Conditions Affecting the Colorimetry of Orotic Acid and Orotidine in Urine

We studied conditions affecting a colorimetric assay of totaloroticacid(oroticacid plusorotidine) inurine.Most interfering substances can be conveniently removed on a small column of cation-exchangeresin,and an improved controlreactioncorrectsfor residualbackground color. Analytical recoveryfrom urineisnearly complete (>95%) and the absorptionspectrum foranalyteelutedfrom the column closelyresembles thatforan oroticacid standard. We determined reference intervalsfortotaloroticacid, expressed as a molar ratioto creatinine,forneonates, children,and adults,and assessed the effectofage,protein intake,and pregnancy. The method issimple enough to use as a reliable and accurate urine-screening test. AdditIonal Keyphrases: reference intervals screening defects in pyrimidine biosynthesis. hyperammonemi