Man and GP reviewing PSA test results

Free PSA vs Total PSA: What the Ratio Tells You

Total PSA is the whole amount of prostate-specific antigen in your blood. Free PSA is just the part that travels on its own, not attached to other proteins. Divide free by total and you get the percent free PSA, a number doctors sometimes use when a total PSA result lands in a grey area.

If you’ve got a result in front of you and the jargon is making your eyes glaze over, you’re in the right place. We’ll go through what each number means, how the ratio is worked out, what a low or high percentage can suggest, and where its limits are. No clinical fog, promise.

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TL;DR

  • Total PSA counts all the PSA in your blood, both bound to proteins and free. It’s the standard first test.
  • Free PSA is the unbound fraction. Divided by total PSA and multiplied by 100, it gives your percent free PSA.
  • A lower percentage is linked with a higher chance of prostate cancer, and a higher percentage more often points to a benign enlargement (BPH).
  • The ratio is mostly used when total PSA is in the 4 to 10 ng/mL range. It can’t diagnose or rule out cancer on its own.
  • Whatever your result, talk it through with a GP. They’ll look at your age, symptoms and history alongside the numbers.

Table of Contents

What PSA actually is

PSA stands for prostate-specific antigen. It’s a protein made by normal prostate cells and by prostate cancer cells, as Prostate Cancer UK explains. Having a little PSA in your blood is completely normal. Levels also creep up slightly with age as the prostate gets bigger.

So a PSA number isn’t a cancer number. It’s a prostate number. Plenty of things besides cancer can nudge it up, and that’s exactly why a second look at the figure, like the free-to-total ratio, can be handy.

Free PSA vs total PSA: the difference

PSA circulates in your blood in two forms. Some of it is attached to other proteins (the bound form). The rest floats around unattached (the free form). The Canadian Cancer Society sums it up like this: total PSA measures free and bound PSA together, while free PSA is only the unattached fraction.

Here’s a simple way to picture it:

Total PSA Free PSA
What it measures Bound plus free PSA Only the unbound PSA
Usually reported as ng/mL (sometimes µg/L, the same amount) ng/mL, or as a percentage of total
Role First-line PSA test Follow-up detail in a grey-zone result
Can diagnose cancer? No No

Most of the time, when someone says “a PSA test”, they mean total PSA. Free PSA is the extra measurement that sometimes gets added on top.

What ng/mL means

PSA results are given in nanograms per millilitre (ng/mL). It’s a concentration: how much PSA sits in each millilitre of blood. Some UK labs report in µg/L instead, which is numerically identical, so 4 ng/mL and 4 µg/L are the same thing. You’ll see both on NHS pathology pages.

How the free-to-total PSA ratio is calculated

The maths is friendly. Take your free PSA, divide it by your total PSA, then multiply by 100. The lab does both measurements on a single blood sample and works out the percentage for you, as one lab-testing guide describes.

A worked example:

  • Total PSA: 7.5 ng/mL
  • Free PSA: 1.5 ng/mL
  • 1.5 ÷ 7.5 = 0.2, and 0.2 × 100 = 20% free PSA

Same total, different free PSA, different story. If free PSA were only 0.6 ng/mL, you’d get 8%. If it were 2.25 ng/mL, you’d get 30%. The total hasn’t changed, but the proportion has, and the proportion is what the ratio is about.

The ratio is also called percent free PSA, free PSA ratio, or %fPSA. They all mean the same thing.

What a low or high percent free PSA can suggest

The general pattern is this:

  • A lower percentage of free PSA goes with a higher likelihood of prostate cancer.
  • A higher percentage of free PSA generally points to a lower risk, and often to benign prostatic hyperplasia (BPH), the non-cancerous enlargement that’s common as men get older. Harvard Health describes this pattern.

The reasoning is that cancer tends to produce PSA that’s more likely to be bound, so less is left floating free.

For a concrete number, North West London Pathology notes that in a healthy man with a total PSA of 4 to 10 µg/L, a free PSA of 10% or less raises the probability of a positive biopsy for prostate cancer about threefold. In that same range, the percentage can help tell prostate cancer from BPH.

Notice the conditions there: a healthy man, a total PSA between 4 and 10. The ratio is not a stand-alone verdict.

Why the 4 to 10 range matters

That middle band is the grey zone. A total PSA there could be cancer, BPH or inflammation, and the total alone can’t separate them. Some urologists measure free PSA at this point, and according to Harvard Health the result may sway the decision on whether to have a biopsy when combined with other tests.

If your total PSA is well below that range, the free PSA ratio usually isn’t needed. If it’s far above, other investigations take over.

There’s no single magic cut-off

You’ll see different thresholds quoted online, anything from around 10% up to 25%, depending on the lab, your age and your total PSA. That’s normal. Labs set their own reporting notes, and your clinician interprets the number for you. Please don’t self-score against a table you found on a forum.

