Calculate PSA Doubling Time

PSA Doubling Time Formula:

\[ td = \frac{\ln(2)}{\frac{\ln(PSA2 / PSA1)}{(t2 - t1)}} \]

Initial PSA (PSA1):

ng/mL

Current PSA (PSA2):

ng/mL

Initial PSA Date (t1):

months ago

Current PSA Date (t2):

months ago

PSA Doubling Time (td):

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1. What is PSA Doubling Time?

PSA doubling time (PSADT) is the time it takes for the prostate-specific antigen (PSA) level to double in value. It's an important prognostic marker in prostate cancer management, helping assess disease aggressiveness and progression.

2. How Does the Calculator Work?

The calculator uses the following formula:

\[ td = \frac{\ln(2)}{\frac{\ln(PSA2 / PSA1)}{(t2 - t1)}} \]

Where:

\( td \) — PSA doubling time (months)
\( PSA1 \) — Initial PSA value (ng/mL)
\( PSA2 \) — Current PSA value (ng/mL)
\( t1 \) — Time of initial PSA (months ago)
\( t2 \) — Time of current PSA (months ago)
\( \ln \) — Natural logarithm

Explanation: The formula calculates the exponential growth rate of PSA and determines how long it would take to double at that rate.

3. Clinical Significance

Details: PSADT helps in:

Assessing prostate cancer aggressiveness
Predicting risk of recurrence after treatment
Guiding decisions about active surveillance vs. treatment
Evaluating response to therapy

4. Using the Calculator

Tips:

Enter PSA values in ng/mL
Enter time points as months ago (e.g., 0 for current, 6 for six months ago)
Ensure PSA values are from the same laboratory when possible
Use at least 3 PSA values over 6-12 months for most accurate calculation

5. Frequently Asked Questions (FAQ)

Q1: What is a concerning PSA doubling time?
A: Generally, PSADT < 3 months indicates aggressive disease, while >15 months suggests indolent disease.

Q2: How many PSA values are needed for accurate calculation?
A: While two points can calculate PSADT, using 3+ values over time provides more reliable results.

Q3: Does PSA doubling time differ after treatment?
A: Yes, PSADT after treatment (especially radiation) may have different prognostic significance than pre-treatment PSADT.

Q4: Can PSADT be used for active surveillance decisions?
A: Yes, PSADT is one factor considered in active surveillance protocols, often combined with other clinical factors.

Q5: What affects PSA doubling time accuracy?
A: Factors include PSA assay variability, prostate manipulation (biopsy, DRE), urinary tract infection, and medications.