SAN FRANCISCO – Assessing renal health using a modified Cockroft-Gault equation to measure creatinine clearance was more sensitive than using the Modification of Diet in Renal Disease equation to estimate glomerular filtration rate when estimating risk for osteoporosis and fracture, an award-winning study of 400 postmenopausal Puerto Rican women showed.
The study found a high prevalence of mild renal dysfunction (stage 2 chronic kidney disease) in 54%-59% of women, depending on the equation used. With the Cockroft-Gault equation adjusted for body surface area, a determination of mild renal dysfunction was associated with significantly decreased bone mineral density and with a doubling in risk for vertebral or nonvertebral fractures. When the Modification of Diet in Renal Disease (MDRD) equation was used, however, no significant associations were found between mild renal dysfunction and fracture risk, Dr. Loida A. González-Rodriguez reported.
Dr. Loida González-Rodriguez
Previous data have shown that severe renal dysfunction is associated with reduced bone mineral density and fractures, and that a creatinine clearance below 65 mL/min per 1.73 m2 is associated with a higher risk for falls and hip fractures in elderly people. Less is known about the effects of mild renal dysfunction on bone mineral density.
"We are postulating that this Cockroft-Gault equation is better to estimate bone," because it includes factors such as weight and age, and is adjusted for body surface area, Dr. González-Rodriguez said in an interview at the annual meeting of the Endocrine Society. She received an award at the meeting for her retrospective secondary analysis of data from the Latin American Vertebral Osteoporosis Study, the first population-based study of vertebral fractures in Latin America.
Many clinicians use the MDRD equation to estimate renal function. Dr. González-Rodriguez of the University of Puerto Rico, San Juan, said she has switched to using the Cockroft-Gault equation, and is trying to get colleagues at her institution to do the same. The MDRD equation will miss some patients who are at risk for osteopenia, osteoporosis, and fracture, she said.
Seventeen percent of patients in the study had normal bone mineral density, 43% had osteopenia, and 41% had osteoporosis. (Percentages were rounded and so exceed 100%.)
When the Cockroft-Gault equation was used to categorize renal function, 9% of patients had stage 1 chronic kidney disease, 54% had stage 2, 35% had stage 3, and 2% had stage 4. When the MDRD equation was used, 2% of patients had stage 1 chronic kidney disease, 59% had stage 2, 38% had stage 3, and 1% had stage 4.
Among patients with stage 2 chronic kidney disease as assessed by the Cockroft-Gault equation, 19% had normal bone mineral density, 49% had osteopenia, and 32% had osteoporosis. Among patients with stage 2 disease assessed using the MDRD equation, 4% had normal bone mineral density, 35% had osteopenia, and 60% had osteoporosis.
Vertebral fractures occurred in 9% and nonvertebral fractures occurred in 18% of patients with stage 2 disease assessed with the Cockroft-Gault equation. When the MDRD equation was used, 9% of patients with stage 2 disease developed vertebral fractures and 24% developed nonvertebral fractures.
Among patients with stage 3 chronic kidney disease assessed using the Cockroft-Gault equation, 18% developed vertebral fractures and 31% developed nonvertebral fractures, compared with vertebral fractures in 16% and nonvertebral fractures in 22% of patients with stage 3 disease assessed using the MDRD equation.
"One of the most important risk factors for vertebral and nonvertebral fractures is osteoporosis," Dr. González-Rodriguez noted. "So, if we can identify earlier the patients that have mild renal dysfunction" using the Cockroft-Gault equation and manage the osteoporosis risk, some fractures may be prevented.
The findings are limited by the retrospective design of the study, a lack of blood pressure measurements to assess arterial hypertension, self-reported nonvertebral fractures, and a lack of measurements of intact parathyroid hormone, 25-hydroxyvitamin D, and microalbuminuria.
Dr. González-Rodriguez reported having no relevant financial disclosures. The National Center for Research Resources and the National Institute on Minority Health and Health Disparities funded the study.
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