Clinical Chemistry, Vol 22, 1855-1861, Copyright © 1976 by American Association for Clinical Chemistry

Correlation of selected serum constitutents: 2. Consistency of intra- individual correlation values, means, and variances during four months

P Winkel and BE Statland

We examined whether inter-individual differences in correlation coefficients previously found among subjects truly reflect consistent inter-individual differences or are time-related within an individual. The consitutents studied in this investigation were (a) the enzmes aspartate aminotransferase, alkaline phosphatase, and lactate dehydrogenase; and (b) the non=protein nitrogen-containing constituents urea, uric acid, and creatinine. Ten healthy women were each subjected to 15 venipunctures over a five-week period (Series I), and, after a two-month interval, were again subjected to 15 venipunctures over a second five-week period (Series II). Before statistical analysis, the data were corrected for the batch-to-batch (day-to-day) arnalytical variation. There was a signiificant (P less than .05) change in the covariance structure (variances or correlation coefficients, or both) between the two series in four of the 10 subjects for the combination of enzymes, and in three other subjects for the combination of nonprotein nitrogen constitutents. Although we found a significant (P lees than .05) average intra-individual variation in the mean values from series to series in the cases of the three enzymes and urea, the magnitude of the inter-series variation in means was relatively small. CV's were: alkaline phosphatase, 3.4%; lactate dehydrogenase, 2.3+; aspartate aminotransferase, 3.3%; urea, 5.0%; uric acid, 1.0%; and creatinine, 1.2%.