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Conversion of Urine Protein to Urine Albumin–Creatinine Ratio for Chronic Kidney Disease
Quick Takes
- Urine protein–creatinine ratio (PCR) and dipstick urine protein can be useful for identifying patients with albuminuria, a defining feature of chronic kidney disease.
- The relationship between urine PCR or dipstick protein and urine albumin-creatinine ratio (ACR) is most reliable with greater degrees of proteinuria.
- A tool for converting PCR or dipstick values to ACR is available at: http://www.ckdpcrisk.org/pcr2acr/.
Study Questions:
Can urine protein–creatinine ratio (PCR) and urine dipstick protein serve as substitutes for urine albumin–creatinine ratio (ACR) in assessment of chronic kidney disease (CKD)?
Methods:
Cohorts of 200 or more participants with ACR and PCR/dipstick protein obtained on the same day were identified from the CKD Prognosis Consortium. Methods of collecting urine to assess ACR, PCR, and urine dipstick protein included morning spot urine, random spot urine, and 24-hour urine. Estimated glomerular filtration rate (eGFR) was calculated based on serum creatinine with the CKD Epidemiology Collaboration equation. Relationships between ACR and PCR were modeled with multivariable-adjusted linear regression models.
Results:
The study included 919,383 participants in 33 cohorts, with data collected from 1982-2019. Mean age was 61 years; 50% of participants were female, 4.8% were black, 56% had diabetes, and 72% had hypertension. Median ACR was 14 mg/g, and mean eGFR was 80 ± 25 ml/min/1.73 m2.
For PCR values >50 mg/g, the relationship between PCR and ACR was nearly linear on a logarithmic scale, while the association was inconsistent for PCR <50 mg/g. Urine dipstick protein categories (i.e., trace, +, ++, and greater than ++) and ACR exhibited a graded relationship. Thresholds of the PCR levels corresponding to predicted ACRs of 30 mg/g (corresponding to CKD stage A2) and 300 mg/g (corresponding to CKD stage A3) were 142 mg/g and 660 mg/g, respectively. Meta-analyzed sensitivity of the PCR-based equation for detecting ACR of 30 mg/g or above was 91.2%, specificity 86.5%, positive predictive value 91.1%, and negative predictive value 84.5%. Dipstick values of trace to + had low sensitivity for CKD stage A2 (62.0%), while dipstick values of ++ had meta-analyzed sensitivity and specificity of 77.6% and 97.5%, respectively, for CKD stage A3.
A tool for converting PCR or dipstick values to ACR, based on the above results, is available at: http://www.ckdpcrisk.org/pcr2acr/.
Conclusions:
Urine PCR and dipstick urine protein can be useful for identifying patients with albuminuria. However, the relationship between urine PCR or dipstick protein and urine ACR is unreliable when low-grade proteinuria is present.
Perspective:
Previous work has demonstrated that albuminuria and eGFR impairment are multiplicatively associated with all-cause and cardiovascular mortality (van der Velde M, et al., Kidney Int 2011;79:1342-52, doi: 10.1038/ki.2010.536). However, screening for albuminuria remains limited in clinical practice, especially in nondiabetic patients. The idea of using urine PCR or dipstick protein as a poor-man’s ACR seems appealingly convenient, but the absence of urine protein on these tests does not definitively exclude albuminuria. The results of the present study should be validated in prospective cohorts.
Clinical Topics: Diabetes and Cardiometabolic Disease, Prevention, Hypertension
Keywords: Albumins, Albuminuria, Creatinine, Diabetes Mellitus, Hypertension, Kidney Diseases, Kidney Glomerulus, Metabolic Syndrome, Polymerase Chain Reaction, Primary Prevention, Proteinuria, Renal Insufficiency, Chronic, Urine Specimen Collection
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