All Blood Tests

Prostate specific antigen (PSA) was discovered in 1979. It’s a protein made 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 usually the first line of tests done for detecting prostate cancer. If a suspicious locating occurs in either of these kinds of tests, your physician will probably order follow-up tests, like a percent-free PSA test or transrectal prostate ultrasound, to determine when you should have a prostate biopsy.

The PSA velocity test is a measurement of the sum PSA level over a period of time. Total PSA velocity should be determined over 24 months by measuring the sum PSA on at least three separate occasions, spaced as equally apart as possible — ideally, every 8 months. A rise in sum 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 sum 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 sum 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 primarily 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.

Follow-Up Testing

Once your doctor decides that you have an abnormal digital rectal investigation or an abnormal PSA (based on sum 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 physician 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 to definitively diagnose cancer.

Reliability

Total PSA Test

The sum level of PSA in serum is increased by factors other than cancer. Now, like the DRE, sum blood PSA alone is neither valid nor optimally specific for prostate cancer screening. Only 15 to 25 percent of men with an elevated sum PSA (greater than 4 ng/dL) are found to actually have prostate cancer. Similarly, up to 30 percent of men who do indeed have prostate cancer have a normal sum PSA blood level.

PSA Velocity Test

This kind of 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’s truly absent. Therefore, this test is pretty good at detecting prostate cancer when you truly have it, and it’s very good at informing you that you don’t have it. Nonetheless, since this test is done over a 2-year period, it isn’t appropriate when a quick diagnosis is necessary.

Health Risks

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 so of biopsy (if one is done) rather than so 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 usually cover these tests for men over 50.