MSK PSA Doubling Time Calculator

MSK PSA Doubling Time Formula:

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

Initial PSA (PSA1):

ng/mL

Current PSA (PSA2):

ng/mL

Initial Time (t1):

months

Current Time (t2):

months

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, particularly for monitoring disease progression and treatment response.

2. How Does the Calculator Work?

The calculator uses the Memorial Sloan Kettering (MSK) formula:

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

Where:

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

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

3. Clinical Importance of PSA Doubling Time

Details: PSADT is used to assess prostate cancer aggressiveness. Shorter doubling times (<3-6 months) may indicate more aggressive disease and influence treatment decisions.

4. Using the Calculator

Tips: Enter PSA values in ng/mL and time points in months. Ensure PSA2 > PSA1 and t2 > t1 for valid calculation. Use consistent units for all measurements.

5. Frequently Asked Questions (FAQ)

Q1: What is a clinically significant PSADT?
A: Generally, <3 months is concerning, 3-12 months may indicate intermediate risk, and >12 months suggests less aggressive disease.

Q2: How many PSA points are needed for accurate calculation?
A: While two points give an estimate, more measurements over time provide more reliable doubling time calculations.

Q3: Does PSADT apply to all prostate cancer patients?
A: It's most useful for monitoring after primary treatment (surgery/radiation) or in active surveillance cases.

Q4: What factors can affect PSADT accuracy?
A: PSA bounces after radiation, urinary infections, recent procedures, or certain medications can temporarily affect PSA levels.

Q5: How often should PSADT be recalculated?
A: Regular monitoring (e.g., every 3-6 months) with new PSA values provides ongoing assessment of disease progression.