- For a 2-point PSADT: enter PSA1, PSA2, and the interval in months between them. Result updates automatically.
- For a multi-point PSADT (≥ 3 values): enter PSA values and their corresponding time from baseline (months) in any 3–5 of the rows. The calculator uses least-squares regression on ln(PSA) vs time.
- PSA values must be consistently measured in ng/mL by the same assay.
- PSADT is only valid when PSA is consistently rising — benign causes (prostatitis, BPH, biopsy) can falsely shorten the result.
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Formula
PSA doubling time (PSADT) measures how fast the PSA is rising, indicating the aggressiveness of prostate cancer recurrence or progression.
2-Point Formula
PSADT = (ln 2 × Δt) / ln(PSA2 / PSA1)
Where PSA1 = first value (ng/mL), PSA2 = second value (ng/mL), Δt = interval in months, ln = natural logarithm.
Multi-point Formula (≥ 3 data points)
Least-squares linear regression on ln(PSA) vs time (months). The slope of the regression line represents the PSA growth rate, and PSADT = ln(2) / slope. This method is more reliable than the 2-point method as it averages out measurement variability.
When to Use
Use PSADT whenever serial PSA measurements are available and a rising trend has been established.
Appropriate indications
- Biochemical recurrence after prostatectomy or radiation (rising PSA after nadir)
- Active surveillance monitoring — rising PSADT may trigger repeat biopsy or escalation of care
- Metastatic castration-resistant prostate cancer (CRPC) — PSADT correlates with overall survival
- CKD patients on hormonal therapy — renal impairment does not affect PSA or PSADT interpretation
When NOT to rely on it
PSADT requires a consistently rising PSA trend. Do not calculate if PSA has been stable, declining, or fluctuating due to benign causes (prostatitis, BPH flare, recent biopsy, ejaculation). A single elevated PSA is insufficient — at least 2 values are required; ≥ 3 values improve reliability.
Pearls & Pitfalls
Clinical pearls
- Short PSADT (< 3 months) after radical prostatectomy independently predicts metastasis and prostate cancer–specific mortality (Pound et al., JAMA 1999)
- Long PSADT (> 12 months) suggests slow progression; close monitoring with PSA every 3–6 months may be appropriate
- PSADT is a key independent predictor of metastasis and cancer-specific mortality in biochemical recurrence
- The multi-point method (≥ 3 values) is more reliable than the 2-point method — it averages out assay variation
Common pitfalls
- Benign causes of PSA rise (prostatitis, BPH, biopsy, sexual activity within 24–48 h) can falsely shorten PSADT — always use serial values with consistent pre-test conditions
- PSA units must be consistent (ng/mL throughout); mixing assays or labs introduces error
- PSADT is only valid when PSA is consistently rising — if PSA2 ≤ PSA1, no doubling time can be calculated
- In patients on 5-alpha reductase inhibitors, PSA values are suppressed ~50%; adjust or use unadjusted values from the same treatment period
Why Use It
PSADT is a key independent predictor of metastasis and cancer-specific mortality in biochemical recurrence. It guides timing of salvage therapy, ADT initiation, and enrollment in clinical trials. Unlike the raw PSA level, PSADT captures the velocity of disease progression — a PSA of 2.0 ng/mL doubling in 2 months is far more worrying than a PSA of 20 ng/mL that has been stable for years.
For nephrologists, PSADT is relevant in patients with CKD who develop biochemical recurrence while on ADT or novel hormonal agents, as renal impairment does not alter PSA kinetics but does affect drug dosing and monitoring decisions.
PSA Doubling Time Calculator
Use Section A for a quick 2-point calculation or Section B for a more reliable multi-point regression using 3–5 serial PSA values.
Section A — 2-Point PSADT
⚕ Formula: PSADT = (ln 2 × Δt) / ln(PSA2 / PSA1). Both values must be consistently rising and measured in ng/mL.
Section B — Multi-Point PSADT (≥ 3 Values, Least-Squares Regression)
Enter PSA values and time from baseline (months) for at least 3 measurement points. Leave unused rows blank.
⚕ Method: least-squares linear regression on ln(PSA) vs time (months). PSADT = ln(2) / slope. More reliable than 2-point method for ≥ 3 serial measurements.
Next Steps
Use PSADT to guide urgency of specialist referral and treatment escalation.
- PSADT < 3 months: high-risk rapid progression — urology/oncology consult urgent; consider ADT + novel AR pathway inhibitors (enzalutamide, abiraterone, darolutamide); PSMA PET imaging to detect metastatic disease.
- PSADT 3–6 months: rapid progression — early intervention discussion warranted; imaging (PSMA PET if available); salvage therapy discussion with radiation oncology or urology.
- PSADT 6–12 months: intermediate velocity — imaging and salvage therapy discussion; closely follow every 3 months.
- PSADT > 12 months: slow progression velocity — close monitoring with serial PSA every 3–6 months; may defer immediate systemic therapy in shared decision-making with patient.
- Apply PSADT in context of time to PSA rise after definitive therapy, PSA nadir, and Gleason grade group at diagnosis. Document PSADT trajectory in the oncology record at each visit.
Evidence & References
PSADT Risk Stratification
| PSADT | Risk Category | Clinical Implication |
|---|---|---|
| < 3 months | Very high / rapid | High risk of metastasis; urgent oncology consult; consider ADT + novel AR inhibitors |
| 3–6 months | High | Early intervention warranted; imaging; salvage therapy discussion |
| 6–12 months | Intermediate | Close monitoring every 3 months; imaging discussion |
| > 12 months | Low / slow | Serial PSA monitoring every 3–6 months; defer systemic therapy in shared decision |
References
- Pound CR, Partin AW, Eisenberger MA, Chan DW, Pearson JD, Walsh PC. Natural history of progression after PSA elevation following radical prostatectomy. JAMA. 1999;281(17):1591–1597.
- D'Amico AV, Moul J, Carroll PR, Sun L, Lubeck D, Chen MH. Cancer-specific mortality after surgery or radiation for patients with clinically localized prostate cancer managed during the prostate-specific antigen era. J Clin Oncol. 2003;21(11):2163–2172.
- American Urological Association. Prostate Cancer — Biochemical Recurrence After Definitive Local Therapy. AUA Guideline. 2023.
- Freedland SJ, Humphreys EB, Mangold LA, et al. Risk of prostate cancer–specific mortality following biochemical recurrence after radical prostatectomy. JAMA. 2005;294(4):433–439.
