The link of O2 to the haeme structure in haemoglobin can initiate free radical formation. Some reducing substances, e.g. ascorbic acid, have an antioxidant effect on free radicals but paradoxically they can participate also in mechanisms of their formation. By acceptance of one O2 electron in oxyhaemoglobin potentially not only the formation of methaemoglobin is induced but also of H2O2 and other free radicals, e.g. by dissociation mechanisms of the ferrihaeme complex. The authors analyzed therefore the possible genesis of free radicals and their effect on the characteristic of the fluorescent background of the erythrocyte when assessing the erythrocytic zinc-protoporphyrin (ZPP) by the method of front-face haematofluorometry after direct oxidative stress of the erythrocyte by H2O2 and ascorbic acid in vitro. The highly significant change of autofluorescence of the erythrocyte attained by oxidative stress in the model experiment raises the question of the importance of possible damage of this blood cell in vivo. When evaluating the relevance of the assessed value of the ZPP concentration in the erythrocyte by direct haematofluorometry an important role may be played by interference erythrocyte fluorescence (IEF). Therefore some aspects of this phenomenon are discussed as well as the prooxidative effect of ascorbic acid and free radical formation.

        Key words: haematofluorometry, interference fluorescence, zinc-protoporphyrin, ascorbic acid, oxidative stress, methaemoglobinaemia.