Faculty Bibliography

PURPOSE: In general high urine supersaturation with respect to calcium oxalate, calcium phosphate or uric acid is associated with that phase in stones. We explore the exceptions when supersaturation is high and a corresponding solid phase is absent (type 1), and when the solid phase is present but supersaturation is absent or low (type 2). MATERIALS AND METHODS: Urine supersaturation values for calcium oxalate, calcium phosphate and uric acid, and other accepted stone risk factors were measured in 538 patients at a research clinic and 178 at stone prevention sites in a network served by a single laboratory. RESULTS: Of the patients 14% lacked high supersaturation for the main stone constituent (type 2 structural divergence) because of high urine volume and low calcium excretion, perhaps from changes in diet and fluid intake prompted by stones. Higher calcium excretion and low urine volume caused type 1 divergences, which posed no clinical concern. CONCLUSIONS: Type 1 divergence appears to represent a condition of low urine volume which raises supersaturation in general. Almost all of these patients are calcium oxalate stone formers with the expected high supersaturation with calcium oxalate as well as high uric acid and calcium phosphate supersaturations without either phase in stones. Type 2 divergence appears to represent an increase in urine volume and decrease in urine calcium excretion between stone formation and urine testing

The first episode of nephrolithiasis provides an opportunity to advise patients about measures for preventing future stones. Low fluid intake and excessive intake of protein, salt and oxalate are important modifiable risk factors for kidney stones. Calcium restriction is not useful and may potentiate osteoporosis. Diseases such as hyperparathyroidism, sarcoidosis and renal tubular acidosis should be considered in patients with nephrolithiasis. A 24-hour urine collection with measurement of the important analytes is usually reserved for use in patients with recurrent stone formation. In these patients, the major urinary risk factors include hypercalciuria, hyperoxaluria, hypocitraturia and hyperuricosuria. Effective preventive and treatment measures include thiazide therapy to lower the urinary calcium level, citrate supplementation to increase the urinary citrate level and, sometimes, allopurinol therapy to lower uric acid excretion. Uric acid stones are most often treated with citrate supplementation. Data now support the cost-effectiveness of evaluation and treatment of patients with recurrent stones

The pathophysiology of stone disorder in older adults, as compared to their younger counterparts, has not been thoroughly investigated. This article examines the differences in serum and urine chemistries between groups that are younger and older than 60 years of age. The principal finding is that stone formation occurs at lower urinary supersaturations in older patients, suggesting that other unexplored factors are significant contributors. The authors then review the possible effect of age on the morbidity of stone disease and the implications of stone disease for the development and management of osteoporosis

PURPOSE: We determined whether a network of 7 comprehensive kidney stone treatment centers supported by specialized stone management software and laboratory resources could achieve reductions in urine supersaturation comparable to those in a single research clinic devoted to metabolic stone prevention. MATERIALS AND METHODS: Supersaturation values for calcium oxalate, calcium phosphate and uric acid in 24-hour urine samples were calculated from a set of kidney stone risk factor measurements made at a central laboratory site for the network and research laboratory for the clinic. Individual results and group outcomes were presented to each center in time sequential table graphics. The decrease in supersaturation with treatment was compared in the network and clinic using analysis of variance. RESULTS: Supersaturation was effectively reduced in the network and clinic, and the reduction was proportional to the initial supersaturation value and increase in urine volume. The clinic achieved a greater supersaturation reduction, higher fraction of patient followup and greater increase in urine volume but the treatment effects in the network were, nevertheless, substantial and significant. CONCLUSIONS: Given proper software and laboratory support, a network of treatment centers can rival but not quite match results in a dedicated metabolic stone research and prevention clinic. Therefore, large scale stone prevention in a network system appears feasible and effective

BACKGROUND: Several studies have suggested that if recombinant human erythropoietin (epoetin) is administered subcutaneously rather than intravenously, a lower dose may be sufficient to maintain the hematocrit at a given level. METHODS: In a randomized, unblinded trial conducted at 24 hemodialysis units at Veterans Affairs medical centers, we assigned 208 patients who were receiving long-term hemodialysis and epoetin therapy to treatment with either subcutaneous or intravenous epoetin. The dose was initially reduced until the hematocrit was below 30 percent and then was gradually increased to a level that would maintain the hematocrit in the range of 30 to 33 percent for 26 weeks. We compared the average doses in the 26-week maintenance phase and the discomfort associated with the two routes of administration. RESULTS: For the 107 patients treated by the subcutaneous route, the average weekly dose of epoetin during the maintenance phase was 32 percent less than that for the 101 patients treated by the intravenous route (mean [+/-SD], 95.1+/-75.0 vs. 140.3+/-88.5 U per kilogram of body weight per week; P<0.001). Only one patient in the subcutaneous-therapy group withdrew from the study because of pain at the injection site, and 86 percent rated the pain associated with subcutaneous administration as ranging from absent to mild. CONCLUSIONS: In patients receiving hemodialysis, subcutaneous administration of epoetin can maintain the hematocrit in a desired target range, with an average weekly dose of epoetin that is lower than with intravenous administration