Analytical variance and definition of a reference change as a function of calcium concentration.

Abstract

Using data from the Centers for Disease Control (CDC) Proficiency Testing (PT) Surveys, we obtained estimates of repeatability (intralaboratory variability between results on the same material) and reproducibility (interlaboratory variability between results on the same material) for the Technicon SMA 6 (or 12/60) and SMAC 1 (or II) systems used with cresolphthalein complexone methodology to measure serum calcium. The two systems were comparable in terms of short-term (within-day) repeatability, long-term (three to six months) repeatability, short-term (one to two weeks) reproducibility, and long-term (three to six months) reproducibility. The long-term repeatability was essentially the same as the long-term reproducibility. Short-term repeatability, long-term repeatability, and long-term reproducibility increased linearly with increased calcium concentration over the range 1.75 to 2.95 mmol/L; short-term reproducibility showed no significant change over this range. The effect of analytical variance on the definition of a reference change in semiannual calcium measurements was demonstrated.

Serum biochemistry and hematology values and hemoglobin electrophoresis in Persian squirrels (Sciurus anomalus)

“…Calcium concentration was measured by the o‐cresophthalein complexone 6. Urea concentration was measured by using a diacetylmonoxime reagent and the results converted to urea nitrogen by multiplying by 0.467 7.…”

Variation in Laboratory Reports: Causes other than Laboratory Error

“…So the changes in Glucose greater than 17% are significant and changes less than this is expected due to the inherent random sources of variation. However, to minimize confounding effects, analytical imprecision CV A should be less than one-half the within-subject biological variation CV I, 1 for example CV A (2.7%) is less than ½ of CV I i.e. 5.6%.…”

“…The trend in cross-checking and seeking the second opinion in laboratory results is increasing the dilemma rather than enforcing the results, as most of the time the reports released by two laboratories for the same individual (reproducibility) is different and even the reports released by the same laboratory (repeatability) shows variations. 1 Shortterm (within-day to two weeks) repeatability and short-term reproducibility are more of a concern than long terms (three to six months). This disparity in the results from clinical laboratories has always been an issue and might cause confusion to diagnose, treat and monitor disease.…”