Total urinary and free serum hydroxyproline in metastatic bone disease.

The present study examines the possibility of correlation between free serum and urinary total hydroxyproline and whether this correlation can be applied to clinical conditions. The correlation between the two indices was 0.80 (P less than 0.001) in 18 patients, mostly suffering from malignant disease. On comparing the same measurements in 37 patients, all with known metastatic bone disease, we found 29/37 normal results for free serum hydroxyproline, whereas only 2/37 values of urinary total hydroxyproline were normal. The authors therefore conclude that urinary total hydroxyproline, measured as the ratio hydroxyproline/creatinine in a fresh specimen of early-morning urine, is the best index of collagen breakdown in metastatic bone disease and preferable to measurement of free serum hydroxyproline.