A novel assessment method of serum alkaline phosphatase for the diagnosis of osteosarcoma in children and adolescents

A high serum alkaline phosphatase (ALP) level is valuable for the diagnosis of osteosarcoma in adults, but its use in teenagers is problematic because ALP levels are affected by age, gender, and pubertal stage. Because serum acid phosphatase (ACP) shows the same tetraphasic pattern as serum ALP in children and adolescents, we presumed that serum levels of ALP and ACP would have a strong correlation and that the ratio of ALP to ACP (ALP/ACP) would show little variation and would be useful for the diagnosis of osteosarcoma in teenagers. The purpose of this study was to evaluate the correlation between the serum levels of ALP and ACP and to investigate the validity of ALP/ACP in the differential diagnosis of osteosarcoma in children and adolescents.

We retrospectively examined 538 patients aged 1–18 years, including 24 with osteosarcomas, 8 with other malignant bone tumors, 56 with benign bone tumors, and with 450 non-tumor lesions (controls). We evaluated the serum levels of ALP and ACP, both obtained by preoperative examination.

There were significant correlations between the serum ALP and ACP levels in the controls (r = 0.805 in males and r = 0.860 in females). The ratios of ALP to ACP in the controls showed little variation with age. In ROC curve analysis, to discriminate between the osteosarcomas and the controls, the cutoff levels of serum ALP and ALP/ACP were 956 (U/l) and 50.9 in males and 748 (U/l) and 43.3 in females, respectively. The sensitivity and specificity of serum ALP and ALP/ACP in the differential diagnosis of osteosarcoma were 50.0 and 89.0 %, and 60.0 and 94.1 %, respectively in males, and 61.5 and 72.7 %, and 69.2 and 84.2 %, respectively, in females.

The results suggest that ALP/ACP is more useful than the serum ALP level in diagnosing osteosarcoma because it is little affected by the age.