Annual change in eGFR in renal hypouricemia: a retrospective pilot study

Extremely low uric acid (UA) levels or increased urinary UA (Uua) excretion might be risk factors for kidney disease in renal hypouricemia (RHU) patients, but their relationship with kidney dysfunction is unclear. This study investigated time-dependent changes in eGFR in RHU patients.

This multicenter retrospective study assessed UA metabolism and changes in eGFR (median 5.5 years) in 13 RHU patients. We then compared eGFR change in 7 of 13 RHU patients whose eGFR could be measured for 4 years with those in normouricemic group (n = 31). In addition, 7 RHU patients were divided into two groups based on URAT1 gene mutations: homozygote and compound heterozygote mutations (Homo/Com group, n = 3), and wild-type and heterogeneous mutations (WT/Hetero group, n = 4).

In 13 RHU patients, the median and mean serum UA (SUA) were 0.8 (0.4-2.5) and 1.1 ± 0.7 mg/dL. The median and mean Uua were 44.3 (12.7-141.1) and 49.7 ± 36.2 mg/dL. The median and mean urinary urate clearance (Cua/Ccr) were 46.8 (11.3-73.6) and 43.3 ± 19.7%. Over 4 years, eGFR did not change in the RHU group but declined in the normouricemic group. Annual mean eGFR decline and change rate in the RHU group were the same as those in the normouricemic group (- 1.09 ± 1.11 vs. - 1.09 ± 1.92 mL/min/1.73 m²/year, p = 0.996) (- 1.74 ± 1.96 vs. - 1.36 ± 2.10%, p = 0.664). And no significant difference was found in eGFR decline or change rate between Homo/Com and WT/Hetero groups (- 0.33 ± 1.03 vs. - 1.67 ± 0.85 mL/min/1.73 m²/year, p = 0.116) (- 0.61 ± 1.62 vs. - 2.59 ± 1.91%, p = 0.210).

RHU from URAT1 genetic mutation may not show eGFR decline over 4 consecutive years.