Evaluation and Management of Nephrolithiasis in the Aging Population With Chronic Kidney Disease

Anna L Zisman; Fredric L Coe; Elaine M Worcester

Disclosures

Aging Health. 2011;7(3):423-433. 

In This Article

Evaluation of the Geriatric Stone Former or the Geriatric Stone Former With CKD

The risk factors for nephrolithiasis in the elderly are similar to those of the general population, and the initial evaluation is the same as for any stone former.[21] Specifically, the key points of the evaluation include a thorough personal medical and lifestyle history, family history of stone disease or osteoporosis, dietary history, and review of radiologic studies to appreciate the stone burden, time course of the disease (if sequential studies are available) and potential renal anatomic abnormalities. As with a stone former of any age, at least two complete 24-h urine collections are required for a thorough evaluation of metabolic risk factors, with measurements of total 24-h excretions of creatinine, sodium, citrate, calcium, oxalate, phosphorus, potassium, magnesium, sulfate, ammonium and uric acid, along with measurement of 24-h urine volume and pH.[22] Whether screening the initial urine collection for cystinuria is prudent and cost effective in the first-time geriatric stone former with an unknown stone type is debatable, but recent data suggest that late presentation with cystinuria is not uncommon.[23] A serum chemistry panel with a creatinine and uric acid level should be drawn with each urine collection, with special emphasis on evaluation of serum calcium and bicarbonate levels. The calcium values are important in ruling out primary hyperparathyroidism, as well as in the evaluation of bone and mineral health in CKD. If serum calcium is elevated, parathyroid hormone (PTH) levels should be obtained. Serum bicarbonate is crucial as it can point to a renal tubular acidosis as an etiology of stone disease, while also being a key parameter in the management of CKD.

The 24-h urine collections should be analyzed in a specialized laboratory experienced in kidney stone risk evaluation and calculation of supersaturations for various stone types, such as calcium oxalate, calcium phosphate and uric acid. Supersaturation is the ratio of the activity product of a given stone salt (such as calcium phosphate) in a given urine to its known solubility product. A ratio of >1 suggests that the urine is supersaturated with regard to that stone salt, increasing the likelihood of crystallization. Calculation of supersaturations in the urine is important for determination of future risk for lithogenesis, and durable long-term stone-free survival has been demonstrated by targeting lower supersaturations as a goal of treatment.[24] It is important to mention that checking any individual metabolite is unlikely to be helpful, as the risk of stone formation is determined by the interaction among the metabolites and influenced by volume and pH. Furthermore, spot urine specimens are also unlikely to be helpful, as our group has previously demonstrated that urinary excretions of a number of metabolites vary with meals.[25]

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