidney disease
30 to 300 mg/L

 

Increased values

Higher than normal values may be caused by:

  • Chronic kidney disease (CKD)
  • Cardiovascular disease
  • Type 1 or type 2 diabetes
  • Diabetic nephropathy
  • Hypertension
  • Vascular endothelial dysfunction

 

Low-carb reference considerations

There is not much data on improvement of albumin to creatinine ration on low-carb diets, but anecdotal experience and a published case report does suggest this may occur.19 However, it is unlikely that low-carb diets worsen renal function as we cover in our guide on low-carb diets and kidney function.

 


Optional blood tests

Depending on other medical conditions your patients may have — such as chronic kidney disease or hypothyroidism — you may want to order other tests. Patients may also struggle with the induction or keto flu when transitioning to a low-carb diet. Certain tests, such as sodium and vitamin B12, may help rule out any other factors that may be causing their symptoms.


Complete blood count (CBC)

CBC (complete blood count) measures the red, white and platelet blood cells in the blood. Red blood cells (erythrocytes) deliver oxygen while white blood cells (leucocytes) are part of the immune system, and platelets (thrombocytes) help in the clotting process. Red blood cells live approximately 120 days, or 3 months, which is why the HbA1c is measured at least 3 months apart.20

When to check

If your patient is struggling with fatigue, appears pale, or has any bleeding issues.

Standard reference ranges
WBCs (white blood cells)
4,500-10,000 cells/mcL
RBC (red blood cell count)
Women: 4 million-5 million cells/mcL
Men: 5 million-6 million cells/mcL
Women: X
Men:X
Hb or Hbg (hemoglobin)
Women: 12 to 15 gm/dL
Men: 14-17 gm/dL
Women: X
Men:X
Hct (hematocrit)
Women: between 36% and 44%
Men: between 41% and 50%
Women: X
Men:X
MCV (mean corpuscular volume)
MCV score is 80 to 95
Platelets
140,000-450,000 cells/mcL
Increased values

Higher than normal values may be caused by:

  • Congenital heart disease
  • Dehydration
  • High altitude
  • Hypoxia (such as from undiagnosed sleep apnea)
  • Malignancy
  • Polycythemia vera
  • Pulmonary fibrosis
  • Thalassemia

 

Decreased values

Lower than normal values may be caused by:

  • Anemia
  • Chronic renal failure
  • Alcohol dependence
  • Drug side effect, e.g. allopurinol
  • Liver disease

 

Low-carb considerations

Checking CBC may be helpful if your patient is experiencing unexplained fatigue or mental fog. These symptoms can also occur if the patient has a sub-optimal intake of protein, calories or salt, or has the induction or keto-flu.21

 

Electrolytes (sodium and potassium)

Sodium

Testing for sodium levels can help troubleshoot concerning symptoms, such as fatigue, muscle cramps and headache on a low carb diet. Sodium is an essential electrolyte that helps with blood volume regulation, blood pressure, fluid balance, nerve induction, muscle contraction, maintenance of osmotic equilibrium, and acid-base balance.

When to check

Baseline. Repeat every 6 months for patients with CKD

Standard reference ranges
134-144 mEq/L
134-144 mmol/L

 

Increased values

Higher than normal values may be caused by:

  • Cushing’s syndrome/disease
  • Dehydration
  • Too high dietary sodium intake
  • Type 1 or type 2 diabetes
  • Diabetes insipidus
  • Excessive diaphoresis
  • Advanced age
  • Hyperaldosteronism
  • Oral contraceptive pills
  • Vomiting

 

Decreased values

Lower than normal values may be caused by:

  • Drug side effects: e.g. ACE inhibitors, thiazide diuretics
  • Acute tubular necrosis
  • Adrenal insufficiency
  • Congestive heart failure
  • Cirrhosis
  • Diarrhea
  • Excessive exercise
  • Heavy sweating
  • Hypothyroidism
  • Malnutrition
  • Nephrotic syndrome
  • Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
  • Vomiting
  • Water intoxication
  • Too low dietary sodium intake

 

Low-carb considerations

Sometimes healthy patients and even renal patients, despite their CKD, must supplement with salt when adopting a low-carb diet.22 Patients who are no longer consuming excess sodium in processed food items will lose water weight, and may be less prone to water retention.23 Low-carb doctors often find that their CKD patients’ sodium levels may stay within the lower end of the normal reference range, but decrease enough to correlate with the patient experiencing minor symptoms of hyponatremia, such as headache, confusion, muscle cramps, weakness, and fatigue.

