A new test method for biochemical analysis of plasmalogens in dried blood spots and erythrocytes from patients with peroxisomal disorders.

Measurement of plasmalogens is useful for the biochemical diagnosis of rhizomelic chondrodysplasia punctata (RCDP) and is also informative for Zellweger spectrum disorders (ZSD). We have developed a test method for the simultaneous quantitation of C16:0, C18:0, and C018:1 plasmalogen (PG) species and their corresponding fatty acids (FAs) in dried blood spots (DBS) and erythrocytes (RBC) by using capillary gas chromatography-mass spectrometry. Normal reference ranges for measured markers and 10 calculated ratios were established by the analysis of 720 and 473 unaffected DBS and RBC samples, respectively. Determination of preliminary disease ranges was made by using 45 samples from 43 unique patients: RCDP type 1 (DBS: 1 mild, 17 severe; RBC: 1 mild, 6 severe), RCDP type 2 (DBS: 2 mild, 1 severe; RBC: 2 severe), RCDP type 3 (DBS: 1 severe), RCDP type 4 (RBC: 2 severe), and ZSD (DBS: 3 severe; RBC: 2 mild, 7 severe). Postanalytical interpretive tools in Collaborative Laboratory Integrated Reports (CLIR) were used to generate an integrated score and a likelihood of disease. In conjunction with a review of clinical phenotype, phytanic acid, and very long-chain FA test results, the CLIR analysis allowed for differentiation between RCDP and ZSD. Data will continue to be gathered to improve CLIR analysis as more samples from affected patients with variable disease severity are analyzed. The addition of DBS analysis of PGs may allow for at-home specimen collection and second-tier testing for newborn screening programs.

Reliable, Rapid, and Robust Speciation of Arsenic in Urine by IC-ICP-MS.

BACKGROUND: Arsenic is a naturally occurring element with varying species and levels of toxicity. Inorganic arsenic (e.g., arsenite (AsIII) and arsenate (AsV)) are toxic, while its metabolites (e.g., monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA)) are less toxic). Symptoms of exposure can include headaches, confusion, diarrhea, and drowsiness. As these symptoms overlap with many other conditions, arsenic exposure can often be overlooked as a cause. Arsenic toxicity may be treated with chelation and/or electrolyte replacement therapy. However, treatment is not without risks and is unnecessary for exposure to organic (nontoxic) forms of arsenic. This makes screening and differentiation of arsenic important for clinical testing. METHOD: An IC-ICP-MS method was developed using a Dionex 5000 with ion exchange chromatography for separation and iCAP Q for detection. Nontoxic species are arsenobetaine and arsenocholine, and toxic species are AsIII, DMA, MMA, and AsV. RESULTS: Precision, linearity, and specificity studies produced acceptable results. For accuracy, proficiency testing and method comparison samples were analyzed and produced acceptable results. Carryover studies demonstrated single species carryover from the diluter at levels of 500 µg/L, which can be avoided by analysis rules in the standard operating procedure. Limit of detection studies yielded a lower limit of quantitation of 1 µg/L per species. CONCLUSIONS: Here, we present a rapid and reliable method for quantifying and differentiating toxic and nontoxic forms of arsenic to allow for swift and appropriate management of patients with exposure.