ABSTRACT
In normal men, the urate concentration of plasma averages approximately 5.5G 0.5 mg/dL, whereas that of children and women is lower by about 1 mg/dL.
These levels fluctuate considerably in any individual but always remain in a
rough, overall balance in which the amount of dietary and metabolic urate
entering the system is equaled by the sum of the urinary uric acid together with
the urate of gastrointestinal secretions that is lysed by the uricase of local flora
and excreted as allantoin:
The load may be lowered a little (but not much) by decreasing the dietary
intake or a lot by defective xanthine oxidase, the enzyme responsible for urate
synthesis. This occurs rarely in nature in the form of xanthinuria but often in
practice as a result of xanthine oxidase inhibition by allopurinol. Conversely, the
load will increase with a purine-rich diet, with excessive breakdown of purine
nucleotides (i.e., ATP, GTP, etc.), with accelerated catabolism of cells (as in the
tumor lysis syndrome), or with the rare metabolic defects causing true
overproduction of urate (see also Chapter 12). Each of the above factors affects
the size of the urate burden that is ultimately processed by the kidney or the gut.
Ultimately, however, the most significant determinants of hypo-and
hyperuricemia are not in the load but in the way it is handled.
