Reference interval of methylmalonic acid concentrations in dried blood spots of healthy, term newborns to facilitate neonatal screening of vitamin B12 deficiency.

OBJECTIVES

Unrecognized vitamin B12 (B-12) deficiency in early infancy can lead to poor development of the child. Methylmalonic acid (MMA) is the most specific functional biomarker of B-12 status. To facilitate timely diagnosis and treatment of neonatal B-12 deficiency, the objective of this study was to calculate a reference interval of MMA in dried blood spots (DBSs) of healthy, term newborns.

DESIGN AND METHODS

MMA was quantified in 160 newborn DBSs, routinely collected for newborn screening, using LC-MS/MS. The reference interval of DBS MMA was calculated according to current guidelines (CLSI EP28-A3c). The effect of storage at room temperature on DBS MMA concentrations was determined.

RESULTS

The mean DBS MMA concentration of 160 healthy, term newborns was 16.8pmol (95% CI: 15.9-17.6pmol)/8-mm spot. The reference interval (2.5th to 97.5th percentile) for MMA was 9.89 to 29.3pmol/8-mm spot (0.450 to 1.33μmol/L whole blood). DBS MMA concentrations correlated positively (p<0.005) with storage time at room temperature. DBS MMA concentrations of children with methylmalonic acidemia (n=4) were above the upper limit of the reference interval.

CONCLUSIONS

This is the first study to present a reference interval for DBS MMA of healthy, term newborns utilizing a new highly sensitive MMA method. Analysis of DBS MMA collected during newborn screening may have the potential to identify newborns with acquired B-12 deficiency. Newborn DBS MMA concentrations increase with storage at room temperature, therefore, sample storage has to be monitored for evaluation of DBS MMA data.