Two hypothetical patients Considering the course of action with two hypothetical patients illustrates the difference between using a single PSA value vs. PSA velocity. Suppose a 55-year-old man just had a PSA test, with a result of 4.0. Under the current thinking, "the doctor looks and says, my gosh, we need to do a biopsy!” Carter says. If the patient's 10-year PSA history is available, however, the approach is much different. If it took the man 10 years for his PSA level to increase from 2 to 4, he has relatively little risk of an aggressive prostate cancer, so a biopsy may not be necessary, Carter says. But consider another hypothetical patient, also age 55, whose PSA level has climbed from 2 to 4 in the last five years. “That’s a whole different situation,” Carter says. “You'd want to do a biopsy, or monitor the patient closely." This scenario shows that "the current approach is a one-size-fits all, which isn't rational. Looking at a patient's PSA history is a much better way to evaluate their risk."

Calculating PSA velocity PSA velocity is the annualized rate of change in PSA reported as ng/ml (nanograms per milliliter) per year. An average rate of change is most accurate, and the formula is: { (PSA2 - PSA1/time) + (PSA3 - PSA2/time) } / 2 For example: Assume at time 0 the first PSA is 2.0ng/ml; then 14 months later it is 2.5; then 9 months after that it is 3.2ng/ml. To calculate PSA velocity:

• Take the difference between the first 2 measurements (0.5ng/ml) and then divide it by the time elapsed, to annualize it: 0.5ng/ml / 1.17 yrs = .43ng/ml per year.
• Then take the difference between the last 2 measurements (0.7ng/ml ) divided by the second time interval: 0.7ng/ml / 0.75 yrs = 0.93ng/ml per year.
• Then, add the 2 rates of change and divide by 2 to get an average rate of change: (0.43ng/ml/yr + 0.93ng/ml/yr) / 2 = 0.68ng/ml per year.

This patient's PSA velocity would be .68ng/ml per year. As this is significantly higher than the > .35 ng/mL per year threshold suggested by the latest research, the patient should have a biopsy, despite his PSA being less than 4.0.

RELATED LINKS

PSA screening guidelines from the American Urological Association Detection of Life-Threatening Prostate Cancer With Prostate-Specific Antigen Velocity During a Window of Curability (Journal of the National Cancer Institute, vol. 98, no. 21, Nov. 1, 2006) The Effectiveness of Screening for Prostate Cancer: A Nested Case-Control Study (Archives of Internal Medicine, vol. 166, no. 1, Jan. 9, 2006) Comparative Efficiency of Prostate-Specific Antigen Screening Strategies for Prostate Cancer Detection (Journal of the American Medical Association, vol. 284, no. 11, Sept. 20, 2000) PSA Screening Rates for Elderly Men Found Too High (ConsultantLive, Nov. 14) Have comments or questions on this article? Please e-mail the author, Sara Selis, at sselis@cmp.com.