Can total urinary protein measurements predict microalbuminuria?

Evaluation of a commercial in-house test kit for the semi-quantitative assessment of microalbuminuria in cats

Proteinuria was assessed in 100 randomly selected sick cats and 22 healthy cats by means of the urine protein:creatinine ratio, a traditional urine ‘dipstick’ and a commercial ELISA-based dipstick designed to detect microalbuminuria (MA) semi-quantitatively. In addition the repeatability and reproducibility of the MA test was assessed by comparing results of five replicate tests of 26 urine samples, interpreted by two different readers. Discrepancies existed in the replicate test result in 23 and 27% of the samples examined by reader 1 and 2, respectively, and on several occasions this discrepancy was between whether the sample was ‘positive’ or ‘negative’ for MA. The inter-reader agreement was good ( κ=0.75), but again discrepancies were noted and part of the reason for these problems appeared to be the necessary subjectivity in the interpretation of colour changes when reading test results. Proteinuria was significantly ( P≤0.014) more prevalent in the sick than the healthy cats with 36 and 9%, respectively, having detectable MA, 34 and 5%, respectively, having a urine protein to creatinine (UPC) ratio >0.5, and 84 and 9%, respectively, having positive urine protein dipstick analysis. There was a moderate significant correlation between UPC ratio and MA concentrations ( rs=0.68, P<0.0001). While 13/87 cats with a UPC ratio ≤0.5 had positive MA results, 10/84 cats with negative MA results had a UPC ratio >0.5, and none of these had evidence of lower urinary tract disease. This study confirmed that MA and proteinuria are commonly seen in cats with a variety of diseases, but they are not necessarily both elevated, and the UPC ratio can be elevated without an increase in MA results. Furthermore, some repeatability problems were demonstrated with the semi-quantitative MA test. These findings demonstrate that the semi-quantitative MA test should not be relied on as the sole determinant of proteinuria.

Evaluation of proteinuria in healthy living kidney donor candidates

BACKGROUND

Evaluation of living kidney donor candidates includes careful assessment for the presence or absence of kidney disease. Kidney donation has been considered to be at least relatively contraindicated if urinary total protein excretion is above the normal range. However, at the present time, there is no uniformly accepted level of urine total protein excretion that would exclude donation. Albumin excretion instead of total protein excretion as a criterion has not previously been evaluated.

MATERIALS AND METHODS

This was a prospective observational study over a 3-year period in a single tertiary care center designed to assess current selection criteria for kidney donation with respect to urine total protein and albumin excretion.

RESULTS

Twenty four percent (25 of 105) of healthy adult kidney donor candidates had elevated urinary total protein excretion rates (150 to 292 mg/24 h). Of these 105 candidates, 39 had simultaneous measurements of both urinary total protein and albumin. Although one-third (13/39) had elevated 24-hour urine total protein values, none had elevated urine albumin excretion.

CONCLUSION

Measurement of albumin, the most common single protein found in urine, appears to be helpful in the evaluation of proteinuria in donor candidates. Many healthy adult kidney donor candidates have mildly elevated total protein excretion but normal albumin excretion. We believe that such patients should not be excluded from donation.

Evaluation of a new fluorescent dye method to measure urinary albumin in lieu of urinary total protein

Urinary total protein (UTP) determinations are notoriously inaccurate, poorly reproducible, and difficult to interpret in early renal disease, causing many investigators to measure urinary albumin instead. In this study, we compare a new nonimmunologic fluorescent dye (AB-dye) for measuring albumin with the more expensive and cumbersome radioimmunoassay. We tested 207 urine specimens from patients with variable protein concentrations and divided the results into five arbitrary ranges (0 to 20, 21 to 50, 51 to 100, 101 to 200, and 201 to 400) for chi-square analysis. There was a high degree of correlation between the two methods (chi-square = 260. 8 with 16 degrees of freedom; P < 0.001). The correlation was also high when analyzed by linear regression (R = 0.86; F < 0.01). Based on our comparison of total protein and albumin concentration in the same urine samples, we hypothesized that patients with mild proteinuria may not necessarily have microalbuminuria. Urine samples with UTP between 150 and 400 microg/mL were tested for albumin by the AB-dye. Of 41 samples in this range, 18 (44%) had normal albumin levels. We conclude that measuring urinary albumin with the AB-dye is comparable in performance to radioimmunoassay and could replace UTP determinations, especially for patients with borderline elevations of UTP, many of whom do not have microalbuminuria.