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Pericardial Fluid Analysis: How Valuable Is It?
Abstract & Commentary
By Michael H. Crawford, MD, Professor of Medicine, and Chief of Clinical Cardiology, at the University of California, San Francisco. Dr. Crawford is on the speaker's bureau for Pfizer.
Source: Ben-Horin S, et al. Diagnostic Value of the Biochemical Composition of Pericardial Effusions in Patients Undergoing Pericardiocentesis. Am J Cardiol. 2007;99:1294-1297.
The biochemical analysis of pericardial fluid is often done routinely, but there is little data on its value. Thus, these investigators from Israel retrospectively analyzed all pericardiocentesis patients over a 9-year period by chart review and phone calls. The causes of pericardial fluid were determined using standard diagnostic criteria, and idiopathic was defined when no cause was found over a 6-mnth or more follow-up. The study population consisted of 120 patients out of 173 who had biochemical studies and were followed for an average of 18 months. Patients with malignant effusions accounted for most of the mortality observed (41 of 59 deaths). Neoplastic effusions were more often bloody, but there was too much overlap with other causes to use this feature diagnostically. This was true for all bio-chemical tests as well. There were some findings that suggested a diagnosis. Bacterial effusions often had a low fluid-to-serum glucose ratio (0.3) and a low lymphocyte fraction (8%). The highest neutrophil counts were seen in patients with acute pericarditis (7.8), collagen vascular disease (7.5) and post pericardectomy (5.0). Only 2 of the 120 effusions could be classified as transudates based upon pleural fluid criteria using lactic dehydrogenase and protein levels. Also, no combination of tests accurately diagnosed any condition or group of like conditions. The authors concluded that almost all pericardial effusions are exudates and the measurement of biochemical and cell count parameters is not useful for determining the cause of the effusion.
I am frequently asked by primary care doctors or other specialist to tap an asymptomatic pericardial effusion in order to make a diagnosis of the cause of the fluid accumulation. I have resisted these requests under the assumption that the risks of the procedure outweigh the diagnostic value. This article supports the general lack of value of pericardial fluid for etiologic diagnosis. However, the study is not definitive because of a number of problems. It is retrospective, so no specific protocol was used for pericardial effusion evaluation. In fact, 53 had no analysis done of their fluid and were excluded from the study. In these patients either the doctors involved had already made up their minds about the value of pericardial fluid analysis or they believed the diagnosis was obvious. A specific protocol, prospectively applied, may have performed better. The study population was small and dominated by 3 diagnoses (neoplastic 42, idiopathic 22, acute 17). The other 9 diagnoses had 10 patients or less in each diagnostic category. The results in the latter cases could be different if more patients were studied in each category. Some diagnoses could probably be inferred from other data such as uremic, traumatic and radiation. Finally, we are not given the reason for pericardiocentesis or the complication rate. Clearly the pleural fluid paradigm of transudate vs exudate does not apply to pericardial fluid. Was any measure of value? Perhaps percent lymphocytes which were markedly lower in bacterial pericarditis or collagen vascular disease, but there was too much overlap with other diagnoses to be definitive. In conclusion, pericardiocentesis should only be done for tamponade or impending tamponade and the fluid should only be sent or cell counts, culture and possibly glucose.