Few Patients with Abnormal Urine Protein Dipstick Results Get Follow-Up Albuminuria Testing

Yunwen Xu, PhD

Credit: Johns Hopkins

Findings from a recent study are calling attention to missed opportunities for heart and kidney disease detection with follow-up albuminuria testing after abnormal urine protein dipstick results.¹

Of more than 1 million patients tested across 33 US health systems, 13% had abnormal protein levels, and just 6.7% of patients with abnormal results had further testing for albuminuria within 1 year as recommended by clinical guidelines.¹

Albuminuria is a sign of kidney disease and indicates an excess of albumin excretion in the urine (>30 mg/L). While healthy kidneys do not allow albumin to pass from the blood into the urine, damaged kidneys let some albumin pass. It is also an important risk factor for cardiovascular disease and death, underscoring the importance of accurate albuminuria quantification and routine albuminuria testing.²

“Although urine ACR is the most accurate method for quantifying albuminuria, dipstick urinalysis tests are inexpensive and are often used as an initial screening test, with guidelines recommending follow-up ACR testing if the protein dipstick test result is abnormal. Whether this approach is followed in real-world settings is unknown,” Yunwen Xu, PhD, of the department of epidemiology at Johns Hopkins Bloomberg School of Public Health, and colleagues wrote.¹

To assess follow-up albuminuria quantification after an initial abnormal result on a protein dipstick test, investigators leveraged deidentified electronic health record data from the Optum Labs Data Warehouse for nonpregnant adults with ≥ 1 outpatient encounter and assessment of serum creatinine who had protein dipstick testing in 2021. Patients with known albuminuria determined by albumin–creatinine ratio (ACR) or equivalent protein-creatinine ratio (PCR) and those with prior ACR or PCR testing within 6 months before the index date were excluded.¹

Investigators defined an abnormal result as 1+ or greater protein in the absence of positive results for leukocyte esterase or nitrites. The primary outcome was subsequent quantitative albuminuria testing with ACR or PCR, estimated over 1 year using Kaplan-Meier methods with censoring at the last encounter, death, or end of the 1-year study period. Investigators also estimated the proportion of individuals with an abnormal result on a protein dipstick test who were subsequently confirmed to have albuminuria, defined as an ACR or equivalent PCR value of ≥ 30 mg/g at any time during 1-year follow-up.¹

Investigators identified 1,042,740 patients with urine dipstick testing in 33 US health systems. Among the cohort, the mean age was 58 (Standard deviation, 17) years, 60% of patients were female, and 77% were White.¹

In total, 138,306 (13%) patients had an abnormal protein dipstick test result. Investigators noted the cumulative 1-year incidence of follow-up albuminuria testing was 6.7% among participants with abnormal dipstick test results at baseline, compared with 4.0% among those with normal results at baseline.¹

They pointed out follow-up testing rates were slightly greater with increased values of the initial abnormal test: 6.3%, 7.3%, and 8.0% for 1+, 2+, and 3+ or greater protein, respectively (P for trend <.001). Additionally, follow-up testing was more common among participants with diabetes (16.6%) than among those without diabetes (3.8%), and most follow-up albuminuria testing was done with ACR (86%).¹

Among the 7967 participants with initial abnormal results on a dipstick protein test who had follow-up albuminuria quantification testing, the proportion who had a positive result confirming albuminuria was 43.3% (95% CI, 42.2% to 44.4%). Investigators noted this percentage increased with greater baseline protein levels, from 36.3% (CI, 35.0% to 37.6%) for 1+ protein to 53.0% (CI, 50.9% to 55.1%) for 2+ protein and 64.9% (CI, 61.4% to 68.5%) for ≥ 3+ protein.¹

Additional analysis stratified by the presence of diabetes showed similar percentages with confirmatory albuminuria for participants with and without diabetes. Results were also consistent when 2 results confirming albuminuria were required.¹

Investigators acknowledged their inability to determine reasons for ordering urinalyses or whether providers were aware of the abnormal results as major limitations to these findings.¹

“There is a crucial need for follow-up with ACR testing, which offers greater accuracy and is essential for determining whether to initiate cardiorenal protective therapies,” investigators concluded.¹ “Improved education on the necessity of follow-up albuminuria quantification and the implementation of guideline-recommended ACR testing would benefit many patients through earlier detection and treatment of albuminuric CKD.”

References

1. ^{Xu Y, Shin JI, Wallace A, et al. Shortfalls in Follow-up Albuminuria Quantification After an Abnormal Result on a Urine Protein Dipstick Test. Ann Intern Med. doi:10.7326/ANNALS-24-00549}
2. ^{National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Albuminuria: Albumin in the Urine. Health Information. October 2016. Accessed October 1, 2024. https://www.niddk.nih.gov/health-information/kidney-disease/chronic-kidney-disease-ckd/tests-diagnosis/albuminuria-albumin-urine}