Albumin-Creatinine Ratio Better for Chronic Kidney Disease Screening

Keiichi Sumida, MD, MPH, PhD

Currently, measuring albuminuria is the preferred method for defining and staging chronic kidney disease (CKD). However, measuring total urine protein or dipstick protein can be an alternative to albuminuria.

A team, led by Keiichi Sumida, MD, MPH, PhD, Division of Nephrology, Department of Medicine, University of Tennessee Health Science Center, developed equations for converting urine protein-creatinine ratio (PCR) and dipstick protein to urine albumin-creatinine ratio (ACR) and tested their diagnostic accuracy in chronic kidney disease screening and staging.

In the individual-based meta-analysis, the investigators examined data from 919,383 adults with same-day measures of ACR and PCR or dipstick protein from 12 research and 21 clinical cohorts.

The team developed equations to convert urine PCR and dipstick protein to ACR. They tested the equations for purposes of chronic kidney disease screening (ACR ≥30 mg/g) and staging (stage A2: ACR of 30 to 299 mg/g; stage A3: ACR ≥300 mg/g).

The median ACR was 14 mg/g (25th to 75th percentile of cohorts, 5 to 25 mg/g).

The investigators found the link between PCR and ACR was inconsistent for PCR values less than 50 mg/g. For higher PCR values, the PCR conversion equations showed moderate sensitivity (91%, 75%, and 87%), as well as for specificity (87%, 89%m and 98%) for screening (ACR >30 mg/g) and classification into stages A2 and A3, respectively.

Urine dipstick categories of trace or greater, trace to +, and ++ for screening for ACR values greater than 30 mg/g and classification into stages A2 and A3, respectively, had moderate sensitivity (62%, 36%, and 78%) and high specificity (88%, 88%, and 98%).

The investigators also found for individual risk prediction, the estimated two-year four-variable kidney failure risk equation using predicted ACR from PCR had discrimination similar to that of using observed ACR.

“Urine ACR is the preferred measure of albuminuria; however, if ACR is not available, predicted ACR from PCR or urine dipstick protein may help in CKD screening, staging, and prognosis,” the authors wrote.

Earlier this year, researchers found proteinuria levels following an acute kidney injury (AKI) could help predict the future risk of the loss of renal function.

A team from several different institutions, led by Chi-yuan Hsu, MD, Division of Nephrology, University of California School of Medicine, San Francisco, found that more widespread quantification of proteinuria after a hospitalized acute kidney injury should be considered to better evaluate the risk of future kidney disease progression.

Higher post-AKI urine ACR level was associated with increased risk of kidney disease progression (HR, 1.53 for each doubling; 95% CI, 1.45-1.62), and urine ACR measurement was a strong discriminator for future kidney disease progression (C statistic, .82).

The investigators also found the performance of urine ACR was stronger for patients who had AKI than in those who had not (C statistic, .70).

The study, “Conversion of Urine Protein—Creatinine Ratio or Urine Dipstick Protein to Urine Albumin–Creatinine Ratio for Use in Chronic Kidney Disease Screening and Prognosis,” was published online in the Annals of Internal Medicine.