Albumin as an outcome measure in haemodialysis in patients: the effect of variation in assay method

Background. Serum/plasma albumin is an important predictor of future mortal ity/morbidity in haemodialysis (PID) patients and has been proposed as an i mportant audit measure. Different methods of albumin assay give different r esults and the bias between methods may be greater in renal failure patient s. Methods. Albumin concentration in plasma was measured by three methods, two dye-binding methods (bromocresol green(BCG) and bromocresol purple(BCP)) a nd an immuno-turbidimetric (ITM) method, in 143 HD patients (group I) and 4 9 non-renal patients (group II). Comparisons were made between means, varia tion in differences across a range of albumin concentrations and on the per centage of patients within the normal range. Results. In HD patients (group I), BCG overestimated plasma albumin compare d with the other two methods. The difference could be as much as 10 g/l and was more marked in hypoalbuminaemic patients. The BCP method gave results closer to the ITM method, particularly in HD patients. These differences we re less marked in group II patients but both methods overestimated albumin compared with the ITM method. Using the BCG local laboratory normal range, 84% of HD patients had plasma albumin concentrations within the normal rang e but this fell to 57% if the BCP results were used. Conclusions. The method for determining albumin concentration has a marked effect on the results particularly in HD patients. BCG, the most commonly u sed method, gives higher results than other methods and correlates poorly w ith an immunological method. These differences make comparative audit betwe en nephrology units difficult and have implications for other biochemical v ariables and other specialties.