Question

why is the uricase method for uric acid often considered preferable to the phosphotungstic acid method?

Answer 1

In phosphotungstic method, the colorimetric reaction involves reduction of phosphotungstate to tungsten blue and oxidation of uric acid. The absorbance measured due to tungsten blue is proportional to amount of uric acid.

In this method, firstly proteins are precipitated from sample, which results in some loss of uric acid.

Also, some other substances such as ascorbic acid, cysteine and thiols may react to produce color.

Hence, the reading does not accurately corresponds to uric acid alone, and results in higher values than actual amount of uric acid.

In case of uricase, method enzymatic oxidation of uric acid occurs. Decrease in absorbance is proportional to dissapperaence of uric acid. No interference of other compounds is possible as the enzyme is specific for uric acid. Hence, the amount measured is accurate by this method.

So, uricase method is preferred.