Is morning urinary protein/creatinine ratio a reliable estimator of 24-hour proteinuria in patients with glomerulonephritis and different levels of renal function?
BACKGROUND
This cross-sectional study was conducted to determine whether a spot urine protein/creatinine ratio (UPr/UCr) provides accurate quantitation of 24-hr urinary protein excretion (24-hr Prot) in out-patients with primary glomerulonephritis (GN) and different renal function levels.


METHODS
Patients were classified into three groups according to creatinine (Cr) clearance (ml/min) and into five categories according to morning UPr/UCr. Correlation between 24-hr Prot and UPr/UCr was calculated according to the three renal function levels. The Bland and Altman method was used to assess agreement between 24-hr Prot and UPr/UCr. Agreement limits were obtained calculating the mean difference between 24-hr Prot and morning UPr/UCr +/- 2SD. Sensitivity and specificity were determined for different renal function levels and UPr/UCr cut-off values.


RESULTS
High correlation coefficients (r=0.91, 0.95 and 0.98) were observed in patients with normal, reduced and severely reduced renal function. Differences and variability between 24-hr Prot and UPr/UCr tended to increase with higher proteinuria levels, and this trend was observed for the three renal function levels. The best UPr/UCrcut-off values to detect abnormal or nephrotic proteinuria were, respectively, 0.3 and 2.6.


CONCLUSIONS
Correlation and agreement between UPr/UCr and 24-hr Prot was good for all renal function levels, but demonstrated more marked differences as urinary protein excretion increased. Morning UPr/UCr had good sensitivity and specificity for the diagnosis of 24-hr Prot, even in patients with reduced renal function.
Morales
José V
JV
Renal Division Hospital de Clinicas de Porto Alegre, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil. jvmmorales@terra.com.br
Weber
Raimar
R
Wagner
Mário B
MB
Barros
Elvino J G
EJ
D000293:Adolescent; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D003404:Creatinine / Q000652:urine*; D003430:Cross-Sectional Studies; D005260:Female; D005921:Glomerulonephritis / Q000652:urine*; D006801:Humans; D007677:Kidney Function Tests / Q000379:methods; D008297:Male; D008875:Middle Aged; D011507:Proteinuria / Q000652:urine*; D051437:Renal Insufficiency / Q000652:urine*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D003404:Creatinine