Performance of serum and dried blood spot acylcarnitine profiles for detection of fatty acid ß-oxidation disorders in adult patients with rhabdomyolysis.

BACKGROUND: Plasma/serum and dried blood spot (DBS) acylcarnitine profiles (ACPs) are key to the diagnosis of mitochondrial fatty acid ß-oxidation disorders (FAODs). Despite their significant clinical applications, limited published data exists to compare their sensitivities and specificities. We retrospectively evaluated these two methods in adult patients with a history of rhabdomyolysis; investigated for an underlying FAOD. METHODS: A retrospective study was completed for adult patients (investigated between 2003 and 2011) meeting the inclusion criteria of a history of recurrent rhabdomyolysis or one episode of rhabdomyolysis with a history of exercise intolerance. All subjects underwent investigations for an underlying FAOD including DBS and serum ACP analysis concurrently collected during a symptom-free period, and skin biopsy for cultured fibroblast fatty acid oxidation studies or enzyme activity measurement, as indicated, with or without molecular confirmation. Their medical records were reviewed, and the performance of the two methods were compared. RESULTS: Seven out of 31 subjects (22.6 %) were diagnosed with an underlying FAOD. Long chain acylcarnitines were more markedly elevated in serum samples from confirmed CPTII cases (n = 4) as compared to matched DBS profiles. The sensitivity and specificity of DBS ACP was 71.4 % (95 % CI, 0.30-0.95) and 100 % (95 % CI, 0.79-1.00), respectively, compared to a sensitivity of 100 % (95 % CI, 0.56-1.00) and a specificity of 94.7 % (95 % CI, 0.72-1.00) for serum ACP. CONCLUSION: FAODs appear to be a common cause of recurrent rhabdomyolysis or rhabdomyolysis with a history of exercise induced myalgia. At least historically, FAODs maybe underdiagnosed in adults with rhabdomyolysis. This study suggests that serum ACP might be more sensitive than DBS ACP for detection of an underlying FAOD in adults with rhabdomyolysis while asymptomatic.

Interlaboratory comparison study of serum total testosterone [corrected] measurements performed by mass spectrometry methods.

BACKGROUND: Though mass spectrometry (MS) assays are increasingly used for routine clinical measurements of serum total testosterone (TT), information about the variability of results is limited. This study assessed the variability of TT measurement results from routine MS assays. METHODS: Twenty serum samples (12 females, 8 males) were analyzed on 2 days by seven high performance liquid chromatography (HPLC), and one gas chromatography (GC)-tandem mass spectrometry (HPLC-MS/MS, GC-MS/MS) assays. Two samples (male and female) were provided in five replicates to assess the within-run variability. Results were compared against those obtained at National Institute of Standards and Technology (NIST). The within- and between-laboratory variability was assessed for each sample. Comparisons to the NIST results were performed using bias plot and Deming regression analysis. RESULTS: The overall coefficient of variation of the results obtained with MS assays was <15%CV at >1.53 nmol/L and <34%CV at 0.3 nmol/L. The between-assay variability was the major contributor to the overall variability. The assay precision was the highest (<3%CV) with assays using liquid-liquid extraction for sample preparation or GC-MS/MS. The mean percent difference to the reference assay was 11%. The slopes of Deming regression analysis of the MS assays were between 0.903 and 1.138 (correlation coefficient: >0.996). TT concentrations for one assay were above the measurement range. CONCLUSIONS: The variability of TT measurement results among MS assays is substantially smaller than that reported for immunoassays. The type of sample preparation may affect assay precision. Standardizing assays can further reduce the variability of measurement results.

Newborn screening for MCAD deficiency: experience of the first three years in British Columbia, Canada.

BACKGROUND: Medium Chain Acyl-CoA Dehydrogenase (MCAD) Deficiency is an autosomal recessive disorder of fatty acid oxidation, with potential fatal outcome. MCAD deficiency is diagnosed by acylcarnitine analysis on newborn screening blood spot cards by tandem mass spectrometry. Early diagnosis of MCAD and presymptomatic treatment can potentially reduce morbidity and mortality. OBJECTIVES: To evaluate incidence, clinical outcome, biochemical and molecular phenotype of MCAD cases detected in the first three years of newborn screening in British Columbia (BC). METHODS AND RESULTS: Medium chain length acylcarnitines, octanoylcarnitine (C8) and decanoylcarnitine (C10), were measured on newborn screening blood spot cards. Out of 121,000 live births, 17 newborns had C8 values above the screening cut-off of 0.38 umol/L. Ten newborns had elevated C8 on repeat cards and were investigated further. Both C8 and C8/C10 ratios remained abnormal in all confirmed MCAD cases. Positive predictive value of screening was 58% with no false negative results. Seven patients were homozygous for the common c.985A > G MCAD mutation and three others were compound heterozygous for the c.985A > G and a second mutation. Two novel mutations were identified (c.260T > C and c.382T > A). The estimated incidence of MCAD was approximately 1:12,000 live births. Upon frequent feeding and carnitine supplementation, none of the patients had metabolic crises or adverse outcomes. CONCLUSION: Frequency of MCAD in BC is comparable to reports from other newborn screening programs. Persistence of elevated C8 levels and C8/C10 ratios in confirmed MCAD cases suggest that these are sensitive markers for newborn screening. Early detection and treatment have successfully prevented adverse health outcomes in patients with MCAD.