Prostate-specific antigen (PSA) is a protein produced by both cancerous and noncancerous tissue in the prostate gland, a small gland located below the bladder in males. A standard PSA test measures the total amount of this protein in the blood at a single point in time. PSA velocity assesses the rate at which PSA levels change over a period, tracking trends that might indicate a developing prostate condition.
Calculating PSA Velocity
Calculating PSA velocity involves analyzing multiple PSA test results obtained over a specified timeframe. Healthcare providers typically require at least three separate PSA measurements taken over an 18 to 24-month period. For accurate results, all blood samples should ideally be processed by the same laboratory to reduce variations.
The calculation involves subtracting an earlier PSA level from a later one and dividing the difference by the time elapsed between measurements, expressed in nanograms per milliliter per year (ng/mL/year). For example, if a PSA level increased from 1.0 ng/mL to 2.5 ng/mL over two years, the PSA velocity would be (2.5 – 1.0) / 2 years, resulting in 0.75 ng/mL/year. This method offers a dynamic view of changes in prostate health.
Interpreting the Results
Historically, a rising PSA velocity was considered an indicator for clinicians to assess for prostate cancer. A rapid increase in PSA levels over time was thought to suggest a higher likelihood of aggressive prostate cancer compared to a slow, gradual rise. Specific thresholds were previously identified as concerning.
For instance, an increase of more than 0.75 ng/mL in a single year was once considered suspicious for cancer, particularly in men with baseline PSA levels below 10.0 ng/mL. A rise of 2.0 ng/mL within a year might indicate a more aggressive cancer type. While a rapid increase in PSA velocity was viewed as a potential warning sign, it was understood that it served as a risk indicator, not a definitive diagnosis of cancer. Further diagnostic steps, such as a prostate biopsy, were typically recommended to confirm suspicions.
Factors Influencing PSA Levels
Numerous non-cancerous conditions and activities can cause PSA levels to fluctuate, complicating the interpretation of PSA velocity. Benign Prostatic Hyperplasia (BPH), a non-cancerous enlargement of the prostate gland common in older men, can lead to increased PSA production. Prostatitis, an inflammation or infection of the prostate, also causes PSA levels to rise due to irritation and swelling.
Other factors that can temporarily increase PSA levels include:
- Normal aging, as prostate tissue naturally grows over time.
- Recent sexual activity, specifically ejaculation, for 24 to 72 hours.
- Certain medical procedures, such as a digital rectal exam (DRE) or a cystoscopy, due to direct prostate manipulation.
- Vigorous physical activities, including cycling or horseback riding.
Clinical Utility and Limitations
Despite its initial promise, the routine use of PSA velocity as a primary screening tool for prostate cancer has largely diminished in recent years. Major medical organizations, including the American Urological Association (AUA), no longer recommend its widespread use in general screening. This shift is largely due to studies indicating that PSA velocity does not consistently improve cancer detection accuracy when compared to a single PSA measurement or other predictive models.
One significant limitation of relying on PSA velocity is its high variability, meaning that PSA levels can fluctuate for many reasons unrelated to cancer. This variability can lead to false alarms, causing unnecessary anxiety for patients and potentially prompting unneeded prostate biopsies. While PSA velocity has fallen out of favor for general screening, a physician might still consider it as part of a more comprehensive assessment for individuals with existing risk factors, a family history of prostate cancer, or those already under active surveillance for a low-risk prostate cancer diagnosis.