The key to a man’s heart might be through his stomach, but how healthy that heart is might actually depend on an organ slightly further down.

That’s the verdict reached by a study published this morning in the Lancet Diabetes and Endocrinology. In an extensive review of 24 studies that altogether involved over 674,000 participants, the study authors found that widely used measures of kidney function proved to be just as good as or better at predicting later cardiovascular disease than commonly used tests of cholesterol and blood pressure.

The authors keyed in on measurements of the waste product creatinine in the blood and the protein albumin in the urine, called albuminuria. Both are commonly used to signal lagging kidney function — healthy kidneys filter out creatinine and albumin before they reach the blood and urine respectively. The former is then indirectly used to determine the estimated glomerular filtration rate (eGFR) of the kidney, with higher levels showing better kidney health.

The authors tabulated these test results, alongside cholesterol and systolic blood pressure readings, to see how well each could independently predict later cardiovascular damage among the participants, after controlling for other factors. Participants’ eGFR levels held up well as a risk factor, particularly for later heart disease and stroke, but high albuminuria levels proved to be an even better tool than cholesterol, blood pressure, and smoking history for determining risk of heart failure and death from a heart attack or stroke. The authors also found those with chronic kidney disease were twice as likely to eventually develop accompanying heart disease than those with healthy kidneys.

"Cholesterol levels and blood pressure tests are good indicators of cardiovascular risk, but they are not perfect. This study tells us we could do even better with information that often times we are already collecting," said lead author Dr. Kunihiro Matsushita, of the Johns Hopkins Bloomberg School of Public Health, in a press release. Though these kidney tests are already often recommended for those with conditions like diabetes and hypertension, Matsushita said there are specific populations who could greatly benefit from them, the study finding that the link between kidney and heart health was especially profound among blacks.

That link isn’t entirely understood as of yet, though Matsushita believes it may have something to do with the fluid overload created by poorly working kidneys, as well as kidney disease patients not being given certain medications known to help with heart disease. Regardless, the authors are hopeful their findings will push physicians to expand their proverbial bag. "If health care providers have data on kidney damage and kidney function — which they often do — they should be using those data to better understand a patient's risk of cardiovascular disease," Matsushita said.

Source: Matsushita K, Coresh J, Sang Y, Chalmers J, et al. Estimated Glomerular Filtration Rate and Albuminuria for Prediction of Cardiovascular Outcomes: A Collaborative Meta-Analysis. Lancet Diabetes and Endocrinology. 2015.