Nutrition check for a vegan diet

For follow-up

Nutrition blood test for a vegan or vegetarian diet with vitamin B12, homocysteine, ferritin, full iron studies, vitamin D, folic acid, zinc, selenium, magnesium, proteins, TSH and general biochemistry. It shows whether supplementation and diet are keeping the most relevant parameters within an appropriate context.

No prescription or appointment needed

Results in 3-5 working days

Blood and urine sample. Includes: Full blood count · Glucose · Urea, creatinine and eGFR · Uric acid · Sodium and potassium · Lipid profile and ratios. 19 in total. See what each one measures

What it is for

It is a nutrition check for a vegan or vegetarian diet kept up over time. The priority is to check vitamin B12 and iron, and to add context with vitamin D, zinc, selenium, proteins and general parameters.

A well-planned vegan diet can be adequate, but vitamin B12 requires a reliable supplemental source. The blood test shows the situation with your usual regimen, although no result replaces reviewing the amount and regularity of supplementation.

When it is recommended

Periodic monitoring of a strict vegan or vegetarian diet
The first year after cutting out animal foods
Doubts about the regularity or dose of vitamin B12 supplementation
Tiredness, tingling, hair loss or other new symptoms on a plant-based diet
Heavy periods, a planned pregnancy or a history of low iron together with a vegetarian or vegan diet

Clinical comment

Total vitamin B12 can fall in an indeterminate range. Homocysteine adds functional context, but it also rises with folate deficiency, kidney disease and other causes. If doubt remains, methylmalonic acid is a more specific second-line test.

Iron is assessed with ferritin and iron studies because a normal ferritin can be misleading if there is inflammation. This is especially relevant with heavy periods, pregnancy, frequent blood donation or low intake.

TSH is included to assess thyroid function, not as a measure of iodine. A normal TSH does not guarantee that iodine intake is adequate, and a thyroid abnormality has many causes. Using iodised salt and reviewing the diet remain the practical way to check that point.

Dr. Antonio Mas

What is tested

Full blood count: Looks for anaemia and other changes in the blood cells.
Glucose: Measures fasting blood sugar.
Urea, creatinine and eGFR: Assess kidney function and add context about hydration and protein metabolism.
Uric acid: Completes the metabolic and kidney assessment.
Sodium and potassium: Measure the main electrolytes in the blood.
Lipid profile (total cholesterol, HDL, LDL, triglycerides) and ratios
AST, ALT, GGT and total bilirubin: Give information about the liver.
Ferritin: Estimates iron stores, although it can also rise with inflammation.
Iron studies (iron, transferrin, saturation and total iron-binding capacity)
Vitamin D (25-OH): Assesses vitamin D stores.
Vitamin B12: Checks the circulating level of a vitamin that requires reliable supplementation on a vegan diet.
Folic acid (folate): Assesses folate, which is usually plentiful in a varied plant-based diet but relevant for interpreting the full blood count and homocysteine.
Magnesium: Measures serum magnesium, which represents a small part of the body's stores.
Zinc: Assesses a mineral whose absorption can be affected by the phytates in some plant foods.
Selenium: Measures a trace element whose intake depends on the soil and on food choices.
Homocysteine: Can rise with a functionally insufficient supply of B12 or folate, although it is not specific.
Total protein and albumin: Add context about synthesis and losses, but do not directly measure diet quality or muscle mass.
Urinalysis and sediment: Looks for protein, blood, glucose, white blood cells and other urinary abnormalities.
TSH: The first test of thyroid function, but it does not directly measure iodine intake.

How to prepare

Fast for 8 to 12 hours. You can drink water. Bring a sample of your first urine of the morning or collect it at the partner centre. If you take biotin supplements, stop them 48 hours before, because they can interfere with several tests.

Keep taking your usual vitamin B12 supplement so that the result reflects your real regimen. Oral iron can temporarily change serum iron; check whether you should have the sample taken before your dose. Do not stop a prescribed treatment on your own.

Related blood tests

We have other profiles in Nutrition with more or fewer tests:

The most comprehensive is not always the most useful. If you are not sure, the one we recommend to start with is Basic nutrition blood test.

What it is based on

Academy of Nutrition and Dietetics · J Acad Nutr Diet 116(12):1970-1980
Position of the Academy of Nutrition and Dietetics: Vegetarian Diets
It supports the two ideas behind this protocol. The first is that a well-planned vegan diet is adequate at all stages of life, so monitoring it means watching a few points and not all of them. The second is the reason for measuring homocysteine: the paper states that subclinical B12 deficiency shows up as raised homocysteine. It adds iodine to what can fall short without iodised salt, which is why TSH is checked here, and describes low ferritin as the usual iron finding in plant-based diets. One nuance: among the tests of B12 status it also names methylmalonic acid and holotranscobalamin, and neither of them is in this profile.
National Institute for Health and Care Excellence
Vitamin B12 deficiency in over 16s: diagnosis and management (NG239)
It places diets that exclude animal products among the risk factors that justify investigating B12, and sets the order of tests: total B12 or active B12 first, and methylmalonic acid if the result is indeterminate. Homocysteine remains an alternative, with the caveat that it also rises with folic acid deficiency, which this profile measures.

Protocol designed by Dr. Antonio Mas, specialist in Endocrinology and Nutrition, Spanish medical licence no. 080846289, and reviewed in September 2026.

This blood test is a standardised protocol and does not replace a medical consultation. If you have symptoms, a known condition or a complex clinical situation, speak to your doctor.