Diagnosis of mastitis is mainly clinical however, some patients with mastitis may have a positive bacterial culture of breast milk^[1] although culture is rarely used to confirm bacterial infection of the milk because positive cultures can result from normal bacterial colonization, and negative cultures do not rule out mastitis.^[2] Complete blood count may show an elevated neutrophil count although this is not specific to mastitis.

Common laboratory investigations used include:

• Culture of breast milk

• Some patients with mastitis have a positive bacterial culture of breast milk.^[1] Culture is rarely used to confirm bacterial infection of the milk because positive cultures can result from normal bacterial colonization, and negative cultures do not rule out mastitis. Culture has been recommended when the infection is severe, unusual, or hospital acquired, or if it fails to respond to two days’ treatment with appropriate antibiotics.^[2]

• Complete blood count may show an elevated neutrophil count although this is not specific to mastitis.