A simple lysoplate method of lysozyme determination with samples dried on filter paper

A simple method for quantifying lysozyme in serum and urine has been established by modifying the procedures of sample application in the lysoplate method reported by Osserman and Lawlor [1]. A strip of filter paper is partially immersed in a liquid sample, dried at room temperature and cut into discs which are later placed on the surface of an agarose gel containing Micrococcus lysodeikticus. The following procedures for determination are carried out as described in the lysoplate method. There was no statistically significant loss of enzyme activity during the sample preparation. Lysozyme dried on filter paper is so stable that it can be stored at room temperature for at least 13 weeks and can be mailed. The sensitivity of the method is increased by pretreatment of the filter paper with Triton X-100 and consequently corresponds to that of the lysoplate method. The reproducibility of our method is practically good since the variation coefficient of the diameters of lytic zones within assays is around 1%. There is a very close correlation between lysozyme levels determined by this method and by the lysoplate method with serum samples obtained from patients with various hematological diseases (r = + 0.994). The method can be utilized for routine clinical determinations of lysozyme.