MSK PSA Doubling Calculator

PSA Doubling Time Formula:

\[ T_d = \frac{\ln(2) \times (t_2 - t_1)}{\ln(PSA_2 / PSA_1)} \]

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 prostate-specific antigen levels to double in the blood. It's an important prognostic marker in prostate cancer management, helping assess disease aggressiveness and guide treatment decisions.

2. How Does the Calculator Work?

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

\[ T_d = \frac{\ln(2) \times (t_2 - t_1)}{\ln(PSA_2 / PSA_1)} \]

Where:

\( T_d \) — PSA doubling time (months)
\( PSA_1 \) — Initial PSA value (ng/mL)
\( PSA_2 \) — Current PSA value (ng/mL)
\( t_1 \) — Time of initial PSA (months ago)
\( t_2 \) — Time of current PSA (months ago)
\( \ln \) — Natural logarithm function

Explanation: The formula calculates the time required for PSA to double based on the rate of change between two measurements.

3. Clinical Importance of PSA Doubling Time

Details: PSADT helps differentiate between aggressive and indolent prostate cancer. Shorter doubling times (<3 months) are associated with higher risk of progression and mortality, while longer times (>12 months) suggest less aggressive disease.

4. Using the Calculator

Tips: Enter PSA values in ng/mL and time points in months. Ensure PSA values are from the same assay method when possible, and that the time interval between measurements is sufficient (typically at least 3 months).

5. Frequently Asked Questions (FAQ)

Q1: How many PSA values are needed to calculate doubling time?
A: While two points can estimate doubling time, more measurements over time provide greater accuracy in clinical practice.

Q2: What is a concerning PSA doubling time?
A: Generally, <3 months is high risk, 3-9 months is intermediate risk, and >9-15 months is low risk for progression.

Q3: Does PSA doubling time apply after treatment?
A: Yes, PSADT after radical prostatectomy or radiation therapy remains prognostic for disease recurrence.

Q4: Are there limitations to PSADT calculation?
A: Accuracy decreases with very low PSA values (<0.5 ng/mL) or when PSA fluctuations are large relative to the absolute value.

Q5: How does PSADT affect treatment decisions?
A: Shorter PSADT may prompt earlier intervention in recurrent disease or consideration of more aggressive therapy in untreated patients.