Are equally spaced specimen collections necessary to assess biological variation? Evidence from renal transplant recipients.

The established method for determining the components of biological variation (BV) requires equispaced time intervals between samplings. In a previous study, we determined BV in renal post transplantation patients, taking advantage of the samples obtained within their clinical treatment protocol (not necessarily equispaced). To confirm the validity of this practice, we sought to determine if the use of varying sampling intervals has an effect on the results obtained in such biological variation studies. The study included two phases: comparison of the results found with identical and non-identical sampling intervals and correlation between the within-subject BV and the length of the sampling interval. There were no differences in within-subject BV between the groups or correlations with sampling intervals for any of the constituents studied. We conclude that samples acquired within established clinical protocols for kidney transplant recipients can be used for estimating BV.