Back
Previous studies have found an increased relative risk of 1.5-2 for a faster renal function deterioration or chronic kidney disease with serum uric acid (UA) level elevation. The association of baseline urinary uric acid (UAA) level with renal function decrease is unknown. The aim of our study is to assess this relation. UAA might be a better parameter than serum UA to predict renal function change, as it reflects UA levels through all day hours, not just before serum sampling and because its direct impact on renal parenchyma.
In this retrospective cohort controlled study we included patients treated in Haifa and the Western Galilee district of Clalit Health Services in Israel, who were compatible, with the following inclusion criteria: age above 18 years old, the presence in their electronic medical records of at least one UAA level and two eGFR (estimated glomerular filtration rate, according to epi-CKD formula) values, at least one year between them, the baseline eGFR value being up to one year after the earliest UAA level. Exclusion criteria were chronic dialysis treatment before the baseline eGFR and kidney transplantation at any time. In the study group were included patients with at least one baseline UAA level that is ≥ 750 mg/day and without any UAA level later on that is below this value and in the control group were included patients that all their UAA levels were < 750mg/day. The baseline variables of the participants, which had been assessed in the past as part of a routine follow-up or because of any other unknown reason, were obtained from their medical and laboratory records. The change between the nearest eGFR to the earliest UAA and the latest eGFR was calculated for each group. In patients who started dialysis the eGFR before dialysis initiation was considered the latest. The primary endpoint was the composite of decline in eGFR of at least 50%, eGFR < 15 ml/minute, dialysis initiation or death. The baseline characteristics of the two groups were compared by Chi square test for categorial variables and independent t-test for continuous variables. The endpoint was compared between the groups by multivariable logistic regression adjusted to age, male sex, presence of hypertension, diabetes mellitus, congestive heart failure or urinary calculi, treatment by allopurinol, baseline eGFR, and the follow-up duration.
In the study group were included 480 patients and in control group 2998. The mean age of each group was 54.8 and 63.2 years respectively. 374 (77.9%) of the study group and 1694 (56.5%) of the control group were males. Additional characteristics of the participants are shown in table 1. The primary endpoint was found in 928 (30.9%) of the control group and in 78 (16.2%) of the study group. After adjustment by logistic regression the odds ratio was 0.971 (95% confidence interval 0.717-1.31, p= 0.8462).
There was no significant difference in the composite endpoint of decline in eGFR of at least 50%, eGFR < 15 ml/minute, dialysis initiation or death between patients with baseline hyperuricosuria (UAA≥ 750 mg/day) and those without it. Further prospective studies may clarify the role of uricosuria in renal function deterioration.