Chapter 13: Diagnostic tests
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Evidence‐based approaches
Rationale
Detection of micro‐organisms in fluids that are normally sterile indicates significant infection (PHE [192]). Pleural fluid may be sent to the microbiology laboratory for bacterial culture to identify the cause of an effusion, isolate pathogenic micro‐organisms and establish susceptibility to antimicrobial therapy.
Indications
Obtaining a specimen of pleural fluid is indicated in patients with:
- bacterial pneumonia with radiological suggestion of significant pleural effusions
- systemic infection with pyrexia, severe pleuritic pain and leucocytosis
- suspected tuberculous focus with clinical signs or radiological evidence of significant pleural effusions (PHE [192]).
Methods of pleural fluid collection
Diagnosis of infection is established via the microbiological analysis of pleural fluid obtained by thoracocentesis using a strict aseptic technique, including meticulous skin antisepsis (Chernecky and Berger [32], Pagana and Pagana [177]).
Following clinical assessment and possibly radiological guidance, local anaesthetic is infiltrated into the area of intended thoracocentesis. A needle is advanced superiorly to the ribs to avoid neuromuscular bundle damage and to reduce the risk of causing a pneumothorax (Pendharkar and Tremblay [183]). Between 50 and 100 mL of fluid is drawn, transferred into a sterile container and sent to the laboratory for analysis.
The samples can initially be observed for characteristics such as colour and turbidity, and gram stains allow for direct observation of bacteria under a microscope. When bacterial infection of pleural fluid is suspected, a specimen should be drawn and inoculated directly into aerobic and anaerobic blood culture bottles (Pendharkar and Tremblay [183]).
Specimens should be dispatched to the laboratory immediately and liaison with the laboratory is essential to enable efficient processing of the sample. If there are any delays, the sample should be refrigerated at 4°C (PHE [192]).
