Neonatal Blood Carnitine Concentrations: Normative Data by Electrospray Tandem Mass Spectometry

Abstract

Despite a number of published reports, there is limited information about carnitine metabolism in the newborn. To establish normative data, we analyzed whole-blood carnitine concentrations in 24,644 newborns at age 1.85 Ϯ 0.95 d and umbilical cord whole blood and plasma carnitine concentrations in 50 full-term newborns. Total carnitine (TC), free carnitine (FC), and acylcarnitine (AC) were measured by electrospray tandem mass spectrometry. AC/FC ratios were derived from these measurements. The entire cohort was stratified according to TC values into a middle TC group representing 90% of the population and lower and upper TC groups representing 5% of the population, respectively. Normative data were derived from the middle TC group of full-term infants (N ϭ 19,595). TC was 72.42 Ϯ 20.75 M, FC was 44.94 Ϯ 14.99 M, AC was 27.48 Ϯ 8.05 M, and AC/FC ratio was 0.64 Ϯ 0.19 (ϮSD). These values differed significantly from umbilical cord whole blood TC values of 31.27 Ϯ 10.54 M determined in 50 samples. No meaningful correlation was found between TC and gestational age or birth weight in any group. In controlled analyses, prematurity was not associated with TC levels, whereas low birth weight (Ͻ2500 g) and male sex were significantly associated with higher TC levels. The association of low birth weight with higher TC values may be related to decreased tissue carnitine uptake. The sex effect may be related to hormonal influences on carnitine metabolism. Our study provides normative data of carnitine values measured by the highly precise method of electrospray tandem mass spectrometry in a large cohort of newborns and provides the basis for future studies of carnitine metabolism in health and disease states during the neonatal period. Abbreviations MS-MS, electrospray tandem mass spectrometry TC, total carnitine FC, free carnitine AC, acylcarnitine RBC, red blood cells OR, Odds ratio CI, 95% confidence interval RE, radioenzyme L-Carnitine serves as a carrier for acyl groups across the mitochondrial membrane. It is essential for the membrane transport and subsequent intramitochondrial ␤-oxidation of long-chain fatty acids and for the modulation of CoA homeostasis (1, 2). Adequate tissue levels of carnitine are crucial in the neonatal period, because mitochondrial oxidation of fatty acids is essential for the production of energy in newborns (3-6).L-Carnitine is derived mainly from exogenous sources and in part from endogenous synthesis (1). The main source of carnitine in the fetus seems to be transplacental transfer (4,7,8) and in the newborn seems to be breast milk or carnitine-supplemented formulas (3, 9 -11). Endogenous synthesis plays a minor role in early life because the activity of ␥-butyrobetaine hydroxylase, the enzyme necessary for carnitine synthesis, is very low (12).In tissues and body fluids, carnitine is present in free and esterified forms. The sum of free carnitine (FC) and acylcarnitine (AC) equals total carnitine (TC). The fraction of esterified carnitine varies depending on the tissue and on the metaboli...

Analysis and interpretation of acylcarnitine profiles in dried blood spot and plasma of preterm and full-term newborns

“…The levels of C 14 and C 16 were lower in plasma than in DBS. The differences related to the contribution of long-chain ACs of the erythrocyte membranes (8).…”

“…AC concentrations vary with birth weight (BW), gestational age (GA), and age at the time of collection (8). As reported previously (9), premature infants have different mean values from term-born infants due to their lower birth weight and to treatments administered at the neonatal intensive care unit (NICU), so different cutoffs would need to be defined to reduce the risk of false-positive cases.…”

Use of Tandem Mass Spectrometry for Multianalyte Screening of Dried Blood Specimens from Newborns

“…l-Carnitine (FC) produces fragments at both m/z 85 and 103 (49 ). Generally, the fragment at m/z 103 includes the aliphatic hydroxyl group (ϪOH), which requires higher energy to fragment and produce the ion at m/z 85 and thus is generally present at higher abundance.…”

Long-Term Stability of Amino Acids and Acylcarnitines in Dried Blood Spots

“…Subsequently, we added 100 L methanol extraction solution, mixed with stable isotopedeuterated internal standards (CIL). 13 C-Arg-HCl 2.5 mol/L. The plate was sealed and mixed.…”

“…The concentrations of metabolites in affected infants exceed the respective population-dependent cutoff limits. In addition, metabolite concentrations depend on metabolic status, dietary intake (2 ), and maturity of the infants (13,14 ), which may pose a diagnostic challenge. Time-dependent degradation of metabolites during long-term storage of dried blood filter cards may contribute to metabolite variability.…”