Biochemical bone markers compared with bone density measurement by dual energy X-ray absorptiometry.

In contrast to medical imaging, the biochemical markers allow a more frequent determination and are not as invasive as histomorphometric methods. We investigated biochemical markers of type I collagen compared with bone density measurements in 85 females between 41 and 89 years of age (median: 57 years). The bone density measurements were performed by dual energy X-ray absorptiometry (DXA) on the lumbar spine (L1-4). The bone density measurements were stated as a percentage of the norm. All patients were divided into three groups: I = <80%; II = 80-130%; III = >120%. Based on this classification the median concentration of the I-carboxyterminal propeptide of type I collagen in serum (S-PICP) as an anabolic marker of type-I collagen increased significantly with rising bone density: I 65.0 micrograms/liter (interquartile range: 52.1-78.0 micrograms/liter); II 85.9 micrograms/liter (52.1-115.5 micrograms/liter); III 81.4 micrograms/liter (62.0-101.0 micrograms/liter);P < 0.05. The concentration of urinary pyridinolines (U-PYR) as a marker for degradation of type I collagen decreased. The I-carboxyterminal telopeptide (S-ICTP) and osteocalcin (S-BGP) did not change. The multivariate regression analysis showed no relationship between between bone density and biochemical bone markers. Only the age significantly correlated negatively with bone density measurement. For a better assessment of type I collagen metabolism we created a "b-quotient" by dividing the sum of S-PICP and S-BGP by U-PYR. The median b-quotient increased significantly: I 1.55 (0.97-2.04); II 2.09 (1.57-2.86): III 2.46 (1.58-3.22); P < 0.05. Changes in bone metabolism cannot be identified by the determination of a single marker. However, the improved biochemical diagnostic measurement using the b-quotient may provide early information about the progression of a metabolic disorder within the interval of imaging.