What tests can detect prostate cancer?
The tests discussed below are used to look for warning signs of prostate cancer. But these early detection tests can’t tell for sure whether or not cancer is present. If the results of one or more of these tests are abnormal, you will likely need a prostate biopsy to determine if you have cancer. (A biopsy involves using needles to take samples from the prostate and looking at the cells under a microscope.)
Prostate-specific antigen (PSA) blood test
Prostate-specific antigen (PSA) is a substance made by cells in prostate gland (it is made by both normal cells and cancer cells). Although PSA is mostly found in semen, a small amount is also found in the blood. Most healthy men have levels under 4 nanograms per milliliter (ng/mL) of blood. The chance of having prostate cancer goes up as the PSA level goes up.
When prostate cancer develops, the PSA level usually goes above 4. Still, a level below 4 does not mean that cancer isn’t present — about 15% of men with a PSA below 4 will have prostate cancer on biopsy. Men with a PSA level in the borderline range between 4 and 10 have about a 1 in 4 chance of having prostate cancer. If the PSA is more than 10, the chance of having prostate cancer is over 50%.
The PSA level can also be increased by a number of factors other than prostate cancer, such as:
- An enlarged prostate, such as with benign prostatic hyperplasia (BPH), a non-cancerous enlargement of the prostate that many men get as they grow older.
- Age: PSA levels will also normally go up slowly as you get older, even if you have no prostate abnormality.
- Infection or inflammation of the prostate gland (prostatitis)
- Ejaculation can cause the PSA to go up for a short time, and then go down again. This is why some doctors will suggest that men abstain from ejaculation for 2 days before testing.
- Riding a bicycle
- Certain urologic procedures
Some things cause PSA levels to go down (even when cancer is present), including:
- Certain medicines used to treat BPH or urinary symptoms, such as finasteride (Proscar or Propecia) or dutasteride (Avodart). You should tell your doctor if you are taking these medicines because they may lower PSA levels and require the doctor to adjust the reading.
- Some herbal mixtures that are sold as dietary supplements “for prostate health” may also mask a high PSA level. This is why it is important to let your doctor know if you are taking any type of supplement, even ones that are not necessarily meant for prostate health. Saw palmetto (an herb used by some men to treat BPH) does not seem to interfere with the measurement of PSA.
- Some steroids may also change PSA levels
- Obesity: Obese (having a high amount of extra body fat) men tend to have lower PSA levels
- Aspirin: Men taking aspirin regularly tend to have lower PSA levels. This effect is most pronounced in non-smokers.
If your PSA level is high, your doctor may advise a prostate biopsy to find out if you have cancer. Some doctors may consider using newer types of PSA tests (discussed below) to help decide if you need a prostate biopsy. Still, not all doctors agree on how to use these other PSA tests. If your PSA test result is not normal, ask your doctor to discuss your cancer risk and your need for further tests.
Percent-free PSA
PSA occurs in 2 major forms in the blood. One form is attached to blood proteins while the other circulates free (unattached). The percent-free PSA (fPSA) is the ratio of how much PSA circulates free compared to the total PSA level. The percentage of free PSA is lower in men who have prostate cancer than in men who do not.
This test is sometimes used to help decide if you should have a prostate biopsy if your PSA results are in the borderline range (between 4 and 10). A lower percent-free PSA means that your likelihood of having prostate cancer is higher and you should probably have a biopsy. Many doctors recommend biopsies for men whose percent-free PSA is 10% or less, and advise that men consider a biopsy if it is between 10% and 25%. Using these cutoffs detects most cancers while helping some men to avoid unnecessary prostate biopsies. This test is widely used, but not all doctors agree that 25% is the best “cutoff point” to decide on a biopsy. Some doctors use a different cutoff for different PSA levels.
A newer test, known as complexed PSA, directly measures the amount of PSA that is attached to other proteins (the portion of PSA that is not “free”). This test is done instead of checking the total and free PSA, and it could give the same amount of information as the other two done separately. Studies are now under way to see if this test provides the same level of accuracy
PSA velocity
The PSA velocity is not a separate test. It is a measure of how fast the PSA rises over time. Normally, PSA levels go up slowly with age. Experts noticed that these levels can go up faster when cancer is present. When this issue was looked at further, though, studies showed that the PSA velocity was not more helpful than the PSA itself in finding prostate cancer. For this reason, the most recent ACS guideline on early detection of prostate cancer does not recommend using the PSA velocity.
PSA density
PSA levels are higher in men with larger prostate glands. The PSA density (PSAD) tries to adjust for this. It is sometimes used for men with large prostate glands. The doctor measures the volume (size) of the prostate gland with transrectal ultrasound (discussed below) and divides the PSA number by the prostate volume. A higher PSA density (PSAD) indicates greater likelihood of cancer. PSA density has not been shown to be that useful. The percent-free PSA test has so far been shown to be more helpful.
Age-specific PSA ranges
PSA levels are normally higher in older men than in younger men, even when there is no cancer. A PSA result within the borderline range might be very worrisome in a 50-year-old man but cause less concern in an 80-year-old man. For this reason, some doctors have suggested comparing PSA results with results from other men of the same age.
But because the usefulness of age-specific PSA ranges is not well proven, most doctors and professional organizations (as well as the makers of the PSA tests) do not recommend their use at this time.
Digital rectal exam (DRE)
For a digital rectal exam (DRE), the doctor inserts a gloved, lubricated finger into the rectum to feel for any bumps or hard areas on the prostate that might be cancer. As shown in the picture below, the prostate gland is located just in front of the rectum, and most cancers begin in the back part of the gland that can be reached by a rectal exam. This exam is uncomfortable, but it’s not painful and only takes a short time. It is more uncomfortable in men who have hemorrhoids.
DRE is less effective than the PSA blood test in finding prostate cancer, but it can sometimes find cancers in men with normal PSA levels. For this reason, it may be included as a part of prostate cancer screening.
Transrectal ultrasound (TRUS)
Transrectal ultrasound (TRUS) uses sound waves to make an image of the prostate on a video screen. For this test, a small probe that gives off sound waves is placed in the rectum. The sound waves enter the prostate and create echoes that are picked up by the probe. A computer turns the pattern of echoes into a black and white image of the prostate.
The procedure often takes less than 10 minutes and is done in a doctor’s office or outpatient clinic. You will feel some pressure when the TRUS probe is placed in your rectum, but it is usually not painful. The area may be numbed before the procedure.
TRUS is not used as a screening test for prostate cancer because it can’t always tell the difference between normal tissue and cancer. Instead, it is most often used during a prostate biopsy (described under “The prostate biopsy” in the section “What if the test results aren’t normal?”). TRUS is used to guide the biopsy needles into the right area of the prostate.
TRUS is useful in other situations as well. It can be used to measure the size of the prostate gland, which can help determine the PSA density and may also affect which treatment options a man has.