Lowered Endogenous Uric Acid Output
As a rule, gouty subjects, on a purin-free diet, excrete less endogenous uric acid than normal persons. Thus, according to Walker Hall, the average daily endogenous urinary uric acid output of a normal adult is about 0·5 gramme, while that of a gouty subject is about 0·45 gramme. Brugsch and Schittenhelm hold that in about 80 per cent. of cases the average endogenous excretion is lower than normal.[19]
According to these same observers, “the maximum fluctuation during attack-free periods was at first believed to be less than in the normal cases; more recent examinations, however, have shown that in the same case of gout there may be periods of high, and periods of low, endogenous uric acid excretion.” These variations, they hold, are not to be accounted for by either mild or severe attacks of gout, for they occur in the attack-free period.
Again Laird, investigating the elimination of endogenous uric acid in a case of chronic gout, noted that the output thereof was sub-normal, and, as Brugsch and Schittenhelm observed, the same presented marked variations. The leucocyte counts he found normal, but the phosphorus output and the acidity were sub-normal. Bloch again, while he agrees that endogenous purin excretion is usually below the average in gouty subjects, found that the output thereof is at its minimum before an acute attack of gout.
The foregoing observations would suggest that the retention or delayed excretion of uric acid applies both to exogenous and endogenous purins. But, when we come to analyse the foregoing findings as to the variations in uric acid output, both in acute and chronic gout, one feels inclined to agree with O. Folin, “that the clinically useful contributions obtained by urine analysis have not been very numerous.” Thus we cannot, on the basis of the variations in uric acid excretion, presume to diagnose gout; in other words, if we take urine analysis alone, it is extremely difficult to prove that the uric acid elimination in gout is really and truly abnormal. Our uncertainty, moreover, is the more pronounced when we realise that in some cases of rheumatoid arthritis, etc., there is a disturbance of purin metabolism which in some of its features is reminiscent of that obtaining in typical gout. But, before proceeding to discuss this interesting resemblance, it will, we think, be convenient here to recall that the obliquities in metabolism found in gout are not wholly restricted to uric acid.