Biological variation at long-term renal post-transplantation.

In laboratory testing the reference change value (RCV) is used to detect changes in a patient's clinical status, even before clinical signs are evident. In a previous study we determined the biological variation (BV) of a number of constituents during early post-transplantation in kidney recipients to calculate useful RCVs for this purpose. RCVs for creatinine and urate were identified as the most suitable and were different from those calculated from the normal population. The aim of the current study was to determine the BV components at long-term following renal transplantation to predict potential crises in transplant recipients who have been stable for a number of years. BV components for creatinine and urate were calculated in a new group of 40 kidney transplanted patients (26 men and 14 women, 29-71 years old) who had been stable for period of 4 to 7 years following transplantation (long-term post-TR group). An average of 8 samples per patient was obtained during a period of 1-2 years. Results were compared with those from our described group of recently transplanted patients (short-term post-TR group). There were no statistically significant differences between the groups with regard to within-subject variation or within-subject plus analytical variation (CVI+A) for any of the constituents studied. Distribution of CVI+A values in long-term post-TR was comparable to that of short-term post-TR values. Independence between creatinine and urate was maintained at long-term. The fact that BV components for creatinine and urate were similar in short- and long-term post-TR and that independence was maintained implies that the short-term post-TR RCV can also be applied in long-term post-TR patients. The RCV for predicting crises in this population represents an optimization of laboratory reporting and could be a valuable tool for clinical decision making.