Vitamin B2 (riboflavin)

The number depends entirely on the method: whole blood riboflavin ranges of the order of 170 to 470 nmol/L are printed by some UK labs, plasma values are far lower, and the older enzyme activation test (EGRAC) is a ratio where up to about 1.3 is typical, so only the printed range applies.

Riboflavin, vitamin B2, is a water-soluble vitamin from milk, eggs, meat and fortified cereals that the body uses to release energy from food and to handle other B vitamins. Shortage shows as cracked lips and mouth corners, a sore tongue and, over time, anaemia. It is measured either directly in blood or through the activity of an enzyme that depends on it.

It is a specialist test requested in people on very restricted or dairy-free diets, with eating disorders or poor absorption, in some inherited metabolic conditions, and occasionally in unexplained anaemia or mouth and skin changes. It is on a few private nutrition panels.

• Supplements and multivitamins, which raise it within hours and turn the urine bright yellow
• Fortified foods and dairy-rich diets
• Some medicines given as riboflavin for migraine

• Diets low in dairy, eggs and meat, including some vegan diets without fortified foods
• Eating disorders and very restricted diets
• Poor absorption, heavy alcohol use and long-term illness
• Some medicines, including certain antipsychotics and tricyclic antidepressants
• An underactive thyroid, slightly
• Pregnancy and heavy exercise, which increase the need

• A recent supplement raises it
• Light destroys riboflavin, so a sample left in daylight reads low
• Three different methods are in use and their numbers are not comparable

A whole blood sample protected from light, ideally fasting and before any supplement is started. Sent to a specialist laboratory.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.