Your doctor can usually diagnose mastitis based on your symptoms and an examination of the affected breast. Tests are usually not needed. But they may be done to confirm a diagnosis or to help guide treatment for other problems that can develop.

Breast milk culture

If you have an infection that isn't improving with treatment, your doctor may do a breast milk culture. To provide a sample for a culture, you will squeeze a small sample of milk from the affected breast onto a sterile swab. The culture results help your doctor confirm a diagnosis and to find out the specific bacteria that are causing the infection.

Occasionally, it takes more than one round of antibiotics to clear a breast infection. If you have not been responding to antibiotic treatment, culture results may be used to determine the most effective antibiotic for you.

Abscess

Sometimes a pocket of pus (abscess) forms in the reddened area of the breast. If an abscess is too deep to examine by touching it, your health professional may use a breast ultrasound to examine it. Ultrasound can also be used to guide a needle to an abscess that needs to be drained of fluid. A culture of the abscess fluid is usually done to identify the infecting organism.