Free PSA (%free PSA)
A refinement of the PSA test. PSA circulates in two forms — bound to proteins and 'free'. The percentage that is free helps tell apart a raised PSA caused by a benign enlarged prostate from one caused by cancer: a higher %free leans benign, a lower %free raises the chance of cancer.
What it measures
Prostate-specific antigen (PSA) travels in the blood in two forms: most is bound to proteins, and a smaller portion circulates 'free'. The free PSA test reports what proportion of the total PSA is free, expressed as a percentage. Its value is in refining a borderline total PSA — typically in the grey zone where PSA is mildly raised but not clearly high. The key observation is that prostate cancer tends to produce relatively less free PSA, so a low percentage of free PSA raises the probability that a raised total PSA is due to cancer, while a high percentage of free PSA leans toward a benign cause such as an enlarged prostate (BPH). It does not diagnose anything by itself: it is one input, alongside total PSA, examination, age and other factors, that helps a doctor and patient decide whether a prostate biopsy or further tests such as MRI are worthwhile — or whether monitoring is reasonable. Because many things move PSA (recent ejaculation, cycling, a urine infection, prostate procedures), free PSA is always interpreted in that context by a specialist.
What a high value can mean
- A higher %free PSA leans toward a benign cause — such as an enlarged prostate (BPH); it lowers, though does not remove, the probability of cancer.
- Used to reassure and avoid unnecessary biopsy — when the total PSA is only borderline.
What a low value can mean
- A lower %free PSA raises the probability of prostate cancer — in the context of a borderline total PSA; a reason to consider MRI or biopsy.
- It is a probability shift, not a diagnosis — many men with a low %free do not have cancer.
When to discuss with a doctor
Free PSA is a second-line, specialist test, used to make sense of a borderline total PSA rather than as a screen on its own. When PSA sits in the grey zone, the percentage of free PSA helps weigh up the chance of cancer versus a benign enlarged prostate, and feeds into a shared decision about whether an MRI or biopsy is worthwhile — a decision that also considers age, examination, family history and how the PSA is trending. A low %free is a reason to take a raised PSA more seriously, not a diagnosis. Because prostate care is nuanced and over-investigation carries its own harms, this belongs with a urologist. Mediora.AI shows free PSA alongside total PSA so the pattern is visible in one place; interpreting it and deciding on next steps belongs with your specialist.