RESUMO
BACKGROUND: Succinylacetone (SUAC) is the primary metabolic marker for hepatorenal tyrosinemia. MATERIALS AND METHODS: We used results reported for dried-blood-spot proficiency testing (PT) specimens and hepatorenal tyrosinemia patients' newborn screening (NBS) samples to demonstrate analytic biases in SUAC recoveries and differences in presumptive clinical classifications. RESULTS: SUAC recoveries from non-kit and NeoBase™ kit tandem mass spectrometry methods were markedly different. Kit users that set high cutoff values submitted discordant clinical assessments of "within normal limits" for PT specimens enriched with 10-15 µmol SUAC/L in blood. SUAC levels in tyrosinemia patients' NBS samples analyzed by NeoBase™ kit were lower than those in samples analyzed by non-kit methods. CONCLUSIONS: From 2009 to 2011, analytic biases in SUAC recoveries were consistent. Discordant clinical assessments of PT specimens were associated with high cutoff values for NeoBase™ kit results. Method-related differences in SUAC concentrations of tyrosinemia patients' samples were consistent with those of PT specimens.
