In the healthy adult, pericardial fluid ranges from 10 to 50 mL, produced similarly as in the pleura.

Pericardial effusions are mainly due to phlogistic and/or neoplastic processes that compromise the integrity of the permeability of endothelial and mesothelial cells, and induce obstruction of the lymphatic pathways of the affected area.

Pericardial fluid is pale yellow and clear. Large effusions (>350 mL) are due to neoplastic infiltration (lymphoproliferative neoplasms or metastatic processes), uremia or microbial agents (bacterial, tubercular, or fungal infections), inflammatory processes, autoimmune diseases, cardiac infarction with mediastinal damage, and iatrogenic causes. The most frequent cause of idiopathic pericardial effusion is enterovirus infections. Patients with HIV infection often present with asymptomatic pericardial effusions that increase as the infectious disease progresses.

Pericardial fluid may be hematic due to incorrect sampling maneuver (with penetration of the heart chambers) or in the case of a hemorrhagic effusion, with correct sampling. In the latter case, the hematocrit or the number of red blood cells is lower than that of the blood. Moreover, in the first case the sample coagulates, in the second case this is very rare.

Post-pericardiotomy syndrome may occur in subjects undergoing cardiac surgery, who are still in hospital but sometimes already at home. It is characterized by fever, thoracic- pleural pain, and other signs of pleural, pericardial, and, less frequently, pulmonary inflammation. In more than 80% of cases, a pleural exudate develops, which is serous to frankly hematic, with pH > 7.4 and normal glucose levels. There are no specific laboratory tests except for detection of anti-myocardial antibodies and, serum C3, which may be decreased.

Table 1 shows the main laboratory tests performed in pericardial fluid.

Table1. Brief description of the main laboratory tests on the pericardial fluid and related interpretative criteria

Macroscopic Evaluation and Cellular Analysis

 Pericardial fluid for diagnostic purposes is obtained by peri cardiotomy or pericardiocentesis.

Normal pericardial fluid or fluid of exudative origin is generally clear yellow, whereas the fluid is turbid in exudative effusions, such as neoplastic or infected effusions. Finally, as described above, pericardial fluid may sometimes have a hemorrhagic appearance.

The mean value of cellularity can range from a minimum of 10 × 10⁶/L to a maximum of 1900–2210 × 10⁶/L cells. In contrast, the mean value ranges from 3600 × 10⁶/L up to 14,116 × 10⁶/L cells in pericardial effusions of probable neoplastic origin.

The effusions of bacterial or rheumatic etiology are generally characterized by the presence of about 70% of neutrophil granulocytes, while those secondary to hypothyroidism and/or neoplastic nature are characterized by 75% or more of monocytes or other mononuclear cells. Distinguishing activated mesothelial cells from neoplastic cells often requires further investigation, in addition to purely morphological ones.

Biochemistry

Light’s criteria for distinguishing an exudate from a transudate also apply to pericardial fluid. However, the literature data do not show adequate specificity and sensitivity and, even if applied, have not been validated for this type of fluid; further studies, possibly multicentric and with large numbers, are necessary (Table 1). Glucose, total protein, pH, lipids, lactate dehydrogenase (LDH), and adenosine deaminase (ADA) should be assayed on this fluid.

A glucose concentration <40 mg/dL is frequent in bacterial, tubercular, rheumatic, or neoplastic effusions. Higher glucose values have less diagnostic value.

A protein concentration < 3.0 g/dL has a sensitivity of 97% for an exudate, but a much lower specificity (around 22%), resulting in poor utility.

The pH of pericardial fluid can be markedly decreased ( <7.1 ) in rheumatic and purulent pericarditis. Pathologies such as neoplasms, uremia, tuberculosis, and idiopathic forms show a moderate decrease in pH (7.2–7.3).

Triglyceride and cholesterol assays may be useful in distinguishing between chylous and pseudochylous effusions, along with lipoprotein electrophoresis, which is useful in checking for the presence of chylomicrons. In pericardial fluid, LDH >200 U/L (i.e., pericardial fluid LDH/ plasma LDH ratio >0.6) is characteristic of an exudate.

The ADA increases significantly in tubercular pericarditis, at a cutoff of 30 U/L the sensitivity exceeds 90%, while the specificity does not reach 70%. By raising the cutoff to 40 U/L, both sensitivity and specificity exceed 90%.

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