COMPARISON OF THE DEOXYURIDINE SUPPRESSION TEST WITH SERUM LEVELS OF METHYLMALONIC ACID AND HOMOCYSTEINE IN MILD COBALAMIN DEFICIENCY

Both the deoxyuridine suppression test (dUST) and the cobalamin-depend ent metabolites, methylmalonic acid (MMA) and homocysteine, are valuab le tools for identifying clinical cobalamin deficiency. Examination of these metabolic changes in mild or marginal deficiency can provide us eful comparisons of diagnostic frequencies and sensitivities and help define the sequence of metabolic changes in early deficiency, These te sts were therefore compared directly with each other in 50 patients wi th low cobalamin levels and few or no obvious signs of deficiency. Ser um homocysteine (P = 0.0003) and MMA levels (P = 0.0004) correlated wi th dUST results. However, the dUST results were abnormal significantly more often (38/50 patients) when matched against levels of homocystei ne (25 abnormal results of 50; P = 0.007) or MMA (20/50; P = 0.008). A bnormalities of one or both serum metabolite levels (30/50 patients) o ccurred almost as often as dUST abnormalities (P = 0.059). Metabolite levels, even when originally 'normal', fell with cobalamin therapy in many cases, The results indicate that both the dUST and serum metaboli te levels become abnormal before macrocytic anaemia develops in mild c obalamin deficiency. The dUST appears to be the most frequently abnorm al of the tests; metabolite levels appear to rise almost concurrently but they do not become diagnostically abnormal as soon.