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The prostate-specific antigen (PSA) test is a helpful measure in screening men for prostate cancer, a disease risk that increases considerably after age 50. At the same time, the test has limitations about which patients should be aware.

The PSA test does not specifically check for prostate cancer itself, but rather for the presence of a molecule in the blood naturally made by the prostate, said Dr. Christopher Saigal, vice chair of urology at the David Geffen School of Medicine at UCLA. Too much of the molecule in the blood can be a sign that the patient has prostate cancer.

Here are common factors that could change your PSA test results.

Common medications

Certain medications can alter the amount of the PSA molecule produced by the prostate – and thus the results of a PSA test. The drug finasteride, for example, is prescribed under the brand name Proscar to treat benign prostatic hyperplasia, a condition commonly known as an enlarged prostate. Finasteride is also prescribed under the brand name Propecia to treat male pattern baldness, the most prevalent form of hair loss in men.

Dr. Christopher Saigal, vice chair of urology at the David Geffen School of Medicine at UCLA

Saigal says that doctors administering a PSA test for patients taking finasteride will typically double the test results to achieve a comparable reading.

Certain infections

Having a urinary tract infection or inflammation of the prostate gland, known as prostatitis, can each greatly raise your PSA level. A urine test can easily diagnose a urinary tract infection so that it can be ruled out as a factor affecting the PSA test.

Sex and other physical activities

When a man ejaculates during sexual activity, PSA levels can be impacted, but only for up to 24 hours. The effect is minimal and would likely only change the person's PSA level by under a point on the test (one nanogram per milliliter). Saigal says doctors advise patients taking the test to abstain from ejaculation for 24 hours and to retest PSA levels if the test reading is borderline high.

Riding a bike for a long distance, which could put pressure on the prostate, has a similar effect on PSA levels.

It's important to remember that a PSA test alone isn't sufficient for a cancer diagnosis. Most men with an elevated PSA level – the equivalent of anywhere from 4 to 10 nanograms of PSA per milliliter of blood – don't have prostate cancer, Saigal says.

If any of these factors match your lifestyle, it's worth a conversation with your doctor as you prepare to take a PSA test.

Tags: cancer, cancer screening, Dr. Christopher Saigal, men's health, News & Insights, prostate, prostate cancer, prostate cancer screening prostatitis, prostate-specific antigen, prostatectomy, prostatic hyperplasia, PSA, PSA levels, psa test, urinary tract infection, urology, uti