[Techniques for studying collagen in medical practice].

A brief description of the structure of collagen and the special features of each type of collagen, followed by a summary of its metabolism, serve as an introduction to the major pathological processes involving the collagen molecule; mutations, inflammatory syndrome bone diseases, basement membrane diseases. The measurement of hydroxyproline isomers in urine is the basic biochemical test for diseases involving the collagen molecule. 4-hydroxyproline is increased in bone disease of Paget and in cancerous metastases of bone, 3-hydroxyproline is increased in case of polycystic kidney. It is possible, but not very useful, to measure serum 4-hydroxyproline. Of more interest, is the radio-immunological measurement of the N-terminal extension of the type III procollagen molecule, which can differentiate ordinary hepatitis from cirrhogenous hepatitis. New and useful information can be gained from tissue biopsy: the proportion of the various types of collagen, the measurement of their hydroxylation and the activity of the enzymes acting on their biosynthesis.