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In many cases, staph infections may be initially suspected based on the patient’s symptoms. A physician will perform a complete physical examination and compile a thorough medical history to make a diagnosis.

A probable diagnosis may be confirmed by taking staph bacteria from a sample of material from the site of the infection. The bacteria may be confirmed by their appearance when viewed under a microscope. In addition, bacteria may be cultured by isolating and growing the bacteria and observing its response to a variety of chemicals. This can help identify what type of medication, if any, may be necessary to treat it. However, because staph bacteria may be present on the body without causing illness, multiple cultures may be required to rule out other potential causes of a patient’s symptoms. Staph cultures may take several days to complete.

Sites from which samples may be taken include:

In addition to culturing the bacteria, other tests may be necessary to confirm a diagnosis of a staph infection. These methods include:

• Blood tests. A complete blood count (CBC) is a routine blood test that measures the composition of cells within the blood. This may reveal an elevated level of white blood cells, which indicates the presence of infection. Other types of blood tests may also be performed.
  
  
• Imaging tests. To view possible abnormal changes to internal tissues, x-rays, an MRI (magnetic resonance imaging), echocardiogram or CAT scan (computed axial tomography) may be used. These imaging tests are often able to show any damage to the bones, muscles or joints caused by a staph infection.