Discrepancies in Serum Albumin Measurements Vary by Dialysis Modality

Abstract

Background. Serum albumin level is an important prognostic marker in patients with chronic renal failure. However there are discrepancies in the methods of estimation of serum albumin. The objective of this study is to evaluate the magnitude of the discrepancy in the serum albumin levels as measured by Bromcresol Green (BCG) and Bromcresol Purple (BCP) dye methods in patients on hemodialysis (HD) and peritoneal dialysis (PD) and to ascertain the clinical determinants of the discrepancy (ΔSA = BCG-BCP; g/dL) in each of the modalities. Method. We measured serum and plasma albumin levels by BCG and BCP methods in 19 adult HD patients and 18 adult PD patients treated in the dialysis units of the University of Colorado Health Sciences Center. Similar measurements were performed in 10 normal adult subjects. In all groups, paired blood samples were taken to estimate the albumin in both serum and plasma. Nephelometry (NM) was subsequently performed on the serum of 13 of the HD patients, 14 of the PD patients, and each of the 10 normal subjects. Results. We found that for both the dye methods serum and plasma albumin levels are almost identical in each of the three subject groups. In the normal subjects serum albumin estimated by BCP is in good agreement with NM values but BCG overestimates the albumin levels. In the PD group the discrepancy between the BCG and BCP (ΔSA) is statistically significant with the BCG averaging 0.59 ± 0.12 g/dL more than the BCP. The BCG values are closer to those obtained by the “gold standard”, NM. In the HD group the ΔSA is significantly (p<0.001) less than in the PD group (0.34 ± 0.11 g/dL). As for PD, BCG values are closer to NM values. Increasing age, female gender, and higher dialysis adequacy are associated with higher ΔSA in the HD but not in the PD group. Utilizing linear regression analysis we developed equations for each dialysis modality to convert albumin measurements from one method to the other. Conclusion. We confirm that a discrepancy exists between the commonly used dye methods (BCG and BCP) for serum albumin estimation. This discrepancy is significantly lower in HD patients than in PD patients. Nephrologists should be aware of this discrepancy and appropriate corrections should be made during quality improvement analysis.