PSA Doubling Time Calculator

Why doubling time matters after prostate cancer treatment

After surgery or radiotherapy for prostate cancer, PSA is the marker followed at every check-up. A rise, called biochemical recurrence, does not by itself mean cancer has spread: after prostatectomy it is defined as a PSA of 0.2 ng/mL or more, confirmed by a second reading; after radiotherapy as a rise of 2 ng/mL above the lowest value reached.

How fast PSA rises says more than the level alone. Doubling time, the number of months it takes PSA to double, separates slow biological change from disease that needs prompt attention, and European Association of Urology guidelines use it when deciding on imaging and treatment.

How it is calculated, and why more results help

The calculation fits a straight line through the natural logarithm of each PSA value against time and divides ln 2 (about 0.693) by the slope. Two points define a line exactly, so any error in either result goes straight into the doubling time. Three or more results spread over at least three months average out the noise, which is why specialists prefer to wait for another reading before acting on a single rise.

Use results from the same laboratory: different assays can differ by 10 to 20 percent, enough to create or hide a trend at low values.

What short and long doubling times suggest

In a landmark study of men whose PSA rose after prostatectomy (Pound and colleagues, 1999), those with a doubling time under 10 months developed metastases much sooner than those with longer doubling times, and many men with slow doubling times lived for years without treatment. Later work and current guidelines treat a doubling time under 3 to 6 months as high risk, 6 to 12 months as intermediate and over 12 months as low risk, alongside the original tumour grade and how soon after treatment the rise began.

These are associations across groups of men, not predictions for one person. A short doubling time prompts imaging, increasingly with PSMA PET scans, and a conversation about salvage treatment or hormone therapy; a long one often supports continued monitoring.

Things that distort the number

• Values below 0.1 ng/mL: ultrasensitive assays fluctuate at this level and small absolute changes give alarming doubling times.
• PSA bounce: one to three years after radiotherapy or brachytherapy, PSA can rise temporarily and then fall again without any recurrence.
• Hormone therapy: androgen deprivation suppresses PSA production, so doubling time is not meaningful while on treatment or in the months after stopping it.
• Prostate infection or recent instrumentation can raise PSA briefly in men whose prostate is still in place.
• Changing laboratories between measurements.

What usually happens next

A confirmed rise leads to a conversation, not an automatic treatment. Depending on the doubling time, your original pathology, your age and health, and what imaging shows, the options range from continued PSA monitoring, through salvage radiotherapy or surgery, to hormone therapy, alone or with newer drugs. Guidelines increasingly recommend PSMA PET imaging before deciding, because it can locate small recurrences that older scans miss.

Ask for the reasoning behind each option, and for time to think. The decision is shared, and a second opinion is a normal part of prostate cancer care.

Questions to ask your specialist

Bring the result with you and ask:

• What is my PSA doubling time, and what threshold would change your advice?
• Do we have enough readings, or should we repeat the test first?
• Would a PSMA PET scan help, and is it available to me?
• What are the options if the rise continues, and what are the trade-offs of each?
• How does my original tumour grade affect the interpretation?