How effective is a PSA test for detecting prostate cancer?

An elevated prostate-specific antigen (PSA) score does not necessarily mean that you have prostate cancer. The PSA score may mean you have prostatitis or even a benign enlarged prostate.

Dr. Marc B. Garnick, MD
Hematologist & Oncologist

A prostate-specific antigen (PSA) test is a blood test that measures the level of a protein called prostate-specific antigen (PSA), which is made by cells in the prostate. Doctors use the test to detect prostate cancer, but it does not provide a definitive diagnosis.

The downside to testing is that an elevated PSA cannot differentiate aggressive tumors from slow-growing, harmless ones that might never cause symptoms during a man's life. Nor can it differentiate cancer from BPH or prostatitis. As a result, it can cause needless worry—and may lead to costly and invasive procedures, such as biopsies, to determine if cancer is present. Conversely, PSA screening doesn't detect all cancers, so a normal PSA level may offer a false sense of security. Many men with cancer confined to the prostate have normal PSA values. Even advocates of PSA testing doubt its value in men with less than a 10-year life expectancy (ages 75 or older, for men in average health) because these men are more likely to die of something else first.

Studies question the benefit of PSA screening—does it save lives by enabling doctors to treat aggressive prostate cancers early, or does it harm men who would never die from the disease by subjecting them to the side effects of treatment?

Even though PSA screening increased the diagnosis of prostate cancer, it did not improve the prostate cancer survival rate, and showed no real differences in the numbers of deaths from other causes.

In the United States, the lifetime risk of dying from prostate cancer is 3 percent. A 27 percent relative risk reduction would mean that, with screening, the risk of dying from prostate cancer would drop from 3 percent to 2.19 percent.

In Europe, that modest benefit came at a steep price. Researchers calculated that 48 men who are not at risk of dying from prostate cancer would have to be treated in order for screening to prevent one death from the disease over nine years. In other words, 48 men would risk the side effects of treatment to save one life.

Recent studies have cast serious doubts on the usefulness of PSA screening for all men. One conclusion that can be drawn from the studies: men should think carefully about PSA screening and discuss the risks and potential benefits with their doctors before having the test.

The prostate-specific antigen (PSA) test has received a lot of good and a lot of bad press. I always used to teach the medical students that there is PSA density, PSA velocity, PSA free and total complement PSA, and whenever there are four variations of a test, it means that it’s not a perfect test. So the PSA test is something that we use in combination with clinical judgment and a digital rectal examination. There’s no question that men with an elevated PSA are more likely to have prostate cancer. But you can have prostate cancer with a very low PSA and you can have an elevated PSA and not have prostate cancer. So although the PSA test is by far not a perfect test, it is still the best screening tool that we have to date.

The major challenge (for PSA testing), is to identify the cases that need to be treated while avoiding diagnosing patients who will not benefit from being diagnosed and who will only suffer from:

  • the stigma of being a cancer patient.
  • possible consequences/complications of overtreatment.

PSA (prostate-specific antigen) is a substance made by the prostate gland. Although PSA is mostly found in semen, a small amount is also found in the blood. Most healthy men have levels under 4 ng/mL (nanograms per milliliter) of blood. The chance of having prostate cancer goes up as the PSA level goes up. If your level is between 4 and 10, you have about a 1 in 4 chance of having prostate cancer. If it is above 10, your chance is over 50 percent, but some men with a PSA below 4 can also have prostate cancer.

Factors other than cancer can also cause the PSA level to go up, including:

  • An enlarged prostate like BPH (benign prostatic hyperplasia—not cancer), that many men get as they grow older.
  • Age: PSA levels go up slowly as you get older, even if you have no prostate changes.
  • 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.
  • Riding a bicycle.
  • Certain urology tests.

Some things can cause PSA levels to go down, even when cancer is present:

  • Certain medicines used to treat BPH or urinary symptoms. You should tell your doctor if you are taking medicines for these problems, because the doctor will need to adjust the reading.
  • Some herbal mixtures that are sold as dietary supplements may also hide 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 not meant for prostate health. Saw palmetto (an herb used by some men to treat BPH) does not seem to affect the measurement of PSA.
  • Obesity: Very overweight 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.

Although the prostate-specific antigen (PSA) test is not perfect, it is the best currently available test for early detection of prostate cancer. Since doctors started using the test, the number of prostate cancers found at an early, curable stage has increased. Because most men have normal test results, they can be reassured that they are unlikely to have prostate cancer, especially if the digital rectal exam (DRE) is also negative.

