Despite their higher risk of chronic kidney disease, people with hypertension or diabetes usually are not given a simple test for protein in the urine to screen for this potentially deadly disorder, according to a study led by researchers at Johns Hopkins Bloomberg School of Public Health.

The researchers analyzed data on nearly four million hypertension and diabetes patients around the world, and found that only about 4% of the former and 35% of the latter had been screened for chronic kidney disease with a test for albuminuria, a standard measure of protein in the urine. This was despite the relatively high rates of chronic kidney disease that are generally found among hypertension and diabetes patients.

The study was published online August 9 in the journal Hypertension.

"These results highlight the need to widen albuminuria testing for early detection of chronic kidney diseases—especially now that we have new and more effective treatments that could benefit these patients," says study first author Jung-Im Shin, MD, an assistant professor in the Department of Epidemiology at the Bloomberg School.

"We're really missing a huge number of chronic kidney disease cases that should be detected and treated, and apart from all the other downsides of letting it go untreated, there is the fact that COVID-19 outcomes are often much worse for people with kidney disease," says study senior author Josef Coresh, MD, the George W. Comstock Professor in the Department of Epidemiology at the Bloomberg School.

According to the Centers for Disease Control and Prevention, about 37 million U.S. adults have chronic kidney disease, although the vast majority do not know it. Chronic kidney disease is easy to miss, especially in its early stages, because it typically features mild and nonspecific symptoms such as unexplained itching and swollen feet and ankles. It often progresses undiagnosed until late stages when kidney failure is unavoidable.

Testing for an abnormally high level of protein in the urine, a marker of kidney damage, is an accepted method for detecting possible chronic kidney disease. The clinically preferred test is called the ACR test, which measures the level in a urine sample of albumin, a common protein, corrected for the urine concentration as determined by the level of a molecule called creatinine.

Medical associations now recommend frequent ACR testing for people with diabetes, which often co-occurs with chronic kidney disease, and that patients with ACR levels of at least 30 mg/g—the threshold of albuminuria and a potential sign of early chronic kidney disease—be given medications to protect the kidneys. Many researchers believe that ACR testing in people with hypertension, another condition strongly linked to chronic kidney disease, would have significant benefits for similar reasons.

"There are new treatments for patients with albuminuria, including a class of drugs called SGLT2 inhibitors, which appear to be quite effective in protecting the kidneys as well as the cardiovascular system," Shin says. "Our findings suggest that albuminuria screening should be used much more often for detecting chronic kidney disease early, so that patients can benefit from earlier treatment."

To find out how often patients with diabetes or hypertension are given ACR urine tests to detect albuminuria, Shin, Coresh and their colleagues analyzed datasets including medical records for a total of 1,344,594 adults with diabetes and 2,334,461 adults who had hypertension but not diabetes. The datasets were assembled as part of the Chronic Kidney Disease Prognosis Consortium, a global research collaboration on chronic kidney disease that includes over 80 cohorts of patients across 40 countries. Coresh is a co-principal investigator for the consortium's Data Coordinating Center.

A key finding was that only 4.1% of the hypertension patients and 35.1% of the diabetes patients had had an ACR test during a two-year time window starting with their inclusion in a dataset. This was despite the fact that in these groups, those who were given ACR tests had relatively high rates of albuminuria defined as ACR ≥ 30 mg/g: 32.1% for the diabetes patients, and 21.8% for the hypertension patients. Additionally, in both groups more than 20% of those with ACR < 30 mg/g in the initial time window converted to ACR ≥ 30 mg/g in the ensuing five years.

The analysis further showed that whether a patient received an ACR test or not essentially had nothing to do with his or her predicted risk of ACR ≥ 30 mg/g.

"People who were tested were not those at highest risk—they were just a random subset," Coresh says. "So we estimate that the number of patients with undetected ACR ≥30 mg/g was far greater than the number of detected cases—almost 20 times greater among the hypertension patients."

The study also included the development of a risk model—one of many now available for physicians who are considering the possibility of chronic kidney disease in a patient—that predicts the development of ACR ≥ 30 mg/g within a few years. Prominent risk factors in the model included older age, male sex, history of heart failure, and a lower measure of kidney filtration rate.