Moderate
Vitamin B12 / Folate
Both are required for DNA synthesis and neurological function, and deficiency in either produces macrocytic anaemia and, if it runs long enough, irreversible neurological damage. The case for testing rests almost entirely on who is being tested rather than on the test itself.
Why it grades Moderate
Well-established diagnostic tests within a macrocytic anaemia or neuropathy workup. Deficiency is common in the elderly, in vegans and vegetarians, after bariatric surgery, and with long-term metformin or proton-pump inhibitor use. Routine universal screening of asymptomatic, low-risk young adults is not guideline-recommended.