Bone and total alkaline phosphatase for screening skeletal metastasis in patients with solid tumours

Alkaline phosphatase (AP) has several isoforms including bone alkaline phosphatase (BAP). We evaluated BAP and AP for screening for bone metastasis (BM) in patients with solid tumours. This is a prospective non-blinded study conducted at ABC Foundation School of Medicine Oncology clinics. A total of 40 subjects without a history of cancer and 62 patients with various solid tumours referred for a bone scan had serum drawn for BAP and AP determination. Bone alkaline phosphatase and AP levels in patients with cancer and BM, without BM and with no cancer, were 70.32 +/- 3.65 and 310.21 +/- 16.87 U/L; 41.40 +/- 2.80 and 113.23 +/- 12.95 U/L; 21.19 +/- 2.76 and 148.05 +/- 12.79 U/L respectively (P < 0.0001 for both AP and BAP). For BAP and AP sensitivity, specificity, positive and negative predictive values were 0.86 and 0.52; 0.69 and 1; 0.45 and 1; 0.94 and 0.87 respectively. ROC AUC value for BAP was 0.89 and for AP was 0.93. We conclude that BAP is more sensitive than AP, whereas AP had a remarkable specificity of 100%. In screening for BM in patients with solid tumours, obtaining initially BAP and then selecting for further investigation only patients with an abnormal AP may be a cost and resource saving strategy.