A person with constant fatigue and lethargy should undergo blood tests, B12 levels, folate, homocysteine, ferritin and thyroid levels, nutritionist Nazvanova told TASS.
If a B6 deficiency is suspected, organic acids in the urine should be tested. You can also check the condition of the stomach lining, microbiota and the presence of invasions. However, it is not necessary to test for all vitamins in sequence, she noted.