Pericardial Fluid Analysis

Pericardial fluid analysis examines fluid removed from the pericardial sac (via pericardiocentesis). Tests include gross appearance, cell count and differential, protein, LDH, glucose, Gram stain/culture, cytology, acid‑fast bacilli/PCR and immunologic markers. Results help classify transudative vs exudative effusion and identify infection, malignancy, autoimmune disease or hemorrhage, guiding diagnosis and management of effusion and tamponade.

Normal pericardial fluid volume is about 15–50 mL of clear, straw-colored serous fluid within the pericardial sac. It lubricates heart movement and is mainly a plasma ultrafiltrate with small amounts of protein and cells. Volumes substantially above this constitute pericardial effusion and, depending on accumulation rate and pressure, can impair cardiac filling and cause tamponade.

Normal pericardial fluid is 15–50 mL, clear, with low cellularity and protein. Pathologic effusion is generally >50–100 mL or causes tamponade. Fluid analysis suggesting exudate: protein >3 g/dL, fluid/serum protein ratio ≈>0.5–0.6, or elevated LDH or fluid/serum LDH ratio >0.6. Hemorrhagic or chylous effusions are diagnosed by bloody appearance or triglycerides >110 mg/dL.

Pericardial fluid is obtained by pericardiocentesis: ultrasound (or CT)-guided needle aspiration through a subxiphoid, parasternal, or apical approach under sterile technique and local anaesthesia. Real-time echocardiographic and ECG monitoring minimize cardiac injury. Fluid may be sent for analysis; a pigtail catheter can be left for continuous drainage. Surgical pericardial window or pericardiectomy is used for loculated or recurrent effusions.

The four diagnostic criteria for acute pericarditis are: typical chest pain (sharp, pleuritic, improved by sitting up/leaning forward); a pericardial friction rub on auscultation; characteristic ECG changes (widespread ST‑segment elevation and/or PR depression); and new or worsening pericardial effusion on imaging. Diagnosis requires at least two of these findings. Further tests assess cause and complications.

Pericardial fluid's main function is to lubricate the space between visceral and parietal pericardial layers, minimizing friction as the heart moves and beats. It cushions and allows smooth, low-friction cardiac motion, helps prevent adhesions between layers, and contributes to maintaining optimal intrapericardial pressure for normal cardiac mechanics. Its small, regulated volume is essential; excess fluid or inflammation impairs heart function.