Kidney Stones Linked to Higher Risk for Aortic Calcification

Pam Harrison

February 06, 2015

Patients who form calcium kidney stones are more likely to have higher abdominal aortic calcification (AAC) and lower vertebral bone mineral density (BMD) scores than those who do not develop kidney stones, a retrospective study suggests.

The study was published online January 29 in the Clinical Journal of the American Society of Nephrology.

Linda Shavit, MD, from the Royal Free Campus and Hospital, University College London Medical School, United Kingdom, and colleagues found that the prevalence of AAC was similar in patients who formed kidney stones (38%) compared with in non–stone forming control patients (35%).

However, 68%, of kidney stone formers (KSFs) had moderate to severe AAC scores compared with only 26% of non–stone forming controls (P < .001).

The average BMD, as assessed by computed tomography (CT), was also significantly lower, at 159 Hounsfield units in patients with a history of kidney stones compared with 194 Hounsfield units for those who did not (P < .001).

"[AAC] measured by CT scan is considered as a strong predictor of CV-related morbidity or death and was used in our study as a measure of [vascular calcification] burden in KSF and healthy control patients," the authors observe.

"[M]ultivariate analyses adjusted for all potential confounders confirmed that kidney stone disease is independently associated with advanced forms of [vascular calcification] compared with non-KSF."

Investigators carried out a retrospective matched case-control study that included KSFs attending the outpatient nephrology clinic of the Royal Free Hospital in London, United Kingdom, between 2011 and 2014.

The researchers drew age- and sex-matched non–stone formers from a list of potential living kidney donors from the same hospital. They investigated a total of 111 patients, 57 of whom were KSFs and 54 of whom were healthy controls. The mean age of both groups was 47 years.

AAC and vertebral BMD were assessed using CT imaging. AAC severity scores (presented as median [25th, 75th]) were significantly higher at in the KSF group compared with controls (0 [0, 43] vs 0 [0, 10]; P < .001).

The difference in AAC scores on multivariate models adjusted for age sex, high blood pressure, diabetes, smoking status, and estimated glomerular filtration rate was 3.78 units between KSF and non–stone formers (P < .001).

Similarly, the difference between the two groups on CT measures of BMD in the same multivariate model was −35.88 Hounsfield units (P < .001).

A higher AAC score also strongly correlated with lower BMD in both KSFs and non–stone formers (P < .001).

"Our study demonstrates that patients with calcium kidney stones suffer from significantly higher degrees of aortic calcification than age- and sex-matched non-stone formers," the investigators write, "suggesting that [vascular calcification] may be an underlying mechanism explaining reported associations between nephrolithiasis and [cardiovascular disease]."

Important Contribution

In an accompanying editorial, Eric Taylor, MD, from the Maine Medical Center, Portland, notes that the study represents "an important contribution" to the medical community's understanding of the potential relationships among calcium nephrolithiasis, lower BMD, and cardiovascular disease.

As Dr Taylor points out, AAC is a relevant study metric, being positively correlated with coronary artery calcification, an established predictor of incident nonfatal and fatal coronary heart disease.

In contrast, the study was not designed to elucidate mechanisms, and thus raises more questions than answers, Dr Taylor suggests.

"In the meantime, practicing nephrologists are left to wonder how the current state of research may affect the care of the patient with recurrent calcium stone disease," he writes.

It is still too early to incorporate a history of stone formation into current screening guidelines for either osteoporosis or CVD risk factors. "However, the savvy clinician is well aware that often the best therapies are not the newest or most complicated," Dr Taylor notes. "Perhaps it is always the right time to encourage a healthy diet with more fruits, vegetables, and whole grains and less red and processed meats and soda."

One coauthor is currently on secondment as a Chief Scientist with AstraZeneca. The other authors and Dr Taylor have disclosed no relevant financial relationships.

Clin J Am Soc Nephrol. Published online January 29, 2015. Abstract

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