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 16.8 pmol (95% CI: 15.9-17.6 pmol)/8-mm spot. The reference interval (2.5th to 97.5th percentile) for MMA was 9.89 to 29.3 pmol/8-mm spot (0.450 to 1.33 nmol/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. (C) 2016 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.