Urine Dipstick Protein Test Detects Silent Kidney Disease

From Medscape Medical News

Laurie Barclay, MD

August 4, 2011 — An inexpensive urine dipstick test can help screen for asymptomatic kidney disease, according to the results of a community-based, prospective cohort study reported online July 29 in the Journal of the American Society of Nephrology.
"We showed that routine inexpensive urine dipstick screening in a population with and without risk factors will allow primary clinicians to follow fewer patients with serial monitoring to identify those with rapid kidney function decline [RKFD] that will potentially benefit from earlier referral and therapeutic intervention," said lead author William F. Clark, MD, from the University of Western Ontario and London Health Sciences Centre in London, Canada, in a news release.
Although RKFD is associated with cardiovascular morbidity and mortality, serial evaluation of estimated glomerular filtration rate (eGFR) is not cost effective as screening in the general population. The investigators therefore assessed the predictive value of albuminuria and 3 thresholds of dipstick proteinuria to detect RKFD, defined as an annual decline from baseline eGFR of 5% or more.
The study cohort consisted of 2574 community-dwelling participants with follow-up for median duration of 7 years. Median change in eGFR was −0.78 mL/minute/1.73 m²/year, and RKFD developed in 8.5% of patients. Advancement to a new stage of chronic kidney disease (CKD) occurred in 64.7% of participants with RKFD and in 19.0% of those without RKFD.
Compared with albuminuria, a dipstick protein level of at least 1 g/L was a better predictor of RKFD.
If all participants (2.5% of the total cohort) who screened positive for a dipstick protein value of at least 1 g/L at baseline were monitored with serial eGFR, 1 of every 2.6 participants would have RKFD. Following this strategy for screening would correctly identify the 90.8% of patients who progressed to RFKD, would falsely label 1.5% as having RKFD, and would miss 7.7% of those in whom RKFD ultimately would develop.
"Among those with risk factors (cardiovascular disease, age >60, diabetes, or hypertension), the probability of identifying RKFD from serial eGFR measurements increased from 13 to 44% after incorporating dipstick protein (≥1g/L threshold)," the study authors write. "In summary, inexpensive screening with urine dipstick should allow primary care physicians to follow fewer patients with serial eGFR assessment but still identify those with rapid decline of kidney function."
Limitations of this study include possible selection bias.
"At the population level, this screening strategy may enable more appropriate targeting of resources," the study authors conclude. "However, future research must assess the effect and cost-effectiveness of different follow-up strategies in independent cohorts."


J Am Soc Nephrol. Published online July 29, 2011.