 

Potassium

Testing potassium (K+) levels can help trouble shoot muscle cramps, fatigue and other symptoms. Potassium is an essential electrolyte that is involved in a wide array of body functions, particularly muscle contraction, nerve conduction, heart rhythm, and acid-base balance.

When to check

Baseline. Repeat every 6 months for patients with CKD

Standard reference ranges

US units: 3.6-5.0 mEq/L
SI units: 3.6-5.0 mmol/L

 

Increased values

Higher than normal values may be caused by:

  • Drug side effects: e.g ACE inhibitors, angiotensen receptor blockers (ARBs), beta blockers, spironolactone and NSAIDs
  • Acidosis
  • Acute/chronic renal failure
  • Addison’s disease
  • Dehydration
  • Type 1 and 2 diabetes
  • Infection
  • Massive tissue damage
  • Massive hemolysis
  • Renal tubular acidosis

 

Decreased values

Lower than normal values may be caused by:

  • Ascites
  • Burns
  • Chronic pyelonephritis
  • Cushing’s syndrome
  • Drug side effects, e.g. diuretics, salicylates, prolong corticosteriods, exogenous insulin
  • Diarrhea
  • Eating disorders, especially bulimia and/or laxative abuse
  • Hyperaldosteronism
  • Hypothyroidism
  • Low potassium intake
  • Metabolic alkalosis
  • Renal tubular acidosis
  • Vomiting

 

Low-carb considerations

Potassium supplementation is generally not needed for most low-carb patients. If, instead, your patient has hyperkalemia, see if adjustments to medications, such as for blood pressure, can be made. If they cannot, you will need to advise patients to avoid high potassium foods such as avocados, mushrooms and spinach.


Fasting insulin or c-peptide

Testing fasting insulin, or c-peptide, can provide insight into a patient’s degree of insulin production, insulin sensitivity or insulin resistance.24 For fasting measurements, c-peptide may have less variability that insulin, but both tests give similar information so doing both is likely not necessary.

Both tests assess the body’s creation and use of insulin, a hormone secreted by the isles of Langerhans in the pancreas. Central to regulating carbohydrates and fat metabolism in the body, insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood. Insulin resistance is the underlying cause of type 2 diabetes.

A fasting insulin level along with a fasting glucose can be used to calculate a HOMA-IR, which provides a fairly accurate assessment of metabolic syndrome, and likely better than simply fasting blood glucose or HbA1c alone.25

Traditionally, a c-peptide test is measured as a means of distinguishing between type 1 and type 2 diabetes.26 However, as described here, it may also help in detecting insulin resistance well before the onset of type 2 diabetes.27

When to check

Baseline and every 6 months

Standard reference ranges
Fasting insulin levels: 2-12 mU/mL. It is important to note that this test is relatively new for monitoring metabolic health, and the exact reference range is not well defined.
Fasting c-peptide levels: 0.78-1.89 mg/mL
Fasting insulin levels: 12-72 pmol/L
Fasting c-peptide levels:0.26-0.62 nmol/L

 

Increased fasting insulin

Higher than normal values may be caused by:

  • Acromegaly
  • Cushing’s syndrome
  • Type 2 diabetes
  • Drug side effects, e.g. glucocorticoids, hypoglycemic agents, insulin (exogenous)
  • Liver disease
  • Insulinoma
  • Obesity
  • Uremia

 

Decreased fasting insulin

Lower than normal values may be caused by:

  • chronic pancreatitis
  • Type 1 diabetes
  • Hypopituitarism.

 

Increased c-peptide values

Higher than normal values may be caused by:

  • Type 2 diabetes
  • Insulinoma
  • Renal failure

 

Decreased c-peptide values

Lower than normal values may be caused by:

  • Type 1 diabetes
  • Radical pancreatectomy
  • Latent adult onset diabetes (LADA)

 

Low-carb reference considerations

Insulin and c-peptide levels are very sensitive to stress, infection, lack of sleep or a recent high carb meal. Significant short term variations can be very frustrating for patients. Checking these levels regularly can help display trends which may be more helpful in assessing progress (or lack of progress) with dietary interventions.

