Stankeviciute N, Sabah S, Singh A, Shaykh M, Bakir AA, Arruda
JAL, Dunea G
Total urinary protein: dogma challenged
Am Soc Nephrol
J Am Soc Nephrol (abstract)
(Sep) 7:1343 1996
Measuring the excretion of urinary protein can have significant
prognostic implications in patients with kidney disease. It may also
impact some therapeutic decisions such as dietary prescription, use of
ACE inhibitors or antihypertensive agents. The causes of inaccurate
or imprecise results are legion and frustrating.
This study by Stankeviciute et al. focuses on those problems that are
due to the methodology employed to measure urinary albumin and
protein. Random urine samples from 61 patients were evaluated for
protein content using the Biorad dye binding assay in undialyzed and
dialyzed urine. Another method involved chromatographic separation of
the urinary albumin and protein, which were then each measured using
appropriate standards. With the average protein value, measured as
dye binding of dialyzed urine, representing 100%, chromatography
yielded a value of 141% and dye binding of undialyzed urine yielded
121 percent. The question remains: which of these values best
correlates with albuminuria? Albumin content was next measured using
radioimmunoassay as a "gold standard". The values for total urinary
protein from the above three methods were used to identify normal
urine specimens and those with microalbuminuria. Then the
radioimmunoassay values for albumin were used to identify false
positives and false negatives.
Using these parameters undialyzed urine gave a false positive and
false negative result 10% and 11% of the time, respectively.
Dialyzed urine gave a false positive and false negative result 2% and
18% of the time, respectively.
Comment: These false positive and negative rates are not
trivial. Unfortunately dialysis of urine specimens is labor intensive
- chromatography and radioimmunoassay prohibitively so. In addition,
in a clinical setting the increased accuracy of these latter
techniques may well be diluted by other sources of error, e.g.
collection or timing errors. Calculating the urinary protein to
creatinine ratio may obviate some of these latter errors. Greg
Cowell, M.D., University of Illinois at Chicago
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Am Soc Nephrol
Assessing renal function :
Urinary protein/albumin