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Abstract: SA-PO1111

Comparison of Different Methods of Urinary Protein Excretion Measurement–Is the King Really Dead?

Session Information

Category: Pathology and Lab Medicine

  • 1502 Pathology and Lab Medicine: Clinical

Authors

  • Rydzewska-Rosolowska, Alicja, Medical University of Bialystok, BIALYSTOK, Poland
  • Kakareko, Katarzyna, Medical University of Bialystok, BIALYSTOK, Poland
  • Hryszko, Tomasz, Medical University of Bialystok, Bialystok, Poland
  • Brzosko, Szymon, DaVita Poland, Bialystok, Poland
  • Naumnik, Beata, Medical University of Bialystok, BIALYSTOK, Poland
Background

Assessing proteinuria is one of the most important diagnostic tests for a clinical nephrologist. When treating patients, it is often indispensable to accurately quantify the amount of protein lost, hence cumbersome timed urine collections (the gold standard or “king” of methods– 24h protein excretion rate- PER) are often replaced by spot urinary protein to creatinine ratio (PCR). The aim of the study was to determine whether the latter can reliably compare to the gold standard and whether “timing” of a spot urine sample is essential (as there is a diurnal and postural effect on protein excretion).

Methods

143 adult patients hospitalized in the I Department of Nephrology with proteinuria (both primary and secondary glomerular diseases) were examined (a total of 187 cases). Subjects with an active infection or tumors of the urinary tract were excluded. Each patient was instructed how to perform a 24-hour urine collection and on the same day three consecutive urine samples were also collected (starting with the first morning void). Concentration of protein and creatinine in spot urine samples and the timed urine collection were measured.

Results

PCR from all three spot samples moderately correlated with 24h PER (0.76, 0.79 and 0.82 respectively). Log transformation of examined variables slightly improved observed association (0.80, 0.84 and 0.86). The sensitivity and specificity for proteinuria above 1.0 g/day were 0.79 and 0.73 for sample 1, 0.82 and 0.68 for sample 2 and 0.82 and 0.67 for sample 3. For nephrotic proteinuria it was respectively 0.62 and 0.94, 0.62 and 0.93, 0.66 and 0.92.
Sex, age, weight and serum albumin concentration were significantly associated with 24h PER and were used for development of prediction equation yielding adjusted R2of 0.78, 0.83 and 0.86. Bland-Altman analysis revealed an increasing difference between 24h PER and PCR with increasing proteinuria irrespectively of sampling time.

Conclusion

In patients with primary and secondary glomerular diseases spot urine protein to creatinine ratio only modestly correlates with daily proteinuria whether it’s morning or random urine sample. It seems, while searching for new markers, nephrologists can just say: “long live the king”.