Once a low carb patient is fat-adapted, fasting insulin or c-peptide tend to decrease.

Low-carb reference ranges for fasting insulin

US units: 0.3 – 5.8 mU/mL
SI units: 2 – 40 pmol/L

Many low carb experts try to target levels between 0.3 – 2.9 mU/mL28

Low-carb reference ranges for fasting c-peptide

US units: 0.39 – 1.98 mg/mL
SI units:0.13 – 0.62 nmol/L

These are normal ranges for low carb patients, however, if they are consuming carbohydrates these levels could indicate the onset of type 1 diabetes or late onset type 1 diabetes (LADA). LADA should be considered in low-carb patients whose insulin or c-peptide remains low but their blood glucose continues to rise.

High-sensitivity c-reactive protein (hs-CRP)

The high-sensitivity c-reactive protein test (hs-CRP) is used as a marker for inflammation. Measuring and charting CRP values can help determine disease progress or the effectiveness of treatments. It can be a warning sign that the body is reacting to something in the diet (e.g. gluten or refined carbs) or body (e.g. infection or chronic inflammation).

CRP is synthesized by the liver as part of the body’s immune complement system, binding to dead or dying cells to help mark them for clearance by phagocytes.

When to check

Baseline. Repeat every 3-6 months for patients who have an inflammatory condition or who are doing significant dietary experiments.

Standard reference ranges

<3 mg/L

 

Increased values

Higher than normal values may be caused by:

  • Atherosclerosis
  • Rheumatoid arthritis
  • Autoimmune disease
  • Infections
  • Inflammatory disease
  • Malignancy

 

Low-carb considerations

CRP levels often reduce in patients on low carb diets, providing tangible evidence that inflammation is decreasing and reinforcing commitment to the lifestyle.29 Frequently, symptoms of inflammation, such as joint pain or swelling, may also improve.30


Nuclear magnetic resonance (NMR) lipoprofile

A nuclear magnetic resonance (NMR) lipoprofile, or particle test, is a more detailed test of circulating cholesterol that can help refine a patient’s risk of developing cardiovascular disease. This test can be particularly helpful in measuring low-density lipoproteins (LDL) particles, and evaluating them according to their number and particle size.

When to check

Baseline and annually, or sooner if significant dietary changes are being made.

Low-carb considerations

This test is not available everywhere and may not be covered by insurance. Low-carb diets tend to be effective at reducing the amount of small LDL and increasing the overall LDL size. For those who see a rise in their LDL, the so-called hyper-responders, this test may be helpful to ensure there is a rise in the larger, less dense particles and not in the smaller, more concerning particles.

 

Thyroid stimulating hormone (TSH)

A thyroid-stimulating hormone test checks whether a patient’s thyroid may be underactive or overactive. The test measures blood levels of TSH, secreted by the pituitary to tell the thyroid how much T3 and T4 to produce. An abnormal TSH value does not always indicate hypo or hyperthyroidism. The interpretation of TSH also depends on blood levels of T3 and T4, as well as the clinical symptoms of thyroid conditions and a physical exam.

When to check

Baseline if the patient has a history of hypothyroidism and Hashimoto’s disease, or takes thyroid medication. Repeat every 3 months until levels stabilize, then repeat annually.

Standard reference ranges
0.35-5.5 µU/mL
0.35-5.5 mU/L

 

Increased values

Higher than normal values may be caused by:

  • Hypothyroidism
  • Hashimoto’s disease
  • The recovery phase of acute illness

 

Decreased values

Lower than normal values may be caused by:

  • Acute medical or surgical illness
  • Grave’s disease
  • Hyperthyroidism
  • Drug treatments, e.g. glucocorticoids or somatostatin analogs

 

Low-carb considerations

Patients with pre-existing hypothyroidism or Hashimoto’s disease may experience mild or even significant improvement of their thyroid function on a low carb diet.31 Some low-carb doctors have even been able to discontinue the thyroid medication of their hypothyroid patient. Other patients may need their thyroid medication reduced if they experience symptoms of hyperthyroidism, which may come in waves over a few months on a low carb diet. The low-carb diet does not need to be stopped during periods where the patient experiences symptoms of hyperthyroidism, some recommend avoiding fasting until the patient is stable on the adjusted dosage of medication.32

A frequent symptom of hypothyroidism is fatigue. This can be confused with a sub-optimal intake of calories, protein, or the induction or keto-flu. Checking TSH levels can help determine why your patient may be experiencing these symptoms.


