Enter the time interval between the two PSA measurements and the second and first PSA measurements into the calculator to determine the PSA Doubling Time.

PSA Doubling Time Calculator

Enter any 3 values to calculate the missing variable

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PSA Doubling Time Formula

The following formula is used to calculate the PSA Doubling Time:

DT = (t * \ln(2)) / \ln(P2/P1)

Variables:

  • DT is the PSA Doubling Time
  • t is the time interval between the two PSA measurements
  • P2 is the second PSA measurement
  • P1 is the first PSA measurement

To calculate the PSA Doubling Time, multiply the time interval between the two PSA measurements by the natural logarithm of 2. Then divide the result by the natural logarithm of the ratio of the second PSA measurement to the first PSA measurement.

What is a PSA Doubling Time?

PSA Doubling Time refers to the period it takes for the level of Prostate-Specific Antigen (PSA) in a man's blood to double. PSA is a protein produced by both normal and malignant cells in the prostate gland. The PSA Doubling Time is often used as an indicator of the aggressiveness of prostate cancer and the effectiveness of treatment.

A short PSA Doubling Time (for example, less than about 3 months) is often associated with more aggressive disease and a poorer prognosis, while a longer PSA Doubling Time (for example, more than about 12 months) is often associated with less aggressive disease and a better prognosis. If PSA is decreasing (PSA2 < PSA1), the formula will yield a negative value; this indicates decline rather than growth (the absolute value can be interpreted as a “halving time”).

How to Calculate PSA Doubling Time?

The following steps outline how to calculate the PSA Doubling Time.

  1. First, determine the initial PSA level (PSA1).
  2. Next, determine the final PSA level (PSA2).
  3. Next, calculate the ratio of the final to initial PSA levels (PSA2 / PSA1).
  4. Finally, calculate PSA Doubling Time using DT = t × ln(2) / ln(PSA2/PSA1), where t is the time interval between the two measurements (DT will be in the same time units as t).
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Initial PSA level (PSA1) = 4.5

Final PSA level (PSA2) = 9.2

Time interval between the two PSA measurements = 6 months