My knee is hot, red and swollen. Is it gout or an infection?

The short verdict

Treat a suddenly hot, swollen knee as a possible infection until a doctor has ruled it out. Gout is far more common and is painful but not usually dangerous to the joint in the short term. Septic arthritis is less common, but bacteria inside the joint can destroy cartilage quickly and can spread into the blood. Because the two overlap so much, the safe approach is to be assessed the same day.

How they compare

• Onset: gout often starts overnight or over a few hours; infection usually builds over one to two days
• Fever and feeling unwell: possible with both, but shivers, fever and feeling generally ill point more towards infection
• History: previous gout attacks, a big meal or dehydration favour gout; a recent injection, a cut on the knee, surgery, diabetes or a weak immune system raise concern for infection
• Movement: both can make the knee hard to bend, but an infected knee is often too painful to move at all
• Blood tests: inflammation markers are often raised in both, so they rarely settle the question alone
• The deciding test: drawing fluid from the knee and looking for crystals and bacteria

Importantly, a person can have gout and an infection at the same time, so finding crystals does not always end the investigation.

Who each diagnosis tends to suit

Gout tends to affect men from middle age and women after menopause, people with high uric acid, kidney problems or on some water tablets, and outdoor workers in Qatar who become dehydrated in the heat. Septic arthritis is more likely in older adults, people with diabetes, those with an existing knee replacement, after a recent knee injection or operation, and in anyone with a skin infection near the joint.

When to seek care in Doha

Go to emergency the same day if your knee is hot, swollen and too painful to bear weight, especially with fever, shivers, or a recent injection or surgery. If you have a knee replacement and it suddenly becomes hot and swollen, do not wait. For recurring flares once infection has been excluded, Dr. Gelber at Aman Hospital can review your knee, the fluid results and long-term prevention with your physician.