Doctors often diagnose cellulitis by looking at your symptoms. In most cases, you won't need further testing, and your doctor will prescribe antibiotics.

Sometimes ultrasound will be used to make sure there is not a blood clot in a deep vein. A CT scan or an MRI may also be done to rule out other problems.

If the initial treatment with antibiotics is not effective, your health professional may take samples of your blood and skin to identify the specific bacteria present so he or she can select a more effective antibiotic. Other lab tests usually are not helpful unless bacteremia (bacteria in the blood), sepsis, or another underlying disease is suspected.