Evaluation of the activity of tartrate-resistant acid phosphatase isoform 5b in normal Chinese children--a novel marker for bone growth.

Background: Most parents are very concerned about the height of their children. Biochemical markers of bone formation and resorption may provide useful clinical predictors for bone growth. Tartrate-resistant acid phosphatase 5b (TRAcP 5b) has been advocated as a biomarker of osteoclast activity and bone resorption. However, the TRAcP 5b levels of children at different ages are still unknown. It is necessary to accumulate and analyze the data for healthy children at different ages.

Objectives: We use an improved immunoassay for bone TRAcP 5b to examine sera from children to see whether it is a significant marker of bone growth.

Methods: Serum, including cord blood, was collected from 404 normal Chinese children (age range 0-17 years; 225 male, 179 female). The venous blood was withdrawn from the peripheral vein and stored at 4 degrees C before centrifugation for serum collection. All sera were stored at -70 degrees C and thawed at 37 degrees C immediately before TRAcP 5b levels were measured. Bone-specific alkaline phosphatase (BAP) was also used for comparison with TRAcP 5b levels at different ages.

Results: TRAcP 5b levels were extremely high in infants of both genders, gradually decreasing with age (p <0.001). A second peak in TRAcP 5b values occurred at 12-13 and 10-11 years in males and females, respectively (p <0.001). Age alone, as well as age-related changes between the male and female groups, were independent predictors of TRAcP 5b levels (p <0.001). There was no significant between-gender difference in serum TRAcP 5b levels for any age group (p = 0.682). BAP values did not show a significant second peak in females. Age and gender alone, as well as the age-related changes between male and female groups, were independent predictors of BAP values (p <0.001).

Conclusion: Preliminary results were established for serum TRAcP 5b and BAP values of normal Chinese children of different ages. Elevated serum TRAcP 5b values were observed during infancy and puberty for both genders. The pattern of this age-related change in serum TRAcP 5b levels is similar to the shape of the standard height velocity curve for healthy children. Values of BAP were less specific than TRAcP 5b. These data may prove valuable as a normal reference in future research about bone markers.