BACKGROUND: We evaluated a quality control scheme for the measurement of urinary uroporphyrin, coproporphyrin, total urinary porphyrins and precursors of urinary porphyrins, delta-aminolevulinic acid and porphobilinogen that was performed in The Netherlands during a period of 5 years.
METHODS: Six quality control samples were distributed each year to the participating laboratories. Mean concentrations and the corresponding coefficients of variation were calculated.
RESULTS: Coefficients of variation varied widely and were very high in the concentration ranges that can be found in patients with low-grade porphyria.
CONCLUSIONS: Commutable calibrators are needed to improve the laboratory diagnosis of porphyria.