Measurement of free and total hydroxyproline by automated flow injection of serum or urine samples from maintenance hemodialysis patients with renal osteodystrophy.

An automated measurement of total and free hydroxyproline in serum or urine is presented that uses flow injection analysis. After exclusion of nonspecific substances, hydroxyproline was oxidized by chloramine-T and L-cysteine with Ehrlich's reagent. The linearity obtained was from 3.8 mumole/L to 1.22 mmole/L with good precision (CV < 3%). Comparison of the proposed method with HPLC yielded r = 0.939 as the correlation coefficient. Reference intervals of free and total hydroxyproline are 1.4-9.7 mumole/L, 3.8-27.2 mumole/L for serum, and 10.0-72.5 mumole/L, 25.2-303.6 mumole/L for urine, respectively. Serum free and total hydroxyproline levels in renal osteodystrophy patients on maintenance hemodialysis (N = 71) were significantly higher than in controls (P < 0.0001). This method is superior to the use of HPLC with regard to stability of the color reaction. The measurement of serum free and total hydroxyproline is a useful marker for therapeutic observation of renal osteodystrophy patients.