Test for Infection

​Where inflammation is active needle aspiration of synovial fluid is necessary to conduct PCR testing for infection, with or without culture tests. Culture-based tests are not sufficiently sensitive to detect all types of infection.

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In cases of prior injury or surgical procedure it is important to test the synovial fluid in the affected joint for infection. Synovial fluid is extracted by needle aspiration of the joint, often after flushing with sterile saline solution. Infections tests are particularly important for people with a prosthesis or metal “hardware” that microorganisms can adhere to.

Chronic low-grade infections often do not have the classic symptoms of redness, heat and swelling that are typical of acute infections, and may be missed by surgeons. This, together with the need for highly sensitive infection tests, means that chronic low-grade infections are notoriously difficult to diagnose. The traditional culture test is not adequately sensitive.

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In addition to a culture test a molecular test called a PCR and sequencing should be performed on the synovial fluid. This test is more sensitive for identifying low numbers of bacteria that may be present in the joint. Next generation sequencing is a more advanced and powerful molecular test that is capable of identifying multiple microorganisms if these are present. 

Identification of microorganisms using molecular techniques permits the appropriate antibiotic (or other medication) to be prescribed.

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It is also necessary to rule out infection prior to taking anti-inflammatory medications, since these increase the risk of infection.