Carbamylation of albumin is a cause for discrepancies between albumin assays.
BACKGROUND
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.


METHODS
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.


RESULTS
No differences were observed between samples of the pre- and post-hemodialysis groups for BCP. In the control group, BCG averaged 6 g/L higher than INP. BCP did not statistically deviate from INP. In the dialysis group BCG averaged 5 g/L higher when compared to INP, whereas BCP averaged 2 g/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.


CONCLUSIONS
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 (4-10 g/L), whereas BCP leads to an underestimation (0-4 g/L). Carbamylation of albumin is the main attributor to the discrepancy found with BCP.
Medical Center Alkmaar, Laboratory of Clinical Chemistry, Hematology and Immunology, Alkmaar, The Netherlands. Electronic address: maarten.b.kok@gmail.com.
Maarten B
MB
Kok
Medical Center Alkmaar, Laboratory of Clinical Chemistry, Hematology and Immunology, Alkmaar, The Netherlands.
Frans P W
FP
Tegelaers
Department of Internal Medicine, Alkmaar, The Netherlands.
Bastiaan
B
van Dam
Westfriesgasthuis, Laboratory of Clinical Chemistry, Hoorn, The Netherlands.
Jan L M L
JL
van Rijn
Medical Center Alkmaar, Laboratory of Clinical Chemistry, Hematology and Immunology, Alkmaar, The Netherlands.
Johannes
J
van Pelt
D001961:Bromcresol Green / Q000737:chemistry*; D001962:Bromcresol Purple / Q000737:chemistry*; D006801:Humans; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D011786:Quality Control; D012709:Serum Albumin / Q000737:chemistry*
D012709:Serum Albumin; D001962:Bromcresol Purple; D001961:Bromcresol Green
Albumin; BCG; BCP; Bromocresol; Carbamylation; Hemodialysis