Is My PSA Level Normal?
The absolute value of PSA has been the long-term standard of care to determine whether one’s PSA elevation is significant. Previously, the magic number of “4” was defined as being the upper limit of “normal.” However, this may not be a good rule of thumb since approximately 15% of prostate cancers can occur in men with a “normal” PSA.
When interpreting a PSA value, several factors need to be taken into consideration—not just the absolute value of the PSA. Some of these factors include:
- Age adjustment of the PSA
- PSA density
- Percent free PSA
- PSA velocity
Age-Adjusted PSA
Recent data has redefined the way that urologists look at PSA, and what is considered a "normal" PSA. Age-adjusted PSA values take into account that a 40-year-old should not have the same PSA as an 80-year-old. Accepted age-adjusted PSA rates are below 2.4 ng/ml for men under the age of 50 and 6.5 ng/ml for patients in their 70s. Other limits have been defined for varying age ranges, but there is not universal agreement about the accuracy of the age-adjusted levels.
Many times urologists are faced with the dilemma of the young patient with the elevated PSA. This is a difficult situation, since the patient often does not want to undergo a prostate biopsy that would help determine the significance of the PSA elevation, and does not want to be diagnosed with prostate cancer due to the potential side effects of prostate cancer treatment, which may include urinary incontinence and erectile dysfunction. In many cases, despite evidence that is not overwhelming in the urologic literature, patients are given a course of antibiotics with the assumption that this elevation is due to a prostatic infection. After completing a round of antibiotics, another PSA test is performed. If it remains elevated, a biopsy would usually be advised.
PSA Velocity
Patients often present with a rising PSA. The PSA velocity is defined as the rate of change of the PSA over a period time. For patients whose PSA is less than 2, a velocity of greater than 0.35 ng/mL per year is cause for concern. Patients with a PSA of 4-10 have reasons for concern when the PSA velocity is greater than 0.75 ng/ml. So while a rise in PSA from 1 to 1.5 may be a cause for concern, a rise from 5 to 5.5 may not.
An isolated rise of the PSA, (even if the rise exceeds the “safe” velocities) may not always be reason for alarm, but most agree that three successive PSA determinations over an 18-month period represents a meaningful velocity. PSA velocity is a useful tool for the urologist to look at when a patient shows a rising PSA, whether they have never had a prostate biopsy before, or when they had a biopsy that came back.
PSA Density
PSA density is defined as the PSA divided by the prostate volume. When comparing two patients who have the same elevated PSA and different prostate volumes, the patient who has the smaller prostate is more likely to have prostate cancer. The higher the PSA density, the more likely the patient is to have prostate cancer.
Percent Free PSA (PSA-f)
The percent free PSA (PSA-f) refers to the proportion of “free PSA” to “bound PSA” in the total PSA in the blood sample. The free PSA circulates in the bloodstream not attached to a carrier protein. The higher the percentage of free PSA, the lower the risk of cancer. For instance, a free PSA of 0-10% is associated with a 56% chance of cancer while a free PSA greater than 25% is only associated with an 8% risk of cancer.
