Differences in urinary albumin detected by four immunoassays and high-performance liquid chromatography.
OBJECTIVE
To compare the analysis of urinary albumin from diabetic patients by four conventional immunoassays including radioimmunoassay (RIA), immunonephelometry (IN), and two different methods of immunoturbidimetry (IT), as well as by high-performance liquid chromatography (HPLC).


METHODS
Urines were collected over a 24-h period and stored at -20 degrees C until assay. Urinary albumin concentration was determined by an in-house RIA, by IN using a Beckman Array Analyser with reagents from Beckman Diagnostics (Sydney, Australia), by IT using a Dade-Behring Turbitimer with reagents from Dade-Behring (Marburg, Germany), by IT using a Dade-Behring Dimension R x L Chemistry Analyser with reagents from DiaSorin (Stillwater, OK, USA), and by HPLC using a Zorbax Bio series preparative GF-250 column. Regression lines were calculated using a least squares method to determine the correlation between the assays studied. Bland-Altman bias plots including limits of agreement were also calculated.


RESULTS
The correlation coefficients calculated were high (>0.85) indicating a strong linear relationship between all assays studied. The slopes calculated for the comparisons demonstrate that each assay can vary from one another (up to threefold) and have a slope significantly different from an ideal slope of 1 (P < 0.001). These results were confirmed by Bland-Altman bias plots and calculation of the limits of agreement that were all large.


CONCLUSIONS
At this time, there is no global standard by which urinary albumin assays may be standardized. This study suggests the need for such standards.
Comper
Wayne D
WD
Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia. wayne.comper@med.monash.edu.au
Jerums
George
G
Osicka
Tanya M
TM
D000418:Albumins / Q000378:metabolism*; D000419:Albuminuria / Q000652:urine*; D002624:Chemistry, Clinical / Q000379:methods; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003928:Diabetic Nephropathies / Q000175:diagnosis* / Q000652:urine; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods; D008297:Male; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D000418:Albumins