Digital rectal examination (DRE) and PSA (Prostate Specific Antigen) blood test are the two most important tests in screening for prostate cancer.
What is Prostate Specific Antigen (PSA)
Prostate Specific Antigen (PSA) is a protein made by the prostate that enters the blood stream. PSA is reported in nanograms per milliliter (ng/ml) units. Elevated PSA levels may indicate the presence of prostate cancer. However, PSA elevation may occur in a number of non-cancerous situations, as well, such as infection, prostatitis and benign prostatic enlargement (BPH). Therefore, urologist may use other tests associated with the PSA before recommending a prostate biopsy to diagnose prostate cancer.
Free PSA and Prostate Cancer
Some of the PSA in the blood stream is attached to other proteins; these are called "Bound PSA". The rest circulate freely, without being bound to other proteins. The freely circulating PSA is called "Free PSA". Total PSA is the amount of "Free PSA" plus "Bound PSA". Researchers have discovered an association between the percent of Free PSA in the blood stream and prostate cancer. The lower the amount of Free PSA, the higher is the chance for prostate cancer. In general, if the Free PSA is less than 25%, then a prostate biopsy is recommended.
How fast the PSA rises over time is also a risk factor for prostate cancer. A rate of 0.75 ng/ml or higher per year is associated with higher risk of cancer, prompting the need for biopsy.
The normal range for PSA is related to a person's age. In general, a PSA greater than 4.0 ng/ml is considered abnormal. However, age-based PSA can be used to fine-tune the need to proceed with a biopsy.