Pleural Fluid for Amylase

Function

The Pleural Fluid Amylase test measures the concentration of the enzyme amylase within the fluid collected from the pleural space (the area between the lungs and the chest wall). Under normal physiological conditions, very little fluid exists in this space, and its amylase concentration should not exceed that of the blood. Amylase is primarily produced by the pancreas and salivary glands to digest carbohydrates.

Why it is Ordered

This test is ordered when a patient develops a pleural effusion (excess fluid around the lungs) and the physician suspects a specific underlying cause related to the pancreas or the esophagus. It is a critical diagnostic tool for differentiating the etiology of an 'exudative' effusion. Specifically, it helps identify:

• Acute or Chronic Pancreatitis: Where enzymes leak into the pleural space.
• Esophageal Rupture: A medical emergency where salivary amylase enters the chest cavity.
• Malignancy: Certain lung or ovarian cancers can produce amylase.

Associated Conditions

• Pancreatic Pseudocyst: Fluid collections from the pancreas can track into the thorax.
• Boerhaave Syndrome: Spontaneous esophageal perforation usually following forceful vomiting.
• Paraneoplastic Syndrome: Ectopic production of amylase by tumor cells.

Interpretation

High levels (often defined as greater than the upper limit of serum amylase or >100 U/L) are highly suggestive of pancreatic disease or esophageal perforation. In pancreatic cases, the amylase is usually the pancreatic isoenzyme, whereas in esophageal rupture or malignancy, it is often the salivary isoenzyme. Clinicians use this result alongside Light’s Criteria to manage the effusion effectively.