The limits of the ratio

Let’s be real: this is a risk-adjusting tool, not a yes/no test. A few honest caveats:

  • It can’t diagnose or rule out cancer. Prostate Cancer UK is clear that a PSA blood test on its own can’t do either. It’s a first step to find men who may benefit from further tests such as an MRI scan, in its own words on PSA self-test kits.
  • Your GP looks at the whole picture. Age, risk factors, symptoms and general health all go into how your result is read.
  • Guidance differs by situation. There’s separate UK guidance for men with symptoms, where NICE focuses on referral, and for men without symptoms, where the PCRMP focuses on informed choice, as Prostate Cancer UK sets out for professionals.
  • Some results are borderline either way. A low ratio with a modest total can still turn out fine, and a decent ratio doesn’t give you a free pass if you have symptoms.

Things that can skew your PSA before you even test

A surprising amount can nudge a PSA number. Before any blood test, it helps to know the basics.

Before the test

The NHS advises avoiding ejaculation and vigorous exercise for 48 hours beforehand, because both can artificially raise levels (NHS PSA test page). Prostate Cancer UK adds that cycling may raise PSA for a few days. You can eat and drink as normal.

Medication

Drugs such as finasteride and dutasteride (5-alpha reductase inhibitors) can lower PSA by around 50%, and results are doubled for clinical interpretation, according to the NHS. If you take either, tell whoever reads your result.

Infection and catheters

A urine infection that’s still clearing, recent urinary retention or a catheter can all raise PSA. East Midlands Cancer Alliance guidance suggests considering a repeat test after about four weeks in those situations.

If any of this applies to you, mention it to your GP before reading much into a number.

Things that can skew your PSA before you even test — overview diagram

Getting a PSA test in the UK

A standard PSA test is a blood sample taken at a GP surgery and sent to a laboratory (Prostate Cancer UK). Over-50s and men who are at higher risk can ask for one after an informed chat about the pros and cons. Prostate Cancer UK also points out that current guidance may widen health inequalities, because men who are more health literate and better off are more likely to know to ask (PSA Consensus 2024). So if you’re unsure whether you qualify, ask. You’re allowed to.

If you have symptoms such as needing to pee more often, a weak flow or pain, book a GP appointment rather than waiting. If you’d like to talk it over first without sitting in a waiting room, an online men’s health consultation can be a useful way to get your questions in front of a doctor and plan next steps.

Where at-home PSA kits fit in

This is the part where we’ll be straight with you. Prostate Cancer UK advises against at-home PSA kits, citing concerns about how reliable the results are. Any home result should be treated as a prompt to talk to your GP, never as a diagnosis and never as reassurance to skip a check-up.

With that firmly in mind, some men like a quick, private way to find out whether it’s worth raising the subject. That’s the gap home screening aims to fill. Our men’s health screening range includes PSA and FOB (bowel) kits, with results in about 15 minutes, discreet packaging, free UK shipping and a 60-day refund guarantee if a kit doesn’t work. Our kits are CE-certified. A positive or worrying result means a GP conversation. A negative one doesn’t mean you can ignore symptoms.

Our view on all this

We built Rapidtest around a simple idea: plenty of people put off checking on their health because it’s a faff. Booking, waiting, the awkward bit of explaining. Men in particular tend to leave things until they can’t any more.

So we’re pro-checking, and pro-doing it properly. What does that mean for PSA?

Our view on all this — overview diagram

First, learn what the numbers are. Total PSA and free PSA aren’t scary once you know that one is the whole pot and the other is a slice of it. Second, don’t treat any single figure as a verdict, ours or a lab’s. The ratio exists precisely because one number isn’t enough. Third, use home screening as a nudge, not a replacement. If something looks off, go and see a doctor, and take your result with you.

That’s the line we’d want to hear from a friend: stay curious, stay calm, and follow up.

— Jack

A simple plan if you’ve got a result

  1. Write down both numbers. Total PSA and, if you have it, free PSA, with units (ng/mL or µg/L) and the date.
  2. Work out the percentage (free ÷ total × 100) if the lab hasn’t. It helps you follow what your GP says.
  3. Note anything that could have affected it: recent ejaculation or hard exercise, cycling, a urine infection, a catheter, or finasteride or dutasteride.
  4. Book a GP appointment to go through it, especially if the total is raised, the ratio is low, or you have symptoms.
  5. Ask what comes next. That might be a repeat test, an MRI scan or nothing yet. Let your GP decide with you.

FAQ

What is the difference between free and total PSA?

Total PSA is all the PSA in your blood, both bound to proteins and unattached. Free PSA is only the unattached part. Dividing free by total gives the percent free PSA, which some clinicians use to add detail to a borderline total result.

What is a good free PSA percentage?

In general, a higher percentage of free PSA suggests a lower risk of prostate cancer and is more often linked to BPH, while a low percentage, around 10% or below in the 4 to 10 range, is linked with a higher risk. There’s no universal pass mark, so ask your GP or the reporting lab how your number is read.

When is free PSA tested?

Usually when total PSA falls in the 4 to 10 ng/mL range and the picture is unclear. It’s not normally the first test. Your doctor may combine it with other information to decide whether further tests, such as a biopsy, make sense.

Can a high PSA mean something other than cancer?

Yes. BPH, infection, recent ejaculation, vigorous exercise or cycling and catheter use can all raise PSA. That’s why GPs read the result alongside your age, symptoms and history, and sometimes repeat the test.

Sources

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