Abstract

Autosomal-dominant acute porphyria, a group of rare metabolic diseases, can lead to life-threatening neurovisceral attacks. Currently, no efficient screening test is available. Elevated urinary porphobilinogen (PBG) in addition to elevated porphyrins is highly specific for an attack of acute porphyria. This study proposes and evaluates a custom-made device, algorithm, and methods for a two-step quantification of urinary porphyrins and PBG.

The first step is oxidation of the nonfluorescent porphyrinogens and subsequent fluorescence-spectroscopic determination of total urinary porphyrins (TUP) using second derivative spectral fitting. Photo-oxidation is compared with chemical oxidation methods. The second step is the quantification of porphobilinogen in case of elevated TUP. Heat-induced conversion products of PBG, namely uroporphyrin and porphobilin, are determined by fluorescence and absorption spectroscopy.

The results of TUP quantification using the developed second derivative fitting algorithm show that both inaccuracy and imprecision were below 15% for concentrations of 0.2 µmol/L and higher. Heating of PBG generates porphobilin, which was detected using its absorption at 480 nm, and uroporphyrin, which was detected using its fluorescence at 615 nm. The change of fluorescence and absorption allows for a quantitative discriminability of PBG concentrations below 20 mg/L. For this indirect quantification of PBG, the resulting inaccuracy and imprecision are below 15% for both methods.

The detection and quantification of TUP and porphobilinogen in urine with this proposed spectrophotometric approach is possible, requires only minimal sample processing and yields a result within 15 min, thus could be helpful in closing the screening gap for acute porphyria.

© 2019 SPIE/OSA