Researchers have developed equations for converting urinary protein-to-creatinine ratio (PCR) and urine dipstick protein categories to the gold standard albumin-to-creatinine ratio (ACR) for chronic kidney disease (CKD) screening, diagnosis, and risk prediction.
The Chronic Kidney Disease Prognosis Consortium developed equations to convert PCR and dipstick protein results to ACR using same-day measurements from 919,383 individuals in 12 research and 21 clinical cohorts. Mean age was 61 years; 50% of patients were female, 4.8% were Black, 56% had diabetes, and 72% had hypertension.
The investigators tested the estimating equations (both crude and adjusted) for CKD screening (ACR 30 mg/g or higher) and staging (stage A2: ACR of 30 to 299 mg/g; stage A3: ACR 300 mg/g or higher) using the 2012 Kidney Disease Improving Global Outcomes (KDIGO) guideline criteria. The team observed a consistent relationship between PCR and ACR across diverse cohorts at PCR levels of 50 mg/g and greater, but not below that level. The PCR conversion equations demonstrated moderate sensitivity (91%, 75%, and 87%) and high specificity (87%, 89%, and 98%) for screening and classification into stages A2 and A3, respectively, investigators reported in Annals of Internal Medicine. In contrast, the urine dipstick categories of trace to + and ++ had lower sensitivity (62%, 36%, and 78%) and high specificity (88%, 88%, and 98%) for the same parameters, respectively.
Furthermore, the investigators assessed patient risk for end-stage kidney disease. The estimated 2-year 4-variable kidney failure risk equation (KFRE) yielded similar results using measured and predicted ACR. The median c-statistic for the KFRE across cohorts was 0.879 for measured ACR versus 0.883 for predicted ACR. The crude model performed just as well as the adjusted model incorporating sex, hypertension, and diabetes.
The costs of measuring total protein are typically lower than those for measuring albumin.
According to Keiichi Sumida, MD, MPH, PhD, Girish Nadkarni, MD, MPH, and colleagues from the consortium, “our PCR conversion equations may have public health, clinical, and research implications from a practical and cost-effective perspective, facilitating the use of PCR as a screening, staging, and prognostic tool for CKD.”
“Although ACR measurement is not ubiquitous in all health care settings and is not available in all research settings, ACR-estimating equations, such as those reported in this study, may enhance both research and clinical care,” Tyrone G. Harrison, MD, and Brenda Hemmelgarn, MD, PhD, of the University of Calgary in Calgary, Alberta, Canada, commented in an editorial accompanying the study..
“In this setting, use of conversion equations from the inexpensive and widely available PCR or dipstick gives patients and clinicians in economically disparate locations access to such tools as the KFRE,” Dr Harrison and Dr Hemmelgarn wrote.
The link to the investigational PCR to ACR tool is ckdpcrisk.org/pcr2acr/
Sumida K, Nadkarni GN, Grams ME, et al; Chronic Kidney Disease Prognosis Consortium. Conversion of urine protein-creatinine ratio or urine dipstick protein to urine albumin–creatinine ratio for use in chronic kidney disease screening and prognosis: an individual participant-based meta-analysis [published online July 13, 2020]. Ann Intern Med. doi: 10.7326/M20-0529
Harrison TG, Hemmelgarn BR. From proteinuria to albuminuria: great expectations for kidney failure risk prediction [published online July 13, 2020]. Ann Intern Med. doi: 10.7326/M20-4211