Uric acid

The uric acid test helps assess the patient on the metabolic syndrome spectrum. A product of purine breakdown, found in urine, uric acid levels are an independent risk factor for diabetes. Excess uric acid can cause gout and kidney stones. Levels can be affected by diet, alcohol consumption, and kidney function.

When to check

Baseline. Repeat every 6 months in patients with a history of gout.

Standard reference ranges
4.0 to 8.0 mg/dL (although the normal range may be slightly lower for females than for males)
240 – 480 umol/L

 

Low-carb considerations

Uric acid can temporarily increase when patients start low-carb. This may be observed within the first six weeks as patients transition into a fat-burning state, with eventual normalization.33

Patients with a history of gout may be at increased risk of triggering another one in the first six weeks of going low carb, but studies to date do not confirm this. The pros and cons of prophylaxis treatment should be discussed with patients at risk for gout.

 

Vitamin B12

Vitamin B12 (cobalamin) levels may help distinguish reasons for fatigue or other symptoms that may be related to diet, malabsorption, or malnutrition. Vitamin B12 is a water-soluble vitamin that plays a key role in the functioning of the brain and nervous system and the formation of red blood cells. It is involved in the metabolism of every cell of the human body, especially DNA synthesis and regulation, fatty acid synthesis, and energy production.34

When to check

Baseline for vegetarian and vegan patients, and patients with a history of gastric bypass or lap-band surgery. If abnormal, repeat every 6 months.

Standard reference ranges
180-900 ng/L (note that reference ranges vary among different labs. The quoted reference here is based on the Mayo Clinic standard lab)
150-500 pmol/L

 

Decreased values

Lower than normal values may be caused by:

  • Bowel resection (gastric bypass surgery, gastrectomy)
  • Celiac disease
  • Crohn’s disease
  • Dietary deficiency (veganism)
  • Helminth infection
  • Hyperthyroidism
  • Malabsorption
  • Drug side effects, e.g, metformin, oral contraceptive pill
  • Pernicious anemia
  • Pregnancy

 

Low-carb reference considerations

A low carb diet rich in animal products should provide adequate B12 levels. Of note, if a patient has macrocytic anemia related to a B12 deficiency, this can lead to an inaccurate (higher) HbA1c test result. One of the most frequent symptoms of vitamin B12 deficiency is fatigue and mental fog, which can be confused with a sub-optimal intake of protein, calories, or the induction or keto-flu. Checking vitamin B12 levels can help determine why your patient may be experiencing these symptoms.


More

Back to main low carb for doctors guide

  1. Hepatology Research 2018: Comparison of efficacy of low-carbohydrate and low-fat diet education programs in non-alcoholic fatty liver disease: A randomized controlled study [randomized trial; moderate evidence]

    Journal of Medicinal Food 2011: The effect of the Spanish Ketogenic Mediterranean diet on nonalcoholic fatty liver disease: A pilot study [non-controlled study; weak evidence]

  2. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  3. Postgraduate Medical Journal 2016: Evaluation of abnormal liver function tests [overview article; ungraded]

  4. This is based on clinical experience of low-carb practitioners and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence].

  5. Clinical experience suggests that when ketones are present, people can tolerate lower blood sugar levels

  6. This is based on clinical experience of low-carb practitioners and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence].

  7. This is based on clinical experience of low-carb practitioners and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence].

  8. This is based on clinical experience of low-carb practitioners and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence].

  9. This is based on clinical experience of low-carb practitioners and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence].

