Evaluation of a first-line spectrophotometric screening test for increased faecal porphyrin concentration.

We compared a spectrophotometric screening test measuring faecal porphyrin concentration with an HPLC method. There was a good overall correlation between both methods although some scatter was observed. ROC plot analysis of the screening test leads to a cut-off value of 35 nmol porphyrin per g faeces, wet weight with a sensitivity of 97% and a specificity of 96%. These results indicate that the screening test is quite useful for detection of increased total faecal porphyrin concentration, but less useful in accurate measurement of increased total faecal porphyrin concentration.