Emergency Evaluation of Effusions — Sample Handling, Cell Identification, Important Findings

Emergency Evaluation of Effusions — Sample Handling, Cell Identification, Important Findings

Aug 01, 2007

An acute abdomen is defined as the acute onset of abdominal pain. Possible underlying etiologies are broad ranging, and include the gamut from trauma to infectious and neoplastic causes. An effusion is defined as the escape of fluid into a part. Effusive processes can occur in essentially every tissue in the body. The ability to obtain this fluid for cytologic evaluation limits the types of samples that are amenable to examination. Synovial fluid, aqueous humor, cerebrospinal fluid and serous body cavity fluids are all routinely evaluated in veterinary medicine. Obtaining and rapidly assessing effusions are keys to the diagnosis, choice and institution of therapy, and the ultimate outcome of many cases.

Normal effusions are due to a combination of factors including Starlings forces, pressure differential across the visceral pleura that favors absorption, lymphatic drainage, mesothelial cell activity and the stoma between mesothelial cells. The different cavities can have a large, ongoing exchange of fluid and solute, yet a low, stable volume is maintained. Crudely, effusions form when there is an imbalance between formation and resorption

The power of the clincopathologic evaluation of effusions is undeniable. Using widely available tools and instruments, samples can be obtained with minimal risk to the patients, yet the diagnostic yield can be tremendous, depending on the specific disease entity present. The indication to obtain and evaluate fluid is often determined based on the history, physical examination, radiographic / ultrasonographic findings or other finding.

The proper handling of fluid can dramatically affect the diagnostic yield from samples otherwise properly obtained. If in doubt, contact your reference lab for details concerning submissions. EDTA containing tubes are ideal for cytologic analysis, as it provides the best morphology, with minimal distortion if smears are made relatively quickly. This tube can also be used for determination of the total nucleated cell count (TNCC) / white blood cell (WBC) count, total protein (TP) (assessed by refractometry) and packed cell volume (PCV). If cells are left in EDTA tubes, they will age naturally and artifactually become vacuolated. Likewise, if left in tube, in vitro phagocytosis (RBCs, bacteria, WBCs, etc.) will occur. EDTA is bacteriostatic and therefore not appropriate for culture. Tubes without additive (i.e. red topped tubes) can be utilized if any biochemical assays are to be performed on the sample. Although not ideal, they can be used for culture, mainly aerobic. Even clear samples can contain enough fibrin to compromise cytologic evaluation. Serum separator tubes (SST) should be avoided, as the gel can entrap cells and severely compromise cytologic evaluation. These tubes are likely ok for biochemical analysis. Culture tubes / Culturettes are often utilized based on cytologic findings. These should be utilized if cultures are to be performed. Individual labs may have specific media for specific tests (e.g. Mycobacterium sp., fungal isolation, virus isolation, anaerobic bacteria, etc.) and/or for transportation, especially if there will be a delay between sample acquisition and processing. If no better options are available, a sample can be submitted in the syringe for culture as long as it was obtained using sterile technique. The air should be expressed out of the syringe and securely capped. If possible, centrifuged sediment should also be submitted on media for culture. Heparin containing tubes can be used for biochemical assays, especially STAT samples

Unless otherwise noted, sample preparation should be done using fluid from the EDTA. Direct smears using the blood smear technique is an extremely simple, fast technique to visualize nucleated cells in an effusion that has moderately high to high TNCC (>10,000/μl). This is the preparation that should be consulted if there are concerns about true, in vivo changes to cells and/or structures in the background. A drop of the fluid is placed on one end of a clean, new slide. The spreader slide is backed up into the drop, which then spreads towards, but not to the sides. The spreader slide is then advanced off the slide in one firm, smooth motion, producing a bullet shaped smear: