Before making a diagnosis of shoulder bursitis, tendinitis, or shoulder impingement, a doctor must rule out other common problems that could cause shoulder pain, including shoulder osteoarthritis.
To identify the root cause of shoulder pain, a doctor will use some or all of the diagnostic tools described below.
- Gram stain. A Gram stain is a lab test performed to detect the presence of problematic bacteria. However, a Gram stain cannot reveal all bacteria, so even if the test comes back negative, septic bursitis cannot be completely ruled out.
- White blood cell count. An elevated number of white blood cells in the bursa’s synovial fluid indicates an infection.
- Glucose levels test. Below-normal glucose levels may indicative of an infection.
Patient interview. A doctor will record the patient’s medical history, details about the onset of his or her symptoms, the pattern of pain and swelling, and how everyday activities have been affected. A patient’s reported symptoms are important to diagnosis and treatment.
Physical exam. A doctor will examine the patient’s joint, noting swelling, tenderness, and pain points. The doctor also will perform a series of physical tests, such as raising the patient’s arm overhead and across the body to evaluate mobility and pain.
X-rays, ultrasound, MRI. A doctor may order an x-ray to determine if the root cause of the shoulder pain is osteoarthritis or a bone abnormality. An ultrasound or MRI can provide a detailed view of the soft tissue and may be used to detect abnormalities such as a thickened or swollen bursa or damaged tendon or muscle.
Anesthetic Injection. One way to tell if the pain is related to shoulder impingement syndrome is to inject an anesthetic called lidocaine hydrochloride under the shoulder’s acromion. If the injection relieves the pain, impingement syndrome is the likely cause.
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Aspiration and lab tests. Septic shoulder bursitis, in which the bursa is infected by microorganisms (e.g. bacteria), is not common but it does occur. If septic shoulder bursitis is suspected, a doctor may perform an aspiration, removing fluid from the bursa with a needle and syringe.
In addition to relieving pressure and making the patient more comfortable, it provides a fluid sample that can be analyzed for infection using the tests below.
Occasionally, lab tests to detect infection are negative even when an infection is present. Therefore, a doctor who suspects septic bursitis may prescribe antibiotics without definitive positive lab tests.