Vitamin B complex blood tests, one vitamin at a time

"B vitamins" sounds like one thing, but it is a family of eight different nutrients with different jobs. B12 and folate get most of the attention, and we cover them in a separate guide. This one goes through the others, the ones people see on supplement labels but rarely see on a test request: B1, B2, B3, B5, B6 and B7.

A vitamin B complex blood test is not something most people need routinely. It tends to be used with guidance from a professional, when there is a specific reason to look. Knowing what each vitamin does helps make sense of that conversation.

What the B vitamins have in common

The B vitamins are water-soluble and act as helpers (coenzymes) in many of the chemical reactions that turn food into energy and keep cells working (Hanna et al., 2022). The NHS notes that several of them, such as thiamin and riboflavin, cannot be stored in the body, so they are needed in the diet every day. It also says most people can get all the B vitamins they need from a varied and balanced diet.

The B vitamins one by one

Vitamin B1 (thiamine)

According to the NHS, thiamin helps the body break down and release energy from food and keeps the nervous system healthy. Good sources include peas, some fresh fruit, nuts, wholegrain bread and some fortified cereals. Reviews describe thiamine deficiency as more likely in people with heavy alcohol use, after some types of weight-loss surgery and in severe malnutrition (Smith et al., 2021). LML describes its VITAMIN B1 (Thiamine) test as a way to help identify a shortage.

Vitamin B2 (riboflavin)

Riboflavin helps keep the skin, eyes and nervous system healthy and helps release energy from food. Milk, eggs, fortified cereals, mushrooms and plain yoghurt are good sources. The NHS adds a practical detail: UV light can destroy riboflavin, so these foods are best kept out of direct sunlight. LML's Vitamin B2 (Riboflavin) test describes it as important for energy production, cell function and metabolism.

Vitamin B3 (niacin)

Niacin helps release energy from food and keeps the nervous system and skin healthy. It comes in two forms, nicotinic acid and nicotinamide, and is found in meat, fish, wheat flour and eggs. The VITAMIN B3 (NICOTINAMIDE) test in the catalogue measures the nicotinamide form.

Vitamin B5 (pantothenic acid)

LML describes vitamin B5 as a nutrient involved in energy production, hormone production and skin health. The NHS notes that pantothenic acid is found in varying amounts in almost all vegetables, wholegrain foods and meats, which is part of why it is less often discussed. The Vitamin B5 (Pantothenic Acid) test is a specialised one, and LML lists a turnaround of about 2 weeks.

Vitamin B6 (pyridoxine)

The Vitamin B6 (Pyridoxine) test measures pyridoxal 5-phosphate (PLP) and its precursor. LML explains that B6 is needed for many metabolic reactions, including the formation of serotonin, and that a shortage can come from diet, from some medicines (it names isoniazid and penicillamine) or, rarely, from an inherited condition.

Vitamin B7 (biotin)

Biotin plays a part in several metabolic processes. LML lists situations in which the Vitamin B7 (Biotin) test is used: a rare inherited condition called biotinidase deficiency, poor intake or absorption, pregnancy, when needs increase, and some medicines such as certain anticonvulsants.

The Vitamin B Profile

Instead of choosing vitamins one by one, the VITAMIN B Profile groups six markers in one request: vitamins B1, B2, B3 and B6, plus red cell folate and vitamin B12. LML reports it about 5 days after the sample arrives. It can be a practical option when a professional wants a broad look at B vitamin status, for example in someone with a very restricted diet or a condition that affects absorption.

Why these samples need extra care

Some B vitamins are sensitive to light. LML asks for the B1, B2 and B6 samples to be protected from light, wrapped in foil. The Vitamin B Profile uses several tubes. In practice, this means an LML collection point or a phlebotomist visiting your home is usually the more practical route than a home kit. The individual tests for B1, B2 and B6 are reported in about 2 days, biotin in about 3 days and B3 in about a week.

When does testing make sense?

These are not routine screening tests. The topic's frequency is "with guidance": a professional is the right person to decide whether a test answers a real question. Situations in which it is sometimes discussed include:

• a very restricted or unusual diet over a long period;
• conditions or surgery that affect absorption from the gut;
• regular heavy alcohol use;
• long-term use of medicines known to affect a particular B vitamin;
• checking the effect of supplements a professional has suggested.

Talk to a professional before ordering, especially if you already take a B complex supplement, as it will influence the results.

How the sample is collected

BPR does not collect samples. LML arranges every collection, by home kit, at an LML collection point (search by postcode) or with a phlebotomist at home, and for these light-sensitive tests the last two options are usually the better fit. Under-18s at a collection point must be accompanied by an adult.

All the tests above are in the BPR catalogue. For help choosing, write to [email protected], use the form on our website or message us in the app.

Frequently asked questions

Why is B12 not covered here? B12 and folate have their own guide because they are tested more often and have specific guidance in the UK. The Vitamin B Profile does include both.

If I take a B complex supplement, is testing still useful? It can be, for example to check the effect of a supplement, but the result will reflect what you take. Tell the professional interpreting it about every supplement.

Can I use a home kit for these tests? Because several of these samples must be protected from light or need more than one tube, a collection point or home phlebotomist is usually more practical. The final choice depends on the test.

References

1. Vitamins and minerals - B vitamins and folic acid - NHS. nhs.uk
2. Hanna M, et al. Perm J. 2022;26(2):89-97. PMID 35933667
3. Smith TJ, et al. Ann N Y Acad Sci. 2021;1498(1):9-28. PMID 33305487