π PSA Doubling Time Calculator
How fast is the PSA moving? The kinetics that matter.
For informational purposes only, not medical advice. Consult a healthcare professional.
PSA doubling time asks how long the PSA would take to double at its current trajectory, and it is one of the most decision-relevant numbers in prostate cancer surveillance. After treatment, a short doubling time pushes toward earlier imaging and therapy; on active surveillance, it is a progression trigger. Urologists often quote under 3 years as concerning in surveillance contexts and under 6 to 12 months as high-risk after treatment. This calculator derives doubling time and velocity from two readings for discussion with your urologist.
How to Use This Calculator
Enter two PSA values with the days between the blood draws. The calculator gives doubling time in months and the annualized velocity.
Use two readings from the same lab, at least a few months apart. Short intervals amplify noise into scary-looking kinetics.
Enter the days between the draws exactly. The math annualizes from this interval, so guessing it corrupts the answer.
Read doubling time and velocity together. Fast doubling with low absolute values means something different from fast doubling at high values.
How the Math Works
Doubling time equals the natural log of 2 times the days between readings, divided by the natural log of the second PSA over the first. With PSA rising from 2.0 to 3.0 over 365 days, that is 0.693 times 365 divided by ln(1.5), about 625 days or 20.5 months. PSA velocity is the annualized rise: 1.0 ng/mL over the year. The exponential model assumes steady growth; real PSA bounces with infection and lab variation, which is why two points are the minimum and three or more are better. If the second value is lower, the calculator reports a halving time instead.
Worked Example
PSA rising from 2.0 to 3.0 ng/mL over a year gives a doubling time of 20.5 months and a velocity of 1.00 ng/mL/yr per year. The calculator places this in the Intermediate band: not the rapid kinetics that alarm, but not flat either. On active surveillance this pace typically means continued monitoring with the doubling time recalculated at each visit rather than an immediate trigger.
Reading Your Result
Doubling times over 3 years are generally reassuring kinetics. One to 3 years deserves attention and often shortens surveillance intervals. Under 1 year is rapid and usually prompts restaging or treatment discussion, especially after definitive therapy. Velocity above 0.75 to 2 ng/mL per year has been studied as an additional risk signal, though thresholds vary. Context rules: the same kinetics mean different things before diagnosis, on surveillance, and after treatment.
| Doubling time | Band | Typical reading |
|---|---|---|
| Over 36 months | Slow | Reassuring kinetics |
| 12-36 months | Intermediate | Closer surveillance |
| Under 12 months | Rapid | Restage / discuss treatment |
Limitations
Two points make a line but not a truth: prostatitis, instrumentation, ejaculation, and lab variation all distort single readings. The exponential model breaks down with bouncing values, and very low PSAs produce wild doubling times from tiny absolute changes. Kinetics never diagnose; they prioritize. Every decision here belongs with the urologist holding the full record.
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For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is PSA doubling time?
How long the PSA would take to double if it kept rising at its current exponential pace. Shorter doubling times mean faster-growing PSA production, which correlates with more aggressive disease behavior. It is a kinetics measure, not a level.
What doubling time is concerning?
Context-dependent. On active surveillance, under 3 years often triggers reevaluation; after prostatectomy or radiation, under 6 to 12 months is high-risk and under 3 months very high-risk. Your urologist calibrates the number to your situation.
What is PSA velocity?
The absolute rise per year in ng/mL. A velocity above roughly 0.75 to 2 per year has been associated with higher risk in studies, though the exact threshold is debated. Velocity and doubling time describe the same motion in different units.
Can PSA doubling time be calculated from two readings?
Yes, mathematically, but two points are the bare minimum and noise-prone. Three or more readings over a year give a far more trustworthy trend. One odd reading should be repeated before it drives decisions.
Why did my PSA drop? Does that break the math?
PSA falls with prostatitis resolving, after stopping confounders, or with 5-alpha-reductase inhibitors. The calculator then reports a halving time, which is informative in its own way. Falling PSA is generally reassuring but the reason matters.
Does a fast doubling time mean I have cancer?
No. Benign growth and prostatitis also raise PSA, sometimes quickly. Doubling time stratifies risk and urgency; it does not diagnose. Many men with brisk PSA rises turn out to have benign causes on workup.
How soon after treatment is doubling time used?
After prostatectomy, PSA should fall to undetectable; any confirmed rise triggers doubling-time math from the low values. After radiation, PSA falls slowly over years and the Phoenix definition (nadir plus 2) defines recurrence before kinetics take over.
Can lifestyle change PSA kinetics?
No intervention reliably slows PSA doubling except effective cancer treatment. Diet and supplements have not shown convincing effects on kinetics in trials. Do not delay proven evaluation chasing unproven modifiers.
What is PSA nadir?
The lowest PSA reached after treatment. After surgery it should be undetectable; after radiation it settles over 2 to 3 years. The nadir anchors all future kinetics: rises are measured from there.
Should I track this myself between visits?
Tracking helps you arrive informed, but resist acting on one new number. Bring the trend to the appointment and let the urologist interpret it with exams, imaging, and history. The calculator is a preparation tool, not a decision-maker.