Serum uric acid and mortality risk among maintenance hemodialysis patients

the general population has changed since the 1950s [1]. Hyperuricemia was originally considered to be a consequence of renal insufficiency and associated with a variety of cardiovascular diseases, and several studies suggested that hyperuricemia can cause hypertension, renal insufficiency and metabolic syndrome. However, the role of serum uric acid remains unclear in the maintenance hemodialysis (MHD) patient population. In the MHD population, traditional cardiovascular risk factors, such as body mass index (BMI), serum cholesterol, and blood pressure were paradoxically associated with better outcomes [2]. This evidence for “reverse epidemiology”, is partly explained by the presence of ‘malnutrition-inflammation complex syndrome’ among the MHD patients. Uremic malnutrition, which is now referred to as “protein-energy wasting” (PEW), leads to low BMI and hypocholesterolemia and is common in dialysis patients. PEW is caused by inadequate nutrient intake, nutrient loss during dialysis, hyper-catabolism associated with dialysis, metabolic acidosis, and endocrine disorders of uremia. PEW has wide overlap with inflammation and other etiologic factors which can be used as assessment tools; this association between PEW and inflammation is believed to be the main cause of cardiovascular disease. Recently, the role of uric acid has also been re-evaluated in the context of other traditional and non-traditional risk factors in the MHD population. Several studies have found that serum uric acid concentrations were closely correlated with nutritional parameters, including dietary protein intake as measured by normalized protein catabolic rate (nPCR), BMI, albumin and phosphorus and that low serum uric acid concentrations were associated with higher mortality, especially among patients with lower protein intake as reflected by nPCR [3]. Furthermore, nPCR underestimates protein intake among patients with substantial residual renal function if renal urea clearance is not taken into account; therefore, serum uric acid may be an alternative laboratory marker of nutrition intake, compared to nPCR, when patients have substantial residual renal function. The relationship between low serum uric acid and ‘malnutrition-inflammation complex syndrome’ may be responsible for this newly discovered ‘reverse epidemiology’ phenomenon. In this issue of Kidney Research and Clinical Practice, Kim et al [4] examined the relationship between serum uric acid concentrations with all-cause mortality using a retrospective analysis of the data from 7,333 MHD patients documented in the End-Stage Renal Disease Serum uric acid and mortality risk among maintenance hemodialysis patients Inkyong Hur, Soo Jeong Choi, Kamyar Kalantar-Zadeh Harold Simmons Center of Kidney Disease Research and Epidemiology, Division of Nephrology and Hypertension, University of California Irvine School of Medicine, Orange and Irvine, CA, USA Division of Nephrology, Semyeong Christianity Hospital, Pohang, Korea Division of Nephrology, Soonchunhyang University College of Medicine, Bucheon, Korea Long Beach VA Healthcare System, Long Beach, CA, USA Los Angeles Biomedical Research Institute at Harbor-UCLA, Torrance, CA, USA Department of Epidemiology, UCLA Fielding School of Public Health, Los Angeles, CA, USA Editorial