Making sense of laboratory tests of folate status: folate requirements to sustain normality.

Abstract

The first event in the sequence leading to nutrient deficiency is development of negative nutrient balance, i.e., nutrient utilization, requirement, catabolism, and excretion exceeds nutrient ingestion, absorption, and anabolism. Persistent negative nutrient balance produces a sequence of stages or degrees along a continuum of nutrient depletion which are not always clearly demarcated one from the next but show an increasing deficiency, usually marked by sequential appearance of various biochemical and clinical deficits. In the case of folate, the continuum from normality to folate-deficiency megaloblastic anemia begins with negative folate balance and proceeds through three sequential stages, or degrees, of folate depletion, each defined by the appearance of specific biochemical and/or hematologic markers (Table 1, Fig. 1).