Kidney stones are found in 11% of the population and are more than twice as common in men as in women.1 Patients with underlying metabolic conditions (ie, obesity, diabetes, hypertension, hyperuricemia, hypercholesterolemia, hypertension, chronic kidney disease) are much more likely than others to have kidney stones. This is also a population at increased risk for cardiac disease. So if a patient has both kidney stones and heart disease, is kidney stone disease a cause or effect of heart disease? Or are the causes of heart disease also the causes of kidney stones?
For many years, professionals thought the population affected by kidney stones was also the group with risk factors for heart disease—that the metabolic conditions were found in both groups, but that the stones were not meaningful: The finding of kidney stones in the cardiac patient was an incidental, and slightly interesting, finding. Yet a study published recently in the American Journal of Kidney Disease has turned this concept on its head.2 Liu and associates have done a meta-analysis of studies involving more than 3.5 million patients to explain exactly how kidney stones are related to cardiac disease.
In 1973, Westlund reported that patients who had kidney stones were just as likely to have had a myocardial infarction (MI).3 He was unable to identify an increased risk for MI in stone formers in his all-male cohort. In 1976, Elmfeldt and colleagues reported twice as many MIs in study subjects with kidney stones as in patients without stones.4 However, that same year, Ljunghall and Hedstrand were unable to find a correlation between kidney stones and heart disease in middle-aged men.5 Recently, Rule et al, using a 10,800-member study cohort of Minnesota residents, did show a 31% increased incidence of MI in patients with kidney stones.6
Liu and his group decided to try to answer this question once and for all. Using a graded system that examined studies of kidney stone patients who also showed signs of cardiac disease, they performed a meta-analysis comparing 50,000 patients with kidney stones and more than 3.5 million controls (patients without kidney stones). Controlling for the standard risk factors within this group (eg, age, gender, BMI, medication use, diabetes, smoking, alcohol use), the investigators identified kidney stones as a separate identifiable risk factor for cardiac disease.
In fact, Liu’s study team was able to quantify exactly how much greater a risk for cardiac disease exists in a kidney stone patient.2 Using a multivariate outcomes data plot and defining cardiac disease using hard endpoints (fatal or nonfatal MI or coronary revascularization), the researchers found a 19% increase in cardiac disease among the kidney stone patients.7 When the endpoint used was cerebrovascular accident (CVA), patients with kidney stones had a 40% higher rate of stroke.
However, the real shock came when Liu and colleagues looked at the risk factors by gender. Quite simply, women with kidney stones had a higher rate of cardiac disease and stroke than men. In totality, the increased risk for cardiac disease and stroke for a male stone patient was not statistically significant. But in female stone patients, a 40% higher rate of stroke and a 31% higher rate of cardiac disease was discovered. This explains the huge disparity in previous studies. The increased risk for cardiac disease in the kidney stone patient is borne solely by the females of the population!2
Thus, we need to aggressively evaluate and treat our female patients for heart disease when they present with kidney stones. Just as the woman’s symptoms of MI are not “classic,” and one needs to consider gender when evaluating for MI, so do we need to consider gender in the kidney stone patient.8
Next time your patient is a woman with a kidney stone, remember to raise cardiac issues with her. The MI you prevent may be in my mother or my sister.
REFERENCES
1. Wells CG, Chandrashekar KB, Jyothirmayi GN, et al. Kidney stones: current diagnosis and management. Clinician Reviews. 2012;22(2):31-37.
2. Liu Y, Li S, Zeng Z, et al. Kidney stones and cardiovascular risk: a meta-analysis of cohort studies. Am J Kidney Dis. 2014;64(3):402-410.
3. Westlund K. Urolithiasis and coronary heart disease: a note on association. Am J Epidemiol. 1973;97(3):167-172.
4. Elmfeldt D, Vedin A, Wilhelmsson C, et al. Morbidity in representative male survivors of myocardial infarction compared to representative population samples. J Chronic Dis. 1976;29(4):221-231.
5. Ljunghall S, Hedstrand H. Renal stones and coronary heart disease. Acta Med Scand. 1976;199(6):481-485.
6. Rule AD, Roger VL, Melton LJ 3rd, et al. Kidney stones associate with increased risk for myocardial infarction. J Am Soc Nephrol. 2010;21(10):1641-1644.