We compared five methods for the determination of total and direct bilirubins in serum samples from normal controls, subjects with Gilbert's syndrome, and serum pools containing about 50 and 150 mg of total bilirubin per liter. The Kodak Ektachem method and a diazotized sulfanilic acid method with 0.15 mmol/L sodium nitrite concentrations are the only methods that gave accurate direct bilirubin values, as judged by liquid-chromatographic results. The aca method that involved p-nitrobenzene diazonium tetrafluoroborate and another diazotized sulfanilic acid method with a higher concentration of sodium nitrite (0.8 mmol/L) yielded falsely high values for direct bilirubin, which could lead to clinical confusion. The more recently introduced diazotized sulfanilic acid method of the aca gave substantially better results than the p-nitrobenzene diazonium tetrafluoroborate method but was still inaccurate. Systematic investigation of these procedures revealed that the overestimation of direct bilirubin by the diazotized sulfanilic acid method was related to the amount of unconjugated bilirubin present and its ability to react as direct bilirubin in the presence of higher concentrations of sodium nitrite. Inherent properties of p-nitrobenzene diazonium tetrafluoroborate appeared to be responsible for inaccuracies in that method, which could not be corrected by varying reagent concentration or the reaction conditions.
Pyroglutamic acidemia, a rare metabolic disorder, usually appears in infancy. It is characterized by retardation, ataxia, hemolytic anemia, and chronic acidosis and is caused by a marked deficiency of glutathione synthetase (EC 6.3.2.3) activity. This disease is inherited as an autosomal recessive trait, but the clinical condition is also detected in heterozygotes. We report an unusual case of high-anion-gap metabolic acidosis in a 52-year-old woman who was admitted with neurological complaints and breathing problems but without the characteristic clinical features of congenital glutathione synthetase deficiency. The etiology of the acidosis could not be attributed to ketoacidosis, lactic acidosis, or ingestion of methanol, salicylate, or ethylene glycol. Analysis of the patient's plasma and urine for organic acids revealed the presence of high concentrations of pyroglutamate (5-oxoproline), which remained high throughout her hospitalization.
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