Gout or Septic Arthritis: How to Tell
The two conditions look almost identical, one is an emergency, and the blood tests people rely on do not separate them.
Part of the Complete Gout Guide.
Key fact: A hot, swollen joint should be treated as septic arthritis until proven otherwise. It cannot be told apart from gout on symptoms alone — both cause a red, hot, exquisitely painful joint — and a delay of days risks permanent joint destruction.
Why this distinction matters more than any other
Septic arthritis is infection inside the joint. Bacteria in a closed joint space destroy cartilage quickly, and the damage is not recoverable. It is treated as an orthopaedic emergency: joint aspiration, intravenous antibiotics, often surgical washout, and admission.
Gout, by contrast, is inflammation caused by urate crystals. It is painful and disabling, but it will not destroy the joint over a weekend.
The problem is that they present almost identically, and the person having their fifth gout flare is exactly the person most likely to assume this one is the same. British rheumatology guidance is deliberately blunt about it: any hot, swollen joint is considered septic until proven otherwise.
How similar they look
| Feature | Gout flare | Septic arthritis |
|---|---|---|
| Onset | Hours — often overnight | Hours to a couple of days |
| Single joint | Usually | Usually — about 80% of cases |
| Red, hot skin over the joint | Yes | Yes |
| Severe pain | Yes — often unable to bear weight | Yes |
| Raised temperature | Can happen with a bad flare | Common, but not always present |
| Raised inflammatory markers | Yes | Yes |
Every row that people rely on to tell them apart appears in both columns. That is the point of this page.
The features that shift suspicion
None of these is diagnostic, but each raises the concern enough to warrant same-day assessment:
- Feeling systemically unwell — fever with chills or rigors, nausea, confusion in an older person
- The joint cannot be moved at all, actively or passively. Septic arthritis classically restricts both; a gout flare is agonising but the joint can usually be moved a little
- A joint that is unusual for your gout — particularly a knee, hip or shoulder when your flares are normally in the foot
- It is getting worse after 48 hours of treatment that usually works
- A joint replacement or recent joint injection or surgery on that joint
- A break in the skin nearby — an ulcer, a wound, cellulitis or an injecting site
- You are immunosuppressed — by disease or by medication
Who is at higher risk of infection
- A prosthetic joint — infection rates are considerably higher than in a native joint, and treatment usually needs surgery
- Rheumatoid arthritis or existing joint damage, including osteoarthritis
- Diabetes
- Immunosuppression — steroids, biologics, chemotherapy, HIV
- Skin ulcers or chronic wounds
- Injecting drug use
- Heavy alcohol use — which is also a gout risk factor, so the two overlap
Several of these overlap with gout risk, which is precisely why they cannot be used to rule infection out.
Why blood tests do not settle it
Two blood tests get over-interpreted here.
- Inflammatory markers (CRP and ESR) rise in both. They are neither sensitive nor specific enough to distinguish them, and a normal result does not exclude infection. They should never delay assessment
- Serum urate is the bigger trap. A high urate level does not prove this episode is gout — plenty of people with a high urate have septic joints. And urate is often normal or low during an acute gout flare, so a normal result does not exclude gout either. What your uric acid level means covers this
"My uric acid is high, so it's gout" is not a safe conclusion. Having gout does not protect you from a joint infection. If anything, a joint already damaged by repeated flares is more vulnerable to one.
The test that does
Joint aspiration — drawing fluid out of the joint with a needle — is the test that answers the question. The fluid is sent for urgent Gram stain and culture, and examined under polarised light for crystals.
| Finding in joint fluid | Means |
|---|---|
| Needle-shaped, strongly negatively birefringent crystals | Urate crystals — gout |
| Rhomboid, weakly positively birefringent crystals | Calcium pyrophosphate — pseudogout |
| Organisms on Gram stain, or a positive culture | Septic arthritis |
Aspiration usually relieves pain as well as answering the question, and it is done in hospital rather than remotely. If someone proposes aspirating the joint, that is thoroughness rather than alarm.
What to do tonight
Contact NHS 111 or get an urgent appointment the same day if you have a hot, swollen, very painful joint and any of: a high temperature, chills or shivering, feeling sick or generally unwell, inability to move the joint at all, a joint replacement in that joint, a weakened immune system, or a wound or skin infection nearby. Call 999 if you are confused, very unwell, breathing fast, or your skin is mottled or cold — those suggest sepsis.
If you are waiting to be seen, do not take a steroid you have at home. Steroids dampen the signs of infection and can make assessment harder. An NSAID or paracetamol while you wait is reasonable if they are safe for you.
They can occur together
Gout and infection are not mutually exclusive. Finding urate crystals in the fluid does not exclude infection, which is why the fluid is cultured as well as examined for crystals, and why a clinician may start antibiotics while waiting for culture results even when crystals are seen.
The same logic applies to pseudogout, which is the other crystal arthritis and a common cause of an acutely hot knee in older adults. The differential for a painful, swollen joint covers how the crystal conditions and the non-crystal causes separate out.
Frequently Asked Questions
How do I know if my gout is infected?
You cannot tell reliably from symptoms, which is why any hot, swollen joint is treated as possible septic arthritis until proven otherwise. Features that raise concern are fever with chills, feeling generally unwell, being unable to move the joint at all, an unusual joint for your gout, a joint replacement, or no improvement after 48 hours of treatment that normally works.
Can a high uric acid level confirm it is gout and not infection?
No. A high urate level does not prove that this episode is gout, and urate is often normal or low during an acute flare, so a normal level does not exclude gout either. Only joint fluid analysis distinguishes crystal arthritis from infection.
What happens if septic arthritis is not treated quickly?
Bacteria in a closed joint space destroy cartilage rapidly and the damage is permanent. Untreated infection can also lead to osteomyelitis and sepsis. It is treated as an orthopaedic emergency with joint aspiration, intravenous antibiotics and often surgical washout.
Can you have gout and septic arthritis at the same time?
Yes. Finding urate crystals in joint fluid does not exclude infection, which is why the fluid is also cultured and why antibiotics may be started while results are awaited. A joint already damaged by repeated gout flares is more vulnerable to infection, not less.
Should I take my usual gout medicine while waiting to be seen?
Continue any long-term urate-lowering medicine such as allopurinol. Avoid taking an oral steroid you have at home, because steroids mask the signs of infection and make assessment harder. An NSAID or paracetamol while waiting is reasonable if those are safe for you.
References
- National Institute for Health and Care Excellence. Gout: diagnosis and management (NG219). nice.org.uk
- NHS. Gout. nhs.uk
- NHS. Septic arthritis. nhs.uk
- British Society for Rheumatology. Management of the hot swollen joint in adults. rheumatology.org.uk
- National Institute for Health and Care Excellence. Clinical Knowledge Summary: Gout. cks.nice.org.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. A hot, swollen joint should never be assumed to be gout without assessment, particularly alongside fever or feeling unwell. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.