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What does yellow color of pleural fluid mean?

Pleural fluid is the liquid that surrounds the lungs. Normally, only a thin layer of pleural fluid is present between the two pleural membranes that line the chest cavity and cover the lungs. This helps lubricate the lungs and allows them to move smoothly during breathing.

The color of normal pleural fluid is clear to pale yellow. However, pleural fluid can become yellow and cloudy or turbid when there is an abnormal buildup of fluid in the pleural space. This condition is known as a pleural effusion.

Causes of Yellow Pleural Fluid

There are several possible causes of yellow pleural fluid:

  • Infection – Bacterial infections like pneumonia can cause yellow pus to accumulate in the pleural space. This is known as empyema.
  • Cancer – Lung cancer, breast cancer, lymphoma and other cancers can cause malignant pleural effusions with bloody or straw-colored fluid.
  • Pulmonary embolism – Blood clots in the lungs can lead to fluid leakage into the pleural space.
  • Heart failure – Fluid can back up into the lungs due to congestive heart failure.
  • Liver cirrhosis – Abnormal function of the liver allows fluid to build up in the chest.
  • Autoimmune disorders – Conditions like rheumatoid arthritis and lupus can cause inflammation and fluid buildup.
  • Pancreatitis – Inflammation of the pancreas allows pancreatic enzymes to irritate the pleura.
  • Trauma – Injuries like rib fractures or lung contusions can lead to hematomas and bloody pleural effusions.

Diagnostic Tests

If a pleural effusion is suspected, doctors can perform diagnostic tests to determine the cause of the fluid buildup. These may include:

  • Chest x-ray – Can visualize pleural effusions.
  • Thoracentesis – Insertion of a needle to drain and analyze pleural fluid.
  • CT scan – Provides detailed images of the lungs and pleural space.
  • Pleural fluid analysis – Fluid is sent to the lab to check cell counts, protein, glucose, pH, cultures, cytology.
  • Pleural biopsy – Taking a small sample of the pleura for examination under a microscope.

Appearance of Yellow Pleural Fluid

The appearance of pleural fluid can provide clues as to the underlying cause:

  • Clear, yellow fluid – This can be seen with heart failure, cirrhosis, and pulmonary embolism. The fluid is transudative in nature.
  • Cloudy, yellow-green fluid – This suggests bacterial infection and empyema. The cloudiness is due to pus and dead white blood cells.
  • Dark yellow, bloody fluid – This raises suspicion for malignancy or trauma causing bloody pleural effusions.
  • Milky, yellow fluid – A high triglyceride level from chronic pancreatitis or esophageal rupture can result in fluid that appears milky.

Pleural Fluid Analysis

Once a sample of pleural fluid is obtained through thoracentesis, it undergoes laboratory analysis. This allows doctors to determine what is causing the effusion. Tests performed may include:

  • Cell counts – The number of red blood cells, white blood cells and cell types help indicate infectious, malignant or other causes.
  • Glucose, protein and LDH – Levels help distinguish exudative from transudative effusions.
  • pH – Low pH suggests complicated parapneumonic effusions or rheumatoid pleurisy.
  • Gram stain and culture – Identify bacterial pathogens in empyema.
  • Cytology – Microscopic examination of cells to check for cancer.


Treatment of a pleural effusion depends on the underlying cause. Possible treatments include:

  • Antibiotics for infectious effusions like empyema.
  • Thoracentesis to drain large effusions and relieve shortness of breath.
  • Tube thoracostomy placement for continual drainage of fluid buildup.
  • Treating the underlying condition, like heart failure or liver disease.
  • Chemotherapy or radiation if the effusion is due to lung cancer.
  • Pleurodesis to adhere the pleural membranes together and prevent fluid return.


The prognosis for yellow pleural effusions depends on the cause. Empyemas have a good prognosis if treated early with antibiotics and drainage. Malignant effusions related to advanced lung cancer may have a poorer prognosis.

With appropriate treatment, many patients experience relief of symptoms and improvement in lung function once the excess fluid is removed. However, the effusion may return if the underlying condition cannot be successfully treated.

Key Points

  • Yellow pleural fluid is abnormal and signifies an effusion or buildup of excess fluid.
  • Common causes include infection, cancer, heart failure, liver disease, pulmonary embolism, and trauma.
  • Diagnostic tests like thoracentesis, chest x-ray, CT scan, and pleural fluid analysis help determine the cause.
  • Treatment depends on the underlying condition but may include drainage, antibiotics, chemotherapy, or pleurodesis.
  • Prognosis varies depending on the cause but is generally good if treated appropriately.


In summary, yellow pleural fluid is an abnormal finding indicating some form of pleural effusion. Determining the cause through diagnostic testing is important, as treatment options can vary. With appropriate management, many patients see improvement in symptoms and lung function. The prognosis ultimately depends on the underlying condition leading to the buildup of yellow fluid in the pleural space.

Cause Appearance Tests Treatment Prognosis
Infection (empyema) Cloudy, greenish-yellow Cell count, culture Antibiotics, drainage Good with treatment
Cancer Dark yellow, bloody Cytology, biopsy Chemotherapy, radiation, pleurodesis Varies depending on cancer
Heart failure Clear, yellow Fluid protein, LDH Drainage, treat heart failure Good with treatment
Liver disease Clear, yellow Fluid protein, LDH Drainage, treat liver disease Good with treatment
Pulmonary embolism Clear, yellow CT scan, d-dimer Anticoagulation, drainage Good with treatment

This table summarizes the common causes, appearance, diagnostic tests, treatments and prognosis for yellow pleural effusions. Infectious causes like empyema tend to have the best outcomes when treated. Malignant effusions can have variable prognoses depending on the type and stage of cancer. Heart failure, liver disease and PE related effusions also carry relatively good prognoses with appropriate treatment. The key is determining the cause through analysis of the pleural fluid and other tests, so that proper treatment can be initiated.