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(10) Prostate Disorder

What is free PSA?

For reasons that are not totally understood, PSA that is made by prostate cancer cells is preferentially bound to a serum protein known as alpha-1-antichymotrypsin, whereas PSA elaborated by benign prostate cells is free or unbound. Most laboratories now provide the fraction of free PSA as a percentage of the total PSA.

Again, assays may vary from laboratory to laboratory, but generally, a free fraction of 25 percent or more is considered consistent with benign disease.

When a patient has a PSA test of his blood, should he always ask his doctor to include a test of free PSA and complex PSA?

No, this should be left up to the judgment of the urologist.

Calculations of free PSA are most useful in men who have had an elevated PSA in the past with negative biopsies. If the total PSA remains elevated and the free PSA fraction is depressed, the urologist is more likely to recommend a repeat biopsy.

What is complexed PSA?

Complexed PSA is an assay that measures the PSA that is bound to alpha-1-antichymotrypsin. In a sense, it is the converse of free PSA. Some reports have advocated the use of complexed PSA to help differentiate cancer of the prostate from BPH; however, its superiority to the standard total and free PSA calculations has not been conclusively proven. In addition, not all laboratories offer complexed PSA measurements.

What is HK2?

Human glandular kallikrein (HK2) was first isolated from seminal plasma in the ejaculate. HK2 is similar to but distinct from PSA. Some experimental studies have demonstrated that HK2 measurements may be helpful in differentiating malignant from benign prostate disease; however, the role of HK2 is not fully understood, and its measurement is only available through certain research facilities. It is not currently used clinically.

What is acid phosphatase?

Acid phosphatase is an enzyme found in the blood that is made primarily by the prostate gland. Before the PSA era, it was the only prostate cancer marker available, and like PSA, acid phosphatase is made by both benign and malignant prostate tissue; however, acid phosphatase levels can vary markedly and are not as reliable a marker as PSA. Acid phosphatase is no longer used today in the diagnosis and management of prostate cancer.

Terms:

Alpha-1- antichymotrypsin substance in the blood that can bind PSA.

Complexed PSA - PSA that is bound to alpha-1-antichymotrypsin.

Human glandular –a substance made by the prostate gland that is not used as a tumor marker

Acid phosphatase - tumor marker for prostate cancer that is no longer used.

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