Carbamylation of albumin is a cause for discrepancies between albumin assays

• Published in: Clinica chimica acta 2014-07, Vol.434, p.6-10
• Main Authors: Kok, Maarten B., Tegelaers, Frans P.W., van Dam, Bastiaan, van Rijn, Jan L.M.L., van Pelt, Johannes
• Format: Article
• Language: English
• Subjects: Albumin; BCG; BCP; Bromcresol Green - chemistry; Bromcresol Purple - chemistry; Bromocresol; Carbamylation; Hemodialysis; Humans; Nephelometry and Turbidimetry - methods; Quality Control; Serum Albumin - chemistry
• ISSN: 0009-8981; 1873-3492
• DOI: 10.1016/j.cca.2014.03.035

Several investigators have reported discrepancies between the bromocresol-purple (BCP), bromocresol-green (BCG) and immunonephelometric (INP) assays in dialysis patients. This study compared the abovementioned assays and investigated whether hemodialysis itself or carbamylation of albumin is the cause for this discrepancy. Samples obtained from hemodialysis patients were analyzed by BCP, BCG and INP. Furthermore, albumin was carbamylated in vitro using isocyanate. Isocyanate converts lysine to homocitrulline. No differences were observed between samples of the pre- and post-hemodialysis groups for BCP. In the control group, BCG averaged 6g/L higher than INP. BCP did not statistically deviate from INP. In the dialysis group BCG averaged 5g/L higher when compared to INP, whereas BCP averaged 2g/L lower. BCP was affected by carbamylation of albumin. BCG and INP measurements were affected to a much lesser extent. Homocitrulline content of hydrolysates was increased in both the carbamylated albumin as well as in the dialysis population. In a hemodialysis population albumin concentrations are not consistently estimated by both BCG and BCP methods. Relative to INP measurements BCG overestimates the albumin concentration (4–10g/L), whereas BCP leads to an underestimation (0–4g/L). Carbamylation of albumin is the main attributor to the discrepancy found with BCP. •Carbamylation causes discrepancies between assays for measuring albumin.•The BCP method for measuring albumin is affected by carbamylation.•Immunephelometry and BCG for measuring albumin are unaffected by carbamylation.•The BCP method is unsuitable for measuring albumin for patients with ESRD.•Carbamylation of albumin may lead to the prescription of more expensive drugs.