The tests discussed below are used to look for warning signs of prostate cancer. But these early detection tests can’t tell for sure if a man has cancer. If the result of one of these tests is abnormal, you will probably need a prostate biopsy to determine if you have cancer. (A biopsy uses needles to take samples from the prostate and looking at the cells under a microscope.)
Prostate-Specific Antigen (PSA) Blood Test
What is a PSA?
Prostate-specific antigen (PSA) is a substance made by cells in the prostate gland (both normal cells and cancer cells). PSA is mostly found in semen, but 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 guarantee that a man doesn’t have cancer – about 15% of men with a PSA below 4 will have prostate cancer on a biopsy. Men with borderline PSA level 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%.
If your PSA level is high, your doctor may advise either waiting a while and repeating the test, or getting a prostate biopsy to find out if you have cancer (see the section, “What if the test results aren’t normal?”). Not all doctors use the same PSA cutoff point when advising whether to do a biopsy. Some may advise it if the PSA is 4 or higher, while others might recommend it at 2.5 or higher. Other factors, such as your age, race, and family history, may also come into play.
Factors that might affect PSA levels
The PSA level can also be increased by a number of factors other than prostate cancer, such as:
- An enlarged prostate:Conditions such as benign prostatic hyperplasia (BPH), a non-cancerous enlargement of the prostate that many men get as they grow older, may raise PSA levels.
- Older age:PSA levels normally go up slowly as you get older, even if you have no prostate abnormality.
- Prostatitis: This term refers to infection or inflammation of the prostate gland, which may raise PSA levels.
- Ejaculation: Thiscan cause the PSA to go up for a short time, and then go down again. This is why some doctors suggest that men abstain from ejaculation for 2 days before testing.
- Riding a bicycle: Some studies have suggested that cycling may raise PSA levels (possibly because the seat puts pressure on the prostate), although not all studies have found this.
- Certain urologic procedures:Some procedures done in a doctor’s office that affect the prostate, such as a prostate biopsy or cystoscopy, may result in higher PSA levels for a short time. Some studies have suggested that a digital rectal exam (DRE) might raise PSA levels slightly, although other studies have not found this. Still, if both a PSA test and a DRE are being done during a doctor visit, some doctors advise having the blood drawn for the PSA before having the DRE, just in case.
- Certain medicines: Taking testosterone (or other medicines that raise testosterone levels) may cause a rise in PSA.
Some things might cause PSA levels to go down (even if cancer is present):
- Certain medicines:Certain drugs used to treat BPH or urinary symptoms, such as finasteride (Proscar or Propecia) or dutasteride (Avodart), may lower PSA levels. 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.
- Herbal mixtures:Some mixtures that are sold as dietary supplements 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 affect PSA.
- Obesity:Obese (very overweight) men tend to have lower PSA levels.
- Aspirin:Some recent research has suggested that men taking aspirin regularly may have lower PSA levels. This effect may be greater in non-smokers. More research is needed to confirm this finding. If you take aspirin regularly (such as to help prevent heart disease), talk to your doctor before you stop taking it for any reason.
For men not known to have prostate cancer, it is not always clear if lowering the PSA is helpful. In some cases the factor that lowers the PSA may also lower a man’s risk of prostate cancer. But in other cases, it might lower the PSA level without affecting a man’s risk of cancer. This could actually be harmful, if it were to lower the PSA from an abnormal level to a normal one, as it might result in not detecting a cancer. This is why it is important to talk to your doctor about anything that might affect your PSA level.
Newer types of PSA tests
Some doctors might consider using newer types of PSA tests (discussed below) to help decide if you need a prostate biopsy, but 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
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 and helps some men 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, and the cutoff may change depending on PSA level.
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.
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. Some research has found that these levels go up faster if a man has cancer, but studies have not shown that the PSA velocity is more helpful than the PSA level itself in finding prostate cancer. For this reason, the ACS guideline does not recommend using the PSA velocity as part of screening for prostate cancer.
PSA levels are higher in men with larger prostate glands. The PSA density (PSAD) is sometimes used for men with large prostate glands to try to adjust for this. 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 indicates a greater likelihood of cancer. PSA density has not been shown to be as useful as the percent-free PSA test.
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.
Even if cancer cells are found, remember that all cancer cells are not the same. They can differ widely in their severity or aggressiveness. The pathologist will grade the cancer cells they find. They are measuring how much the cancerous prostate differs from normal prostate tissue. The pathologist assigns a grade to the most common tumor pattern, and a second grade to the next most common tumor pattern. The two grades are added together to get a Gleason Score. For example, if the most common tumor pattern was grade 3, and the next most common tumor pattern was grade 4, the Gleason Score would be 3+4 = 7. The Gleason Score ranges from 2 to 10, with 10 having the worst prognosis. For Gleason Score 7, a Gleason 4+3 is considered a more aggressive cancer than a Gleason 3+4.
The higher the grade, the more likely it is that the tumor will grow quickly and spread. Your doctor uses the tumor grade along with things like your age and overall health to decide how best to treat you.
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 just in front of the rectum, and most cancers begin in the back part of the gland, which can be felt during a rectal exam. This exam can be uncomfortable (especially in men who have hemorrhoids), but it usually isn’t painful and only takes a short time.
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.
Prostate ultrasound involves a probe about the size of a finger that is inserted a short distance into the rectum. This probe produces harmless high-frequency sound waves, inaudible to the human ear, that bounce off the surface of the prostate. The sound waves are recorded and transformed into video or photographic images of the prostate gland.
The probe can provide images at different angles to help your doctor estimate the size of your prostate and detect any abnormal growths.
A prostate biopsy uses trans-rectal ultrasound imaging to guide several small needles through the rectum wall into areas of the prostate where abnormalities are detected. The needles remove a tiny amount of tissue. Usually six or more biopsies are taken to test various areas of the prostate. The tissue samples are then analyzed in a laboratory. The results will help doctors diagnose disorders and diseases in the prostate. If cancer is identified, the doctor will be able to grade the cancer and determine its aggressiveness or likelihood of spreading.
Some doctors perform the biopsy through the perineum (skin between the scrotum and rectum).Researchers are investigating alternative biopsy procedures in efforts to maximize the accuracy of these results.
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. The ultrasound probe is about the width of a finger and is lubricated before it is placed in your rectum. 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. 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.