Zusammenfassung
A programme for proficiency testing of biochemical
genetics laboratories undertaking urinary qualitative
organic acid analysis and its results for 50 samples
examined for factors contributing to poor performance are
described. Urine samples from patients in whom inherited
metabolic disorders have been confirmed as well as control
urines were circulated to participants and the results from
94 laboratories were evaluated. Laboratories showed
variability both in terms of their individual performance
and on a disease-specific basis. In general, conditions
including methylmalonic aciduria, propionic aciduria,
isovaleric aciduria, mevalonic aciduria, Canavan disease
and 3-methylcrotonyl-CoA carboxylase were readily
identified. Detection was poorer for other diseases such as
glutaric aciduria type II, glyceric aciduria and, in one
sample, 3-methylcrotonyl-CoA carboxylase deficiency. To
identify the factors that allow some laboratories to
perform well on a consistent basis while others perform
badly, we devised a questionnaire and compared the
responses with the results for performance in the scheme. A
trend towards better performance could be demonstrated for
those laboratories that regularly use internal quality
control (QC) samples in their sample preparation (p =
0.079) and those that participate in further external
quality assurance (EQA) schemes (p = 0,040). Clinicians who
depend upon these diagnostic services to identify patients
with these defects and the laboratories that provide them
should be aware of the potential for missed diagnoses and
the factors that may lead to improved performance.
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