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ID:790 Pleural fluid pH
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DescriptionSerous fluids may be classified as transudates or exudates. Transudates are derived from ultrafiltration across a membrane and have a low protein content, whereas exudates are formed by active secretion and have a high protein content. Pleural fluid forms a film about 10 um thick between the visceral and parietal pleural surfaces and is usually <1 ml in volume. Pneumonia leads to about 50,000 hospital admissions each year in the UK. Approximately 57% of such patients will develop pleural fluid. This is referred to as a ôsimple parapneumonic effusion. When the pleural fluid has developed features of infection but is not yet overtly purulent, the early fibrinopurulent stage, this is referred to as complicated parapneumonic effusion. Pleural fluid containing frank pus (infection + white cells) is referred to as empyema. A simple parapnuemonic effusion can be treated by antibiotics alone whereas both a complicated parapneumonic effusion and frank pus require chest tube drainage. The British Thoracic Society (Thorax 2003;58(Suppl II):ii8-ii17) recommends fluid pH as a means of differentiating between a simple parapneumonic effusion (pH>7.2) and a complicated parapneumonic effusion (pH <7.2). Previously, Blood Gas Analyser pH was recommended as the only way to determine pH in pleural fluid where the result was to be used for decision making (Chest 1998;114:1368-1372).
IndicationDifferentiating between a simple parapneumonic effusion (pH>7.2) and a complicated parapneumonic effusion (pH <7.2).
Additional Info
Concurrent Testsna
Dietary Requirementsna

InterpretationpH >7.2 indicates a simple parapneumonic effusion; pH <7.2 indicates a complicated parapneumonic effusion

Ref. Range (Male)
Ref. Range (Female)
Ref. Range (Paed)
Ref. Range Notes
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IP Acute TAT- Not Defined -
IP Routine TAT- Not Defined -
GP Acute TAT- Not Defined -
GP Routine TAT- Not Defined -
Turnround CommentNA
Originally edited by : Mike Bosomworth. Last edited on 25/05/2018 08:20:38. Published By A Garner on 25/05/2017 08:20:38.