Precision and accuracy of a HPLC method for measurement of fecal porphyrin concentrations.

We studied precision and accuracy of a HPLC method for determination of porphyrins in feces. A commercial standard solution appeared to contain less coproporphyrin (15%) than stated by the manufacturer. The between-batch coefficients of variation were often below 15% and were higher than the within-batch coefficients. The precision of porphyrin measurements was not influenced by the type of porphyria. Recoveries of added coproporphyrin and protoporphyrin were 90% and 108%; coefficients of variation were 6% and 19%, respectively.