Detection of inborn errors of metabolism in unselected patients from pediatric intensive care units in Porto Alegre, Brazil: evaluation of screening techniques.

1. The present study provides an analysis of the interpretation and usefulness of mass biochemical urine screening tests currently applied to a population of severely ill children consisting of 232 unselected individuals, under various medications, held in intensive care units. 2. Testing for glycosaminoglycans by the cetyltrimethylammonium bromide reaction is of little benefit to this population. The Ehrlich reaction, used to detect porphobilinogen, should be reserved for cases which present clinical symptoms. Owing to the large number of false-positives and because chromatography or electrophoresis can easily be used to detect tyrosine, it is suggested that the nitrosonaphthol test be abandoned. The cyanide nitroprusside reaction should be used when chromatography or electrophoresis suggests cystinuria, homocystinuria or beta-mercapto lactate disulfiduria. 3. Because of its high sensitivity in detecting reducing substances, the Clinitest is useful for selecting samples to be investigated further by sugar chromatography. 4. Given the relatively high frequency of organic acidurias, particularly methylmalonic aciduria, in intensive care unit populations, it is suggested that the p-nitroaniline reaction be incorporated into the battery of chemical urine tests. 5. A comparison between paper chromatography and high voltage paper electrophoresis in terms of effective analysis of amino acid patterns demonstrated that chromatography is preferential, since this is as sensitive as electrophoresis, does not require a special apparatus and permits the simultaneous use of plasma and urine from the same patient, thus facilitating the interpretation of amino acid patterns.