Protein and albumin-to-creatinine ratios in random urines accurately predict 24 h protein and albumin loss in patients with kidney disease.
BACKGROUND
Random urine protein-to-creatinine (PCR) and albumin-to-creatinine (ACR) ratios have been proposed as alternatives to 24 h urine measurements to simplify sample collection and overcome errors. The aim of this study was to examine the ability of PCR and ACR to predict urinary 24 h protein and albumin loss, respectively, in patients with kidney disease, and determine the most appropriate time of collection.


METHODS
Eighty-three patients were recruited from a renal outpatient clinic. In a 24 h period, each collected an early-morning urine (EMU), second and third voids, and the remaining urine passed that day. PCR and ACR were determined in random urines and compared with the 24 h loss of protein and albumin, respectively.


RESULTS
For all patients, median (range) 24 h urine protein and albumin losses were 220 (30-15600) and 60 (<8-10,557) mg, respectively. Ratios derived from each of three random urines correlated well with 24 h protein or albumin loss (Spearman's r(s) > 0.87, P < 0.0001). Receiver operator characteristic (ROC) curve analysis showed PCR accurately predicted both an abnormal 24 h urine protein > or =150 mg/24 h (areas under curves [AUC] 0.90-0.92) and significant proteinuria above 300 mg/24 h (AUC between 0.97 and 1.00). ACR accurately predicted both an abnormal 24 h urine albumin > or =30 mg/24 h (AUC 0.98 to 0.99) and frank albuminuria at > or =300 mg/24 h or > or =700 mg/24 h (AUC between 0.99 and 1.00). EMU and random urines performed equally well in predicting proteinuria and albuminuria from PCR and ACR, respectively.


CONCLUSIONS
By careful choice of cut-offs, both PCR and ACR can be used in patients with kidney disease to rule in or rule out abnormal 24 h losses of protein and albumin. EMU and, importantly, random samples can be used as surrogates for 24 h urine collections.
Guy
Mark
M
Department of Clinical Biochemistry, Salford Royal NHS Foundation Trust, Hope Hospital, UK. mark.guy@srft.nhs.uk
Borzomato
Joanna K
JK
Newall
Ronald G
RG
Kalra
Philip A
PA
Price
Christopher P
CP
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000419:Albuminuria / Q000652:urine*; D019540:Area Under Curve; D002624:Chemistry, Clinical / Q000379:methods; D003404:Creatinine / Q000652:urine*; D005260:Female; D006801:Humans; D007674:Kidney Diseases / Q000652:urine*; D008297:Male; D008875:Middle Aged; D009398:Nephrology / Q000379:methods; D011507:Proteinuria / Q000652:urine*; D012372:ROC Curve; D015203:Reproducibility of Results; D013997:Time Factors; D016482:Urinalysis / Q000379:methods*
D003404:Creatinine