Evaluation of the Performance of a Micromethod for Measuring Urinary Iodine by Using Six Sigma Quality Metrics

BACKGROUND: The urinary iodine micromethod (UIMM) is a modification of the conventional method and its performance needs evaluation. METHODS: UIMM performance was evaluated using the method validation and 2008 Iodine Deficiency Disorders survey data obtained from four urinary iodine (UI) laboratories. Method acceptability tests and Sigma quality metrics were determined using total allowable errors (TEas) set by two external quality assurance (EQA) providers. RESULTS: UIMM obeyed various method acceptability test criteria with some discrepancies at low concentrations. Method validation data calculated against the UI Quality Program (TUIQP) TEas showed that the Sigma metrics were at 2.75, 1.80, and 3.80 for 51+/-15.50 microg/L, 108+/-32.40 microg/L, and 149+/-38.60 microg/L UI, respectively. External quality control (EQC) data showed that the performance of the laboratories was within Sigma metrics of 0.85-1.12, 1.57-4.36, and 1.46-4.98 at 46.91+/-7.05 microg/L, 135.14+/-13.53 microg/L, and 238.58+/-17.90 microg/L, respectively. No laboratory showed a calculated total error (TEcalc)

Screening method for detection of immediate amino acid decarboxylases - producing bacteria implicated in food poisoning

Assessment of amino acid decarboxylase activity can be conducted using tubed broth or plated agar. In this study, the test was carried out in microtitre plates containing lysine, ornithine, arginine, tyrosine, tryptophan, phenylalanine or histidine as biogenic amine precursors. Møller decarboxylase base broth (MDB) with or without 1% of a known amino acid were added to wells of a 96 well-microtitre plate. The wells were inoculated with Escherichia coli, Klebsiella pneumoniae, Acinetobacter anitratus or Staphylococcus aureus to the final concentration of 6.0 x 107 cfu/ml and incubated at 35oC. The absorbance of the culture broth was read at 570 nm at 0, 1.0, 2.0, 3.0, 4.0, 5.5, 6.5 and 7.5 hour. Comparison of means of A’570 between 0 hour and a specified incubation time was determined statistically. Positive decarboxylase activities were detected in the media inoculated with E. coli and K. pneumoniae in less than 6 hours. The current method is suitable for immediate producers of amino acid decarboxylase enzymes. It costs less as it uses less amino acid and it has the potential to be used for screening aliquots of food materials for amino acid decarboxylase activities.

A cost-effective modified micromethod for measuring urine iodine.

A modified micromethod for measuring urine iodine was successfully established and validated. The micromethod showed good correlation with the method used by several World Health Organization (WHO) collaborative laboratories (y = 0.9342x + 4.6213; r = 0.962; p = 0.01; n = 50). The micromethod also showed good agreement when compared to the reference WHO method. The sensitivity of the assay was 13.809 ug/L (n = 8) and mean recoveries were 114, 103 and 106% at concentrations of 30, 40 and 50 ug/L (n = 3) respectively. At iodine concentrations of 51 +/- 15.5, 108 +/- 32.4 and 149 +/- 38.6 ug/L, intra-assay coefficient of variations (CVs) were 13%, 7% and 5% respectively (n = 20), and inter-assay CVs were 10%, 15% and 7% respectively (n = 10). The assay showed good linearity plot (y = 1.0407x + 60.451; r = 0.993; n = 3).