The human body has several sites that contain fluid or have the ability to accumulate large quantities of fluid when afflicted by disease. The chest cavities surrounding the lungs and the abdominal cavity are good examples of these. Body fluid samples are commonly collected for testing to help reach a diagnosis. One of these tests involves counting the numbers and types of cells present in the fluid.
Body Fluid
The body cavities surrounding the lungs and abdominal organs are lined by smooth tissue membranes. These cavities normally contain only small amounts of lubricating fluid that allow easy movement of the organs. The fluid is a filtrate of blood plasma, consisting of watery, clear fluid with only small amounts of protein and low numbers of cells, according to "Clinical Diagnosis and Management by Laboratory Methods." Different diseases can cause increased fluid accumulation, with associated changes in proteins and cell count. This abnormal fluid collection is called an effusion.
Sampling an Effusion
Effusions are often sampled and diagnostic tests performed to aid in reaching a diagnosis. A sterile needle is inserted into the body cavity using local anesthetic by a physician or other trained health care practitioner, as outlined in the Merck Manual. A portion of the fluid is drawn into a container and transported to the laboratory for evaluation. The tests ordered include a protein level, cell count and microbiology exam with culture. The number and types of cells in the fluid are counted either by automated instrument or under a microscope. Cytology studies may also be performed if cancer is suspected.
Body Fluid Cell Count
Each body cavity has somewhat different cell numbers under normal conditions, according to the Mayo Medical Laboratories. Red cell numbers should be very low in all these sites. White, or inflammatory, cell numbers should be less than 500/uL. Effusions consisting of clear watery fluid with low protein levels and relatively low cell counts are called transudates. Transudates are associated with circulatory problems such as congestive heart failure, liver cirrhosis or low blood protein levels. Effusions consisting of cloudy, thick fluid, elevated protein levels and high cell counts are called exudates. Exudates are associated with infection, other inflammatory conditions or cancer.
Cell Types in Body Fluids
Total cell numbers in fluids are informative, but the types of cells in the count are also important, as discussed in "Clinical Diagnosis and Management by Laboratory Methods." Predominantly large numbers of red cells indicate trauma or other injury, with bleeding into the cavity. The types of inflammatory cell present can help differentiate between infections due to bacteria, virus or parasites or other inflammatory conditions without infection. Malignant cells can be identified, confirming a diagnosis of cancer.
Interpretation
Body cavity effusions always indicate an abnormal condition. The cell count and types of cells present are important clues in determining the cause of an effusion, especially when used in combination with an individual's medical history, physical examination and other tests performed.
References
- "Clinical Diagnosis and Management by Laboratory Methods," Nineteenth Edition; John B. Henry M.D., Editor; 1996
- Merck Manual: GI Procedures for the Generalist
- Mayo Medical Laboratories: Cell Count and Differential, Body Fluids
