What’s your PSA?
It’s a simple question, but for many men who choose to have the prostate-specific antigen blood test to screen for prostate cancer, there is no simple answer. That’s because PSA levels, like other biological functions, often vary. Since all prostate cells, both benign and malignant, produce the controversial protein, in most cases the swings have nothing to do with prostate cancer. And a new study sheds surprising light on a previously unsuspected reason for PSA variability.
Short-term variations in the PSA are well-known. Inflammation of the prostate (prostatitis) and urinary tract infections boost the PSA rapidly, often to very high levels. The same is true for medical manipulations that affect the gland, including prostate biopsies and the placement of a Foley catheter in the bladder. A doctor’s digital rectal exam (DRE) is a low-tech medical manipulation; some studies suggest that DREs can temporarily elevate blood PSA levels, while others do not.
A man’s behavior can also produce short-term changes in his PSA. For example, putting the prostate to work can nudge up PSA readings; when ejaculation elevates PSA results, the effect lasts less than 48 hours, which is why many doctors recommend a few days of abstinence before a blood sample is obtained for testing. Similarly, a vigorous workout on an exercise bike may produce a temporary PSA bump.
Technical factors may also explain short-term PSA variability. Even the best of labs may report different results when they test the same blood sample twice, but these differences are usually quite small. However, if different PSA testing methods are used by different labs, larger disparities can occur.
Long-term variation in PSA results is also common. The most important factor is age; over time, many men develop benign prostatic hyperplasia (BPH), and as the prostate enlarges, the PSA rises. Men who take finasteride (Proscar) or dutasteride (Avodart) to treat BPH typically experience about a 50% drop in their PSA values as their prostates shrink. In contrast, testosterone therapy can be expected to increase PSA levels as prostate cells enlarge.
In addition to change that can be traced to specific causes, changes in the PSA can develop without evident explanation. For example, a 2005 analysis of 12 earlier studies found that repeat PSA tests vary by about 20% in men older than 50. Similarly, a study of 972 men who each had five PSA tests during a four-year period revealed that a high proportion of men who had an abnormally high PSA result on one test had a normal PSA result on one or more subsequent test. In addition, a study of 295 men who had two PSA tests within 90 days found that consecutive results varied by more than 1.0 nanograms per milliliter (ng/mL) in one-third of the men.
When a man’s PSA reading seems to rise, the patient and his doctor should think about all the possible reasons for the change. And a report from Europe offers yet another possible explanation for varying PSA levels.
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