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OBJECTIVE: Electrospray ionization-tandem mass spectrometry (ESI-MS/MS) is increasingly used in newborn screening programs. Acylcarnitine profiles from dried blood spots (DBS) are used to detect fatty acid oxidation disorders, carnitine cycle disorders, and organic acidurias. Stored dried blood is also a valuable source for postmortem investigations to unravel the cause of unexplained death in early childhood. However, diagnostic uncertainties arising from the unknown stability of acylcarnitines and free carnitine during prolonged storage have not yet been studied in a systematic manner. METHODS: Whole blood spiked with acylcarnitines was stored either at -18 degrees C or at room temperature up to 1000 days. At regular time intervals 3.2 mm spots of these samples were extracted with 150 microL of methanol. Free carnitine and acylcarnitines were converted to their corresponding butyl esters and analyzed by ESI-MS/MS. RESULTS: At -18 degrees C acylcarnitines are stable for at least 330 days. If stored for prolonged periods at room temperature (>14 days), acylcarnitines are hydrolyzed to free carnitine and the corresponding fatty acids. The velocity of decay is logarithmic and depends on the chain length of the acylcarnitines. Short-chain acylcarnitines hydrolyze quicker than long-chain acylcarnitines. CONCLUSION: The data indicate that stored filter cards should only be used for retrospective quantitation of acylcarnitines if appropriate correction for sample decay during storage is applied. Free carnitine increases upon storage but can reliably be quantitated under standardized derivatization conditions. Furthermore, carnitine transporter (OCTN2) deficiency can reliably be diagnosed by examining acylcarnitine profiles, which can supplement free carnitine levels as a discriminatory marker.

Newborn screening programs use whole blood dried on filter paper as the standard specimen. Metabolites are reasonably stable and can easily be sent to screening laboratories by regular mail. The recommended sample collection procedure is to spot native blood without anticoagulants onto the filter paper, because anticoagulants can interfere with the different laboratory methods. However, visual examination of the blood spots cannot always detect contamination. In this study, whole blood was drawn by venous puncture from a healthy volunteer, spiked with the corresponding metabolites and EDTA, and spotted onto filter paper. TSH and 17alpha-hydroxyprogesterone were determined by time resolved fluoroimmunoassays with the AutoDelfia system. Total galactose, biotinidase activity, and galactose-1-phosphate uridyltransferase activity were measured photometrically or fluorometrically. Succinyl acetone was estimated indirectly through the inhibition of porphobilinogen synthase activity (PBGS assay). EDTA, amino acids, and acylcarnitines were converted to the corresponding butyl esters, after extraction with methanol, and analysed by LC-MS/MS. EDTA contamination gives falsely elevated 17-OHP values and falsely reduced TSH and PBGS values. The inclusion of an EDTA determination in routine screening revealed that at least 0.06% of newborn screening samples were contaminated with EDTA. In conclusion, non-conformity during the pre-analytical phase is a source of false positive and false negative screening results. Determination of EDTA from NBS blood spots can reliably identify these samples and prevent screening errors.

The new genetic screening processor for newborn screening (GSP™) from PerkinElmer was extensively tested under routine conditions. The GSP is intended to fully process all newborn screening tests, apart from tandem mass spectrometry. For our evaluation we used all so far available tests for the GSP (TSH, 17-OHP, IRT, total-T4 and GALT). For all 5 tests we have determined specificity, limit of detection (LOD), limit of quantitation (LOQ), intra- and inter-assay variation, recovery, influence of EDTA and on-board stability of the reagents. Results were also compared with AutoDelfia and the Astoria Pacific Spot Check System (GALT). LOD and LOQ were 0.38 and 0.45 mU L−1 (blood) for TSH, 1.30 and 3.25 nmol L−1 (serum) for T4, 0.35 and 0.55 nmol L−1 (blood) for 17-OHP, 0.85 and 1.58 ng mL−1 (blood) for IRT and 2.6 and 3.6 U dL−1 (blood) for GALT. Mean recovery was 97.8–107.1%: intra-assay CVs 2.5–8.9; inter-assay CVs 5.7–11.0. On board stability was >37 days for the immunoassay. The dissolved GALT reagent is not stable at 4 °C, however if the reagent is removed from the GSP and stored at −18 °C, it is stable for 11 days. On board stability of the inducer is >140 days. The GSP is suitable for routine newborn screening. Compared to AutoDelfia, additional control procedures were included which increase the reliability of the system.

BACKGROUND Electrospray ionization–tandem mass spectrometry (ESI-MS/MS) has been used in the Bavarian newborn screening (NBS) program since 1999. The use of ESI-MS/MS has led to the inclusion of isovaleric acidemia (IVA) into NBS. We retrospectively evaluated data on more than 1.6 million newborns screened during 9.5 years. METHODS Acylcarnitines from whole blood spotted on filter paper were converted to their corresponding butyl esters, and the samples were analyzed by use of ESI-MS/MS with stable isotope labeled internal standards. RESULTS A total of 24 individuals with IVA were detected by use of a multiparametric threshold criteria panel including isovalerylcarnitine (C5) and the ratios of C5 to octanoyl-, butyryl-, and propionylcarnitine. A cutoff set at the 99.99th percentile for isolated C5 or at the 99th percentile for C5 plus at least 2 ratios resulted in a positive predictive value for IVA screening of 7.0% and an overall recall rate of 0.024%. Adjusted reference ranges for age and birth weight were applied, and the incidence of IVA in the study population was calculated to be 1 in 67 000. Missed cases were not brought to our attention. IVA was also detectable in cord blood and early postnatal blood samples. CONCLUSIONS IVA can be reliably detected in NBS through acylcarnitine analysis in dried blood spots by using multiparametric threshold criteria. Further improvement (positive predictive value 13.0%, recall rate 0.01%) can be achieved by using more stringent recall criteria. In view of the potentially life-threatening natural course of IVA in early life, presymptomatic diagnosis may thus prevent mortality and morbidity.

Maple syrup urine disease (MSUD) is an autosomal recessive inherited disorder caused by the deficiency of the branched-chain 2-oxo acid dehydrogenase (BCOA-DH) complex. The worldwide incidence is approximately 1 in 185,000. MSUD is integrated in many "expanded" newborn screening (NBS) programs that use electrospray ionization tandem mass spectrometry (ESI-MS/MS). Elevated leucine, isoleucine, and alloisoleucine in the dried blood samples (DBS) of newborns are diagnostic parameters. However, with the applied method, it is not possible to distinguish the amino acids from each other, and also not from the other isobaric amino acid, hydroxyproline. While the branched chain amino acids (BCAA) leucine, isoleucine, and alloisoleucine are no diagnostic problem, because they are all elevated in MSUD patients, and, rather, increase the diagnostic sensitivity and specificity, hydroxyproline may cause false-positive screening results. Hydroxyproline is elevated in the benign familial condition hyperhydroxyprolinemia, which needs no medical intervention. The detection of cases with hyperhydroxyprolinemia have formerly been reported from screening programs that used thin-layer chromatography for phenylketonuria (PKU) screening, and, recently, two more cases have been reported, detected by ESI-MS/MS-based NBS. However, the detection of non-diseases is a heavy burden for screening programs and should be avoided if possible. With optimal settings for the quantitation of BCAAs and interpretation rules, elevated hydroxyproline should not cause false-positive screening results.