Current trend and risk factors for kidney stones in persons with spinal cord injury: a longitudinal study
Study design: A multi-center longitudinal study.Objectives: To estimate the current trend in the incidence of first kidney stone among persons with spinal cord injury (SCI) and to delineate the potential contributing factors.Setting: Twenty-one Model SCI Care Systems throughout the United States.Methods: A longitudinal cohort of 8314 subjects enrolled in the National SCI Database between 1986 and 1999 was used to estimate and compare the incidence of first kidney stone with a previous report of 5850 SCI patients injured between 1973 and 1982. A Cox regression analysis was performed to identify risk factors for stones, including age, race, gender, severity of injury, and method of urinary drainage. These variables have been routinely collected, on a yearly basis, by the collaborating SCI centers.Results: During the 12 years, 6 months of case ascertainment, 286 incident stone cases were documented. The risk was greatest during the first 3 months after injury (31 cases per 1000 person-years), quickly decreasing and leveling off later (eight cases per 1000 person-years). It was estimated that within 10 years after injury, 7% of persons with SCI would develop their first kidney stone. There was no evidence that the risk has changed over the past 25 years (P=0.96). During the first year post injury only, a significantly increased risk of stones was observed in Caucasians and persons aged 45 years or older. A positive association of the severity of injury and requiring instrumentation for bladder emptying with kidney stones was found after the first year post injury. The type of urinary drainage, including indwelling, intermittent, and condom catheterization, had no significant differential effect on stone formation at either risk period.Conclusions: The highest risk of kidney stones is within the first few months post injury. Little progress has been made in reducing this risk. Although inability to control bladder function is an important risk factor after the first year post injury, for those who need bladder management, the type of urinary drainage does not appear to be an important factor in determining risk.