How variable are hydroxyproline determinations made in different samples of the same liver?

OBJECTIVES The haphazard distribution of fibrous tissue can interfere with quantitative methods for evaluating hepatic fibrosis. Inter-sample variation may represent a crucial issue when hydroxyproline measurement is used to quantify fibrosis. A comparative study of the hydroxyproline levels in normal and fibrotic rats is herein reported. MATERIAL AND METHODS Twelve normal and 20 Capillaria hepatica-infected Wistar rats were used. Two fragments of the liver (A and B) of each rat were taken from separate areas and hydroxyproline measurements were made. Calculated differences in hydroxyproline measurements between samples from the same liver were analyzed by BOOTSTRAP. RESULTS Differences in normal rats varied from 0.026 to 1.85 micromol of HP/g, in ten rats, the difference was less than 0.50 micromol. In infected rats, it varied from 0.04 to 2.86 micromol HP/g. Differences higher than 0.69 micromol/g were significant for normal rats (p<0.05) and above 1.22 micromol/g (p<0.05) for fibrotic rats. CONCLUSIONS Hydroxyproline ratio in a normal liver kept a fair degree of reproducibility. In the presence of hepatic fibrosis, the levels of hydroxyproline may vary significantly between samples from a single liver and may have limited value in quantifying the extent of fibrosis.