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Diagnosis of Pleural Effusion


Diagnosis of Pleural Effusion

Thoracentesis may be performed for diagnosis or therapy. The classical pattern of examination includes inspection of the respiratory system, palpation, percussion (tapping) and auscultation.

Diagnosis of pleural effusion begins with elicitation of a proper medical history of the patient. Examination includes inspection of the respiratory system, palpation, percussion (tapping) and auscultation. Air entry is usually restricted by fluid collection, percussion classically yields a ‘stony dull’ note. A friction rub or squeak may be heard if there is inflammation of the pleura (pleurisy).

  • Radiologic Examination is of great aid in the diagnosis of pleural effusion. X-rays taken in the ‘posteroanterior view’ have to be supplemented with a lateral decubitus view (obtained with the patient lying on the side of the effusion).  Chest ultrasound and CT scan also help the process of diagnosis.
  • Thoracentesis and Pleural Fluid Analysis

Thoracentesis may be performed for diagnosis or therapy. A long thin needle is injected into the pleural space to remove fluid that is sent for testing to confirm the diagnosis. This is also used for treatment. As a rule, newly discovered effusions should be tapped. A number of conditions act as relative contraindications for tapping. These include bleeding diathesis, anticoagulation, a small volume of fluid, mechanical ventilation, and a low benefit-to-risk ratio.

While diagnostic tapping takes 30 to 50 ml of pleural fluid for analysis, therapeutic tapping takes a larger amount (no more than 1000 to 1500 mL at one time).

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  • Chemical analysis helps to differentiate a transudate from an exudate. Exudates have higher protein concentrations than transudates. LDH (lactate dehydrogenase) level also act as a distinguishing factor between the two. Analysis of cell count, culture can reveal infections and malignancies.

Light's criteria for exudates–any of following:

Pleural fluid/serum protein ratio > 0.5

Pleural fluid/serum LDH ratio > 0.6

Pleural fluid LDH >23 the normal upper limit for serum 

  • Biopsy may be indicated in selective cases.
  • Further examination may be required to diagnose the underlying cause.

Alternate diagnoses (Differential diagnoses) include hemothorax (blood collection in the cavity), pneumothorax (presence of air) and empyema (collection of pus).

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