Calculated insulin resistance correlates with stone-forming urinary metabolic changes and greater stone burden in high-risk stone patients.

AIMS: Metabolic syndrome and diabetes are associated with nephrolithiasis. Proposed mechanisms of lithogenesis include insulin resistance causing low urine pH and hyperinsulinemia leading to hypercalciuria. Herein, we sought to determine whether insulin resistance was associated with differences in stone burden and lithogenic changes on 24-hour urine samples. MATERIALS AND METHODS: All patients that underwent comprehensive metabolic workup including 24-hour urine samples and fasting insulin levels were included. Insulin resistance was defined as a homeostasis model assessment of insulin resistance value > 5 (HOMA-IR = (glucose×insulin)/405). Patients on active metabolic therapy were excluded or the 24-hour urine sample predating treatment was utilized for analysis. Stone burden was determined by totaling the maximal diameter of all stones noted on CT. RESULTS: 18 of 30 patients (60.0%) had HOMA-IR > 5. Among patients with calculated insulin resistance, stone burden was greater (17.6 mm vs. 6.3 mm, p = 0.002) and 24-hour urine samples revealed higher urine calcium (293 mg/d vs. 159 mg/d, p = 0.02) and lower urine pH and citrate (454 mg/d vs. 639 mg/d, p = 0.04 and 5.83 vs. 6.33, p = 0.04, respectively). CONCLUSIONS: Previous studies have demonstrated a correlation between metabolic syndrome, diabetes, and nephrolithiasis. This report demonstrates a quantitative increase in stone burden among patients with calculated insulin resistance. The pathway for this greater stone burden may be related to the urinary metabolic changes noted among patients with insulin resistance. In the future, targeting reduction of fasting insulin levels may represent a key element of stone disease prevention.

Bone disease and pathologic fractures in a patient with tenofovir-induced Fanconi syndrome.

We report the case of an HIV-positive patient with preexisting bone disease who developed tenofovir-induced Fanconi syndrome and subsequently sustained pathologic fractures. We suggest that tenofovir treatment may have contributed to the patient's pathologic fractures through its effects on phosphorus balance and vitamin D metabolism. This case highlights the importance of monitoring not only for renal impairment but also for bone disease in patients receiving tenofovir treatment, especially given the high prevalence of osteopenia and osteoporosis in HIV-positive patients.

The growing prevalence of kidney stones and opportunities for prevention.

The prevalence of kidney stones is climbing in the United States. Several investigators have demonstrated an association between metabolic syndrome and kidney stones and some have proposed a causal link. Risk factors for nephrolithiasis can be identified with a 24-hour urine collection and preventive measures can be customized to meet the needs of individual patients. Dietary and pharmacologic interventions are available to address urinary risk factors such as inadequate urine volume, hypercalcuria, hyperoxaluria, hyperuricosuria and hypocitraturia. Given that morbidity and healthcare costs associated with nephrolithiasis are on the rise, deterring stone formation is increasingly important. Multidisciplinary clinics that foster collaboration between urologists, nephrologists and dieticians offer patients effective prevention and treatment strategies.

Epidemiology and outcomes of acute renal failure in hospitalized patients: a national survey.

The aim of this study was to provide a broad characterization of the epidemiology of acute renal failure (ARF) in the United States using national administrative data and describe its impact on hospital length of stay (LOS), patient disposition, and adverse outcomes. Using the 2001 National Hospital Discharge Survey, a nationally representative sample of discharges from nonfederal acute care hospitals in the United States, new cases of ARF were obtained from hospital discharge records coded according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). Multivariate regression analyses were used to explore the relation of ARF to hospital LOS and mortality as well as discharge disposition. Review of discharge data on a projected total of 29,039,599 hospitalizations identified 558,032 cases of ARF, with a frequency of 19.2 per 1000 hospitalizations. ARF was more commonly coded for in older patients; men; black individuals; and the setting of chronic kidney disease, congestive heart failure, chronic lung disease, sepsis, and cardiac surgery. ARF was associated with an adjusted prolongation of hospital LOS by 2 d (P < 0.001) and an adjusted odds ratio of 4.1 for hospital mortality and of 2.0 for discharge to short- or long-term care facilities. In a US representative sample of hospitalized patients, the presence of an ICD-9-CM code for ARF in discharge records is associated with prolonged LOS, increased mortality, and, among survivors, a greater requirement for posthospitalization care. These findings suggest that in the United States, ARF is associated with increased in-hospital and post-hospitalization resource utilization.