Sarcopenia, weight loss more common in patients with lower serum urate
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Sarcopenia and weight loss occur more frequently in patients with lower concentrations of serum urate, according to data published in Arthritis & Rheumatology.
However, the link between low serum urate and mortality was found to be non-significant after adjusting for body composition and weight loss, the researchers added.
“Studies in the past have often shown that people with low urate levels have higher risks of some bad outcomes, including early death,” Joshua F. Baker, MD, MSCE, an associate professor of rheumatology and epidemiology at the University of Pennsylvania, in Philadelphia, told Healio. “Concern has thus been raised that low urate levels are thus bad for health, a problem that is of relevance for medications that are extremely good at lowering urate to treat gout.
“We suspected that low urate levels might be observed in people with changes in their body composition — muscle and fat — that are often observed due to poor health,” he added.
To investigate whether low serum urate levels contributed to worse outcomes, Baker and colleagues analyzed data from the National Health and Nutrition Examination Survey from 1999 through 2006, which gathered details about a population representative of the United States. Data were collected through interviews and medical examinations. The researchers categorized serum urate levels using previous definitions of accepted normal ranges. The use of allopurinol, probenecid and diuretic therapy was self-reported on surveys during the study.
Patients were excluded if they were pregnant, weighed more than 300 pounds, were taller than 77 inches, or underwent a recent nuclear medicine scan or exposure to radioactive contrast.
The researchers calculated fat mass index and appendicular lean mass index for included patients using DXA-measured body-composition data. Additionally, they calculated the muscle mass for individuals compared to what would be expected given their present fat mass.
The researchers also used body composition assessments to determine age-, sex- and race-specific appendicular lean mass index and fat mass index Z-scores. Finally, the authors defined sarcopenia and relative sarcopenia using the calculated Z-score, where Z-scores less than or equal to –1 indicated sarcopenia. Mortality data were collected with follow-up through Dec. 31, 2015.
The analysis included a total of 13,979 participants. According to Baker and colleagues, low serum urate concentrations were generally associated with low lean mass, underweight presentation and higher weight loss rates. Among patients with low serum urate levels, 29% demonstrated low appendicular lean mass index Z-scores, compared with 16% of those in the normal serum urate group (P = .001).
Although low serum urate was initially associated with increased mortality (P = .008), this link was later found to be mitigated and non-significant after adjusting for body composition and weight loss (P = .13).
“Low urate levels were observed in patients who were underweight, had low muscle mass and had a history of weight loss,” Baker said. “The key takeaway is that these data should reassure providers that lowering urate levels through medication may not carry risks, though observational data is limited in its ability to prove or disprove causal associations. Gout is often under-treated, and I hope that these data help to promote more aggressive management of hyperuricemia, particularly in patients with more severe, tophaceous gout.”
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