Hypertension and diabetes have reached epidemic proportions in the United States. Most of the burden of caring for affected patients falls squarely on the shoulders of primary care physicians. Since patients with these conditions are at high risk for cardiovascular and renal disease, the question is whether there is a quick, inexpensive, and reliable test to screen patients who have hypertension (with or without diabetes) and those who have cardiovascular diseases who are at increased risk for renal deterioration? Urine tests, for instance, are a quick, inexpensive, and reliable way to identify microalbuminuria, albuminuria, and proteinuria.
What works optimally and efficiently in the primary care setting?
To find out, Clark and colleagues1 followed 2574 persons for 7 years, assessing proteinuria (not albuminuria) by simple urine dipstick as well as spot urine albumin:creatinine ratio (ACR). The team also measured glomerular filtration rate (GFR) (7 readings during the study) and estimated the rate of kidney function deterioration in an effort to predict rapid kidney function decline (RKFD-defined as >5% decline/year).
Not surprisingly, people with RKFD were older and had a higher incidence of elevated blood pressure, diabetes (family and personal occurrence), and cardiovascular disease. Dipstick proteinuria (estimate >1 g/L) was a stronger predictor of RKFD than the spot urine albumin/creatinine ratio. Although simple, inexpensive, and quick, the screening strategy correctly identified a progressive kidney problem in 90.8% of patients. The incidences of incorrect and missed diagnosis of RKFD were 1.5% and 7.7%, respectively.
Applying these results to clinical practice, here is the take-home message: if your population includes patients older than 60 years who have hypertension, diabetes, or cardiovascular disease, adding dipstick urine protein positivity to your screening increases the probability of discovering RKFD from|13% to 44%. This is based on a sample estimating smaller (>1 g/L) protein excretions. If the dipstick is positive for a greater (>3 g/L) amount of protein, the likelihood of RKFD increases by 7.8 times. Of course, we should not overlook albuminuria either. Although not quite as simple or quick to measure as an office dipstick test, this study found that a high albumin values conferred a 53% greater risk for RKFD.
The findings of this study were so straightforward that it boggles the mind. In an era of expensive, invasive testing, just “dipsticking” a urine sample in an ambulatory setting in a high-risk population gives primary care physicians important information about their renal prognosis.
In this study, 90% of the participants were white. Hopefully, further study will corroborate these findings in ethnically dissimilar populations as well.