Cell Count, Serous Fluid

CPT: 89051
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Test Details


Evaluate serous fluid for the presence of RBCs (semiquantitative), WBCs, differential, and for physical appearance


Total leukocyte counts are of limited value in the differential diagnosis of pleural and pericardial effusions.1,2 For completely clotted serous fluid specimens, actual cell counts will not be performed. Morphology will still be assessed by cytocentrifuged, stained slides. Routine cytological evaluations would be indicated to confirm or rule out suspected neoplastic or tumor cells, malignancy.1 The total leukocyte count may be useful in distinguishing between peritoneal transudates (eg, in uncomplicated cirrhosis) from spontaneous bacterial peritonitis (SBP) caused by passage of bacteria from blood to ascitic fluid.1


Microscopic and macroscopic examination

Additional Information

To minimize unnecessary laboratory testing it is important to have a clear differential diagnosis in mind. Results of these studies should always be correlated with clinical findings and any other ancillary studies to determine an accurate diagnosis.1

Gross examination can play a vital role in determining the pathogenesis of the effusion. Transudates are usually clear and pale yellow and do not clot.1

Pleural or pericardial fluids: Exudates are cloudy to purulent and often clot while standing because of the presence of fibrinogen. Exudative fluid usually contains large numbers of leukocytes and elevated protein content. Occasionally, exudates may be straw-colored, similar to transudates. A cloudy, purulent fluid is usually associated with an infectious process.1

Peritoneal fluid: Exudates are cloudy or turbid due to large numbers of leukocytes, elevated protein concentrations, and/or microörganisms. Such fluids may be seen in peritonitis, perforated or infracted intestine, and pancreatitis.1

Cell types seen on examination of a cytoprep-stained slide include mesothelial cells, which form the lining of pleural, pericardial, and peritoneal cavities. Sometimes, it is impossible to differentiate mesothelial cells from malignant cells. Mesothelial cells are seen in variable numbers in most effusions and are increased in sterile inflammations caused by such conditions as pneumonia, pulmonary infarction, and malignant disorders. Mononuclear phagocytes (monocytes, histocytes, and macrophages) are usually seen in variable numbers in pleural, pericardial, and peritoneal effusions. Since both monocytes and mesothelial cells may be transformed into macrophages, the distinction between them is not always obvious. Lymphocytes are seen in variable numbers in most serous effusions. Plasma cells may be seen in fluid specimens of patients with rheumatoid arthritis, malignant disorders, tuberculosis, and other conditions associated with lymphocytosis. Neutrophils may vary in number, but a predominance suggests a bacterial pneumonia, pulmonary infarction, or pancreatitis and bacterial peritonitis. Eosinophils can be seen in a wide variety of disorders, including pneumothorax, idiopathic effusions, infections, neoplasms, chronic peritoneal dialysis, congestive heart failure, vasculitis, and malignant lymphomas. Basophils are unusual in serous fluid, but usually accompany eosinophils.1

Specimen Requirements


Serous fluid


1 to 2 mL

Minimum Volume

0.5 mL (Note: This volume does not allow for repeat testing.)


Lavender-top (EDTA) tube or green-top (heparin) tube


Follow standard collection procedures. Heparin should be added to the syringe used for aspiration of pleural or pericardial fluid to prevent clotting.1

Storage Instructions

Refrigerate at 2°C to 8°C; stable 48 hours.

Stability Requirements



Room temperature



2 days (48 hours)



Freeze/thaw cycles


Causes for Rejection

Room temperature storage; frozen specimen; improperly labeled specimen; quantity not sufficient for analysis; gel-barrier tube

Clinical Information


1. Kjeldsberg K, Knight J. Body Fluids. 3rd ed. Chicago, Ill: ASCP Press;1993:161-170.
2. Dines DE, Pierre RV, Franzen SJ. The value of cells in the pleural fluid in the differential diagnosis. Mayo Clin Proc. 1975 Oct; 50(10):571-572. 1165648


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
005240 Cell Ct, Serous Fluid 005241 Color, Serous 6824-7
005240 Cell Ct, Serous Fluid 005242 Clarity, Serous 9335-1
005240 Cell Ct, Serous Fluid 005244 Nucleated Cells, Serous /mm3 55793-4
005240 Cell Ct, Serous Fluid 005245 RBC, Serous /uL 23860-0
005240 Cell Ct, Serous Fluid 005246 Polys, Serous % 12238-2
005240 Cell Ct, Serous Fluid 005250 Lymphocytes, Serous % 13941-0
005240 Cell Ct, Serous Fluid 005251 Macrophages, Serous % 12230-9
005240 Cell Ct, Serous Fluid 005252 Eosinophils, Serous % 12209-3
005240 Cell Ct, Serous Fluid 005253 Lining Cells, Serous % 35477-9
005240 Cell Ct, Serous Fluid 005254 Comments: 20999-9

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