Objective. Uric acid overexcretion in patients with gout is frequently asse
ssed by the measurement of 24 hour urinary uric acid excretion, which is cu
mbersome with ambulatory patients, and requires accurate timing and complet
e collection of the specimen. We assessed whether uric acid to creatinine r
atio (Uua/Ucr) in spot urine is useful for the estimation of uric acid over
excretion in patients with gout.
Methods. One hundred thirty male patients with gout and 33 non-gout male co
ntrol subjects were studied. Early morning urine and/or a portion of 24 h c
ollected urine (24 h urine) were used as spot urine samples. Uric acid over
excreters were defined as those with a 24 h urinary uric acid excretion gre
ater than or equal to 1000 mg/day, while uric acid underexcreters were defi
ned as those with uric acid clearance < 6 ml/min.
Results. There was a significant relationship between 24 h urinary uric aci
d excretion and early morning urine Uua/Ucr in patients with gout, while no
such relationship was observed in controls. No significant difference in U
ua/Ucr was observed between patients with gout and controls, or in Uua/Ucr
between gout uric acid overexcreters and underexcreters in early morning ur
ine. A significant difference in this value was observed between the 2 grou
ps in the 24 h urine specimens. Although the diagnostic accuracy of gout ur
ic acid overexcretion was 87.2% using early morning urine and 89.6% using 2
4 h urine, the sensitivity of gout uric acid overexcretion was only 25.0% w
hen using early morning urine and 25.0% when using 24 h urine, when the cut
off value of Uua/Ucr was 0.63 and 0.64, respectively.
Conclusion. Uua/Ucr using spot urine, especially early morning urine, is no
t an accurate indicator of uric acid overexcretion in patients with gout.