  10. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  11. Journal of General Internal Medicine 2014: Pitfalls in hemoglobin A1c measurement: when results may be misleading [overview article; ungraded]

  12. Cardiovascular Diabetology 2018: Cardiovascular disease risk factor responses to a type 2 diabetes care model including nutritional ketosis induced by sustained carbohydrate restriction at 1 year: an open label, non-randomized, controlled study. [non-randomized trial; weak evidence]

    Nutrition in Clinical Practice 2011: Low-carbohydrate diet review: shifting the paradigm [review article; ungraded]

    Nutrition Reviews 2019: Effects of carbohydrate-restricted diets on low-density lipoprotein cholesterol levels in overweight and obese adults: a systematic review and meta-analysis [systematic review of randomized trials; strong evidence]

    British Journal of Nutrition 2016: Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials [strong evidence]

  13. The American Journal of Clinical Nutrition 1991: The transient hypercholesterolemia of major weight loss. [non-randomized trial; weak evidence]

    Journal of the American College of Nutrition 1983: Effect of weight reduction on circulating lipids: An integration of possible mechanisms [observational study, weak evidence]

    Journal of Nutrition 1960: Serum cholesterol in acute starvation: A report of 20 cases [nonrandomized study, weak evidence]

  14. This is based on clinical experience of low-carb practitioners and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence].

  15. Although Dave is not a physician or scientist, he is an engineer with a knack for self-experimentation. Through his self-experimentation, he has shown how he can dramatically change his LDL cholesterol level over the course of days to weeks just by altering his diet.

  16. It’s been known for decades that when insulin levels drop —as they do when carb intake is very low—the kidneys excrete more sodium and water, although the exact mechanism isn’t clear:

    American Journal of Physiology. Renal Physiology 2007: Insulin’s impact on renal sodium transport and blood pressure in health, obesity, and diabetes [overview article; ungraded]

    Diabetalogia 1981: The effect of insulin on renal sodium metabolism [overview article; ungraded]

  17. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  18. Journal of Natural Science and Biological Medicine 2015: Assessment of microalbuminuria and albumin creatinine ratio in patients with type 2 diabetes mellitus [overview article; ungraded]

  19. Nutrition & Metabolism 2006: A low-carbohydrate diet may prevent end-stage renal failure in type 2 diabetes: a case report [case study; very weak evidence]

  20. However, as we mention in our guide on HgbA1c, there are many factors which may alter the lifespan of red blood cells

  21. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  22. This is based on clinical experience of low-carb practitioners and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence].

  23. American Journal of Physiology. Renal Physiology 2007: Insulin’s impact on renal sodium transport and blood pressure in health, obesity, and diabetes [overview article; ungraded]

    Diabetalogia 1981: The effect of insulin on renal sodium metabolism [overview article; ungraded]

  24. Diabetes Therapy 2017:
    A practical review of C-peptide testing in diabetes
    [overview article; ungraded]

  25. Diabetes Care 1996: A prospective analysis of the HOMA model. The Mexico City Diabetes Study [observational study, weak evidence]

    Diabetes care 2000: Homeostasis model assessment closely mirrors the glucose clamp technique in the assessment of insulin sensitivity: studies in subjects with various degrees of glucose tolerance and insulin sensitivity [nonrandomized study, weak evidence]

  26. C-peptide is a remnant from the multi-step creation of insulin by the pancreas. Its levels can indicate the amount of insulin the pancreas is making, or whether it is still producing any insulin at all. C-peptide levels in type 2 diabetes are normal or elevated. C-peptide in type 1 diabetes is low or non-existent.

  27. This is based on clinical experience of low-carb practitioners and was unanimously agreed upon by our low-carb expert panel. You can learn more about our panel here [weak evidence].

  28. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  29. Metabolism 2013: Consuming a hypocaloric high fat low carbohydrate diet for 12 weeks lowers C-reactive protein, and raises serum adiponectin and high density lipoprotein-cholesterol in obese subjects [randomized trial; moderate evidence]

  30. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  31. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  32. This is based on anecdotal clinical experience

  33. Nutrition 2012: Effect of low-calorie versus low-carbohydrate ketogenic diet in type 2 diabetes. [randomized trial; moderate evidence]

    NEJM 2003: A Low-Carbohydrate as Compared with a Low-Fat Diet in Severe Obesity [randomized trial; moderate evidence]

  34. Nutrients 2010: Vitamin B12 in health and disease [overview article; ungraded]