While the PSA test is considered a major advance in diagnosing early-stage prostate cancer, it has some drawbacks. For 100 men over 50 at average risk for prostate cancer, the following would be found if they all had a PSA test:

  • Ten of the 100 men would have a PSA level higher than normal (over 4.0). The 10 men would need further testing to clarify their abnormal levels.
  • Three of the 10 men would be found to have prostate cancer.
  • Seven of the 10 men would be found not to have prostate cancer. They would have an elevated PSA for other reasons—most likely benign prostatic hyperplasia (BPH).
  • Ninety of the 100 men would have PSA levels in the normal range (<4.0).
  • One or two of these 90 men would be found to have significant prostate cancer that becomes life threatening.

This shows that the PSA test is moderately sensitive. Of 100 men with prostate cancer, it will detect only about 70 of them, a sensitivity of about 70 percent. But the positive predictive value of the PSA test is low. Only three out of 10 positive results were cancer (PPV of about 30 percent). And seven out of 10 positive PSA results (i.e., greater than 4.0) are false-positive results; this means that two out of three men who are told that they may have cancer after taking the PSA test actually do not have it. When the PSA is greater than 10.0, the test is more accurate. There is about a 50-50 chance of having cancer at this level of PSA.

Negative predictive value is high reflecting the low likelihood of having significant prostate cancer with a normal PSA level (NPV of about 98 percent).

The prostate gland produces a protein called prostate-stimulating antigen, or PSA. Often, PSA levels will begin to rise before there are any symptoms of prostate cancer. Sometimes, an abnormal digital rectal exam may be the only sign of prostate cancer (even if the PSA is normal). If you have an elevated PSA, your doctor may have recommended a biopsy to tell if you have prostate cancer.

Dr. Mark S. Litwin, MD

Like many medical tests, the prostate-specific antigen (PSA) test for prostate cancer is not perfect. Prostate cancer can exist in the setting of a normal PSA, or you could have an elevated PSA in the absence of prostate cancer. It's an imperfect test, but a PSA test is often recommended by doctors who are looking for early indications of prostate cancer.

Prostate specific antigen (PSA) can help detect prostate cancer when it is elevated. The issue is that there are many non-cancerous causes of an elevated PSA as well, such as benign prostatic hyperplasia (BPH), and prostatitis. The controversy over using PSA alone is that not all patients with elevated PSA have prostate cancer. PSA has to be used in conjunction with clinical factors such as symptoms, patient and family history, and physical exam when used as an indicator for prostate cancer.

Researchers are developing new tests for prostate cancer, but they're expensive. In this video, Simon Hall, MD, a urologist at The Mount Sinai Medical Center, discusses the PSA.

An elevated PSA score (on a prostate specific antigen test) doesn't necessarily mean you have prostate cancer; a high score can also be associated with other conditions, like benign inflammation of the prostate. Only a biopsy can determine whether it's prostate cancer or not. You and your doc should agree on a course of action you will follow if you have an abnormal reading before you get the PSA test. It is the change from your baseline PSA value rather than the absolute number that interest the doctors; the trend can predict early cancer that most responds to treatment.

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Preventive Medicine Specialist

A truly specific test is one that only generates an abnormal result when the disease in question is present. Such a test is very useful at ruling disease in, because it will almost never be positive when disease is absent—and thus if positive, the test reliably rules in disease. Alas, the PSA is not such a test. The result of the test’s low specificity is that many men without prostate cancer wind up having unnecessary biopsies, and sometimes, complications of those biopsies.

The PSA might still be useful if it were highly sensitive. A highly sensitive test is reliably abnormal when disease is present. When a highly sensitive test result is normal, it is a very reliable indicator that disease is truly absent. But again, the PSA falls short. Levels in many cases of prostate cancer are not appreciably different from levels seen in normal men—and thus the test cannot be counted on to rule disease out either.

The PSA test has many false positive results for cancer, but also detects benign prostate hyperplasia (BPH) and prostatitis. If one of our patients has an elevated PSA, I treat them with antibiotics (after culture), which in many instances reduces the PSA to normal levels and avoids a biopsy. That treatment makes the diagnosis of prostatitis, and many of these patients urinate and feel better after the antibiotics.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.