Reliable and powerful laboratory markers of cobalamin deficiency in the newborn: plasma and urinary methylmalonic acid.

BACKGROUND

Diagnosing cobalamin deficiency is critical, given the high prevalence of cobalamin deficiency particularly in developing countries. Measuring serum cobalamin levels is of limited diagnostic sensitivity, in other words its specificity and sensitivity are low. The present study investigated the changes in the levels of metabolic markers - plasma homocysteine, plasma methylmalonic acid (MMA) and urinary MMA - of cobalamin metabolism.

METHODS

Plasma cobalamin and serum folic acid were studied in 206 pregnant women over the last four prenatal weeks. Plasma cobalamin, folic acid, homocysteine, MMA from umbilical cord blood and urinary MMA in newborns were studied.

RESULTS

Plasma cobalamin values were low in 66% of the mothers. There was a positive correlation between maternal and neonatal plasma cobalamin values (r = 0.72, p < 0.001). B12 was strongly inversely associated with plasma MMA, urine MMA and plasma homocysteine. To predict cobalamin deficiency, sensitivities of plasma MMA, urinary MMA and homocysteine were 96.4%, 95.6% and 88.2%, respectively. And positive predictive values (PPV) were 96.2%, 96.9% and 86% for plasma MMA, urinary MMA and plasma homocysteine levels, respectively.

CONCLUSION

Plasma MMA and urinary MMA B12 are the most robust markers of cobalamin deficiency. As a non-invasive method, urinary MMA is a sensitive method in demonstrating cobalamin deficiency in the newborn.