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Spot urine test reliably indicated kidney efficiency in urate removal
Spot fractional renal clearance of urate was a convenient, valid and reliable indicator of kidney efficiency in removing urate from blood and tissues, according to study results.
Researchers used four substudies in their investigation:
- Twelve healthy participants were evaluated, using timed (spot, 2-, 4-, 6-, 12- and 24-hour) urine collections to derive fractional renal clearance of urate (FCU). Blood samples were drawn midway through the 24-hour period.
- Thirteen healthy participants produced spot urine samples twice daily during three nonconsecutive days to measure FCU. Blood was drawn each morning.
- Eleven healthy participants were assigned three treatments of up to 7 days of allopurinol (150 mg, twice daily), probenecid (500 mg, twice daily) or allopurinol plus probenecid (150 mg and 500 mg, respectively, twice daily). Plasma was taken eight times daily; urine samples were taken before treatment and on day 8.
- Thirty-six patients with gout assigned allopurinol had FCU measured in blood and urine.
Eighty-five healthy men also provided single plasma and spot urine samples. FCU distribution then was examined in 118 healthy controls compared with the gout patients. Researchers saw:
- FCU derived from spot (7.4%) and 24-hour (6.9%) urine collections showed no substantive or statistical differences (inter-participant coefficient of variation [CV], both 28%).
- Spot FCU obtained either within or between days also showed no significant CV differences (mean intra-participant CV, 16.4%).
- Probenecid and allopurinol/probenecid participants saw nearly threefold increases in FCU (P<.05). FCU changes among allopurinol participants were not significant.
- FCU in healthy allopurinol participants and those with gout remained static; controls had greater mean FCU than gout patients (6.9% vs. 4.8%, P<.0001).
“FCU derived from a spot, daytime urine sample is a valid methodology providing an estimate of FCU not different from FCU estimated using the traditional 24-hour urine collection,” the researchers said. “Spot FCU determinations may provide useful correlates in studies investigating molecular mechanisms underpinning the observed range of efficiencies of the kidneys in clearing urate from the blood.”