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PSA Tests For Prostate Cancer
Prostate specific antigen (PSA) was discovered in 1979. It is a protein produced by the cells that line the inside of the prostate. Prostate cancer changes the cellular barriers that normally keep PSA within the ductal system of the prostate, causing PSA to be released into the blood in higher quantities. All of the tests below consist of a simple blood draw and a laboratory analysis.
The total PSA test measures the total amount of PSA in your blood. The results are given in ng/ml (nanograms of PSA per milliliter blood), and a total PSA of 4 ng/ml or higher is considered to be a possible sign of prostate cancer. The risk increases as this number goes higher.
The total PSA and DRE (digital rectal examination) are generally the first line of tests done for detecting prostate cancer. If a suspicious finding occurs in either of these tests, your doctor will probably order follow-up tests, like a percent-free PSA test or transrectal prostate ultrasound, to determine if you should have a prostate biopsy.
The PSA velocity test is a measurement of the total PSA level over a period of time. Total PSA velocity should be determined over 24 months by measuring the total PSA on at least three separate occasions, spaced as equally apart as possible -- ideally, every 8 months. A rise in total PSA of over 0.75 ng/ml per year over this time is suggestive of prostate cancer and may warrant having a prostate biopsy.
The total PSA that is measured in the blood exists in two major forms -- PSA that circulates bound to proteins (the more abundant form) and PSA that circulates "free" in the blood (not bound to proteins). The percent-free PSA test, by measuring only that amount of the total PSA that is in the free form, enhances the overall reliability of the PSA test, because men with prostate cancer tend to have a lower percentage of PSA in the free form than men without prostate cancer.
The percent-free PSA test is mainly used as a follow-up test in men who are found to have a total PSA level in the so-called "gray area" -- between 4 ng/ml and 9.9 ng/ml -- to help determine who should undergo a prostate biopsy and who should not. Currently, a prostate biopsy is recommended in these men when their percent-free PSA is less than 10 percent. A biopsy is usually not recommended when their percent-free PSA is greater than 25 percent. If the percent-free PSA is between 10 and 25 percent, the patient's overall risk profile is used to decide how to proceed.
Once your doctor determines that you have an abnormal digital rectal examination or an abnormal PSA (based on total levels, percent-free PSA, PSA velocity, or a combination), the next step will most likely be a transrectal ultrasound of your prostate.
For the transrectal prostate ultrasound (TPU), a cylinder-shaped ultrasound probe will be gently placed in your rectum as you lie on your left side with your knees bent. The probe is rocked back and forth to obtain images of the entire prostate. The procedure takes about 15 to 25 minutes to perform.
The TPU can display both the smooth-surfaced outer shell of the prostate and the core tissues surrounding the urethra (the tube that comes out of the bladder down through the penis). The doctor will look at the entire volume of your prostate.
If the TPU shows an enlarged prostate, this indicates either inflammation of the prostate (prostatitis) or benign enlargement of the gland. A TPU showing either a distinct lump or an irregular area within the gland suggests cancer. If a lump or irregularity is seen, a biopsy will be taken in order to definitively diagnose cancer.
Total PSA Test
The total level of PSA in serum is increased by factors other than cancer. So, like the DRE, total blood PSA alone is neither accurate nor optimally specific for prostate cancer screening. Only 15 to 25 percent of men with an elevated total PSA (greater than 4 ng/dL) are found to actually have prostate cancer. Similarly, up to 30 percent of men who do in fact have prostate cancer have a normal total PSA blood level.
PSA Velocity Test
This test has a reported sensitivity of about 72 percent and a specificity of 95 percent. Remember, sensitivity is the ability to detect the disease when it's truly there. Specificity is the ability to detect the absence of disease when it is truly absent. Therefore, this test is pretty good at detecting prostate cancer when you in fact have it, and it is very good at informing you that you do not have it. However, since this test is done over a 2-year period, it isn't appropriate when a quick diagnosis is necessary.
There are none for the various PSA tests; these are simple needle draws. And there are no serious risks from a TPU without a biopsy. Infection is rare, only occurring as a result of biopsy (if one is done) rather than as a result of the ultrasound itself.
Cost of the Screening Tests
The standard PSA blood test costs between $20 and $60. Some self-testing home kits are available for about $40 from Web sites like TestCountrycom. The free PSA blood test and the PSA velocity test cost about $100 each. Medicare and most health insurers typically cover these tests for men over 50.
Reprinted from: Medical Tests That Can Save Your Life: 21 Tests Your Doctor Won't Order ...Unless You Know to Ask by David Johnson, Ph.D., and David Sandmire, M.D. with Daniel Klein © 2004 by David Johnson, Ph.D. and David Sandmire, M.D. Permission granted by Rodale, Inc., Emmaus, PA 18098. Available wherever books are sold.