title: Stability of mean assay values of magnesium and iron in lyophilized quality control serum: a study based on data from the quality assurance service (QAS) of the College of American Pathologists.
abstract: Data from magnesium and iron analyses of pools of lyophilized quality control serum were used to evaluate stability of analyte mean values in the pre-reconstitution period. Information was received from laboratories in Regional Quality Control Programs between 1977 and 1981, using CAP Quality Assurance Service data processing. For magnesium, 28 of 41 (68%) pool-method combinations were stable, 11 (27%) showed decreases, and 2 (5%) showed increases. Decreases averaged 0.008 mg/dL/month (all methods). A pronounced effect of method (automated methylthymol blue) and year correlated with decreases in measurable magnesium. For iron, 45 of 56 (80%) pool-method combinations were stable, 8 (15%) showed decreases, and 3 (5%) showed increases. Decreases averaged 0.349 g/dL (all methods). In most cases, changes in measured concentrations are attributed to methodologic factors, rather than intrinsic changes in analyte concentrations.
mesh_terms: D001322:Autoanalysis / Q000592:standards; D004355:Drug Stability; D005612:Freeze Drying; D006801:Humans; D007501:Iron / Q000097:blood*; D008274:Magnesium / Q000097:blood*; D010338:Pathology, Clinical / Q000592:standards*; D012016:Reference Values; D012955:Societies, Medical; D013054:Spectrophotometry, Atomic / Q000592:standards; D014481:United States
chemical_list: D007501:Iron; D008274:Magnesium