Improved turbidimetric assay for lysozyme in urine.

I describe an improved turbidimetric assay for lysozyme in urine. This method is simple, reproducible, linear over a 100-fold concentration range, sensitive to concentrations as low as 10 micrograms/L, and only commercially available products are required. Evaluation of urinary lysozyme concentration with this assay demonstrated a within-run and between-run CV of 9.9% and 4.8%, respectively, for normal urine, minimal chemical interference, and a mean analytical recovery of 104.8%. There were differences in the rate of clearing and in the linearity of the assay with use of three commercial preparations of Micrococcus lysodeikticus, and significant differences in results when different lysozyme standards were used. Reference values were established by use of data on 169 healthy subjects, ages six months to 61 years. Clinical efficacy of the assay was demonstrated in children with renal disorders, especially those associated with chronic renal failure or tubular dysfunction.