However, most plain radiographs will not be diagnostic of cancer when it presents at an early stage, in the form of back pain. The most sensitive general test for bone involvement with cancer is the bone scan. This test is of limited usefulness for musculoskeletal back pain and thus poses a testing dilemma. Although laboratory testing of blood is never the only diagnostic tool which is appropriate to diagnose cancer, there are several blood tests which, if abnormal, will be particularly useful to guide your subsequent diagnostic and referral activities. Alkaline phosphatase is a good test for liver obstruction or bone metastasis, and fractinated isoenzymes can differentiate between these two sources.
Acid phosphatase remains a very useful tool for diagnosis of prostate cancer.
However, a negative test does not rule out prostate cancer. Among urologic oncologists, prostatic acid phosphatase has almost been replaced by the PSA when the purpose is to monitor response to therapy. A normal acid phosphatase should never be used in place of a digital examination of the prostate. This is because the digital examination itself may cause a transient rise in serum levels. Any palpable abnormality should be considered for fine needle aspiration in order to make a cytologic diagnosis.