Difference Between Pleural Effusion and Pneumonia l Pleural Effusion vs Pneumonia

Key Difference – Pleural Effusion vs Pneumonia

Pleural effusion and pneumonia are two conditions that affect our respiratory system. Pleural effusion is actually a complication of many illnesses that directly or indirectly exert an adverse impact on the airways and lung parenchyma whereas pneumonia is one such illness that can give rise to pleural effusion. This is the key difference between these two. Medically pleural effusion can be defined as an excessive accumulation of fluid in the pleural space is known as a pleural effusion. On the other hand, pneumonia can be defined as the invasion of lung parenchyma by microorganisms.


1. Overview and Key Difference
2. What is Pleural Effusion
3. What is Pneumonia
4. Similarities Between Pleural Effusion and Pneumonia
5. Side by Side Comparison – Pleural Effusion vs Pneumonia in Tabular Form
6. Summary

What is Pleural Effusion?

An excessive accumulation of fluid in the pleural space is known as a pleural effusion. This condition can be identified by a chest x-ray if the fluid level is more than 300ml. But clinical identification of pleural effusion is possible only when the amount of fluid is more than 500ml.

Transudate Pleural Effusion

Pleural effusions of transudate type can be bilateral but more fluid accumulates in the right side than on the left side.

Characteristics of Transudate Pleural Effusion

  • Protein content is less than 30 g/l
  • Lactic dehydrogenase level is less than 200 IU/L
  • Fluid to serum LDH ratio is smaller than 0.6


  • Heart failure
  • Hypoproteinaemia
  • Constrictive pericarditis
  • Hypothyroidism
  • Ovarian tumors producing right-sided pleural effusion

Exudate Pleural Effusion

Exudate pleural effusions have the following hallmark features

  • Protein content is more than 30 g/l
  • Lactic dehydrogenase level is more than 200 IU/L


  • Bacterial pneumonia
  • Pulmonary infarction
  • Bronchial carcinoma
  • TB
  • Autoimmune rheumatic disease
  • Post-myocardial infarction syndrome
  • Acute pancreatitis
  • Mesothelioma
  • Sarcoidosis

Clinical Features

  • Dyspnea
  • Dry cough
  • Orthopnea
  • Chest pain
  • In case of an infection, there can be other nonspecific symptoms such as fever
  • Hemoptysis


A chest X-ray is taken immediately when a patient presents with the tale-telling symptoms of pleural effusion. Once the X-ray confirms the clinical suspicion of a pleural effusion, an ultrasound-guided pleural aspiration is carried out.