INTRODUCTION

Body fluids are lubricating fluids present within the body cavities. Normally, a small amount of fluid is present within the body cavities which keeps the surfaces moist and lubricated so that the movement of the adjacent or the opposing membrane surfaces occurs with minimal friction. Increase in the volume of the fluid in these cavities is known as effusion. 

The commonly examined body fluids in the laboratory include:

  1. pleural, 
  2. pericardial, 
  3. peritoneal and 
  4. synovial fluid.

Effusions may be broadly divided into transudate and exudate; the differences between them are shown in Table 51.1.

Specimen Collection

The body fluid is collected in a clean, dry container under aseptic precautions and atraumatically to avoid mixing with fresh blood. 

The fluid is collected in the following three sterile test tubes:

•• Chemical examination: Fluoride tube

•• Microscopic examination: EDTA tube

•• Bacteriological examination: Plain tube (without anticoagulant).

They should be examined as early as possible to prevent chemical changes, growth of bacteria and disintegration of cells.

EXAMINATION OF BODY FLUIDS

Physical Examination

Note volume, color and appearance.

Color: Pleural, pericardial and ascitic (peritoneal)fluids are usually clear and straw colored.

•• Uniform blood stained fluid suggests malignancy involving the organs/tissues surrounding the respective body cavity (Table 51.2).

•• Turbid fluid may be due to high cell count or high protein content.

•• Chylous with milky appearance usually indicates high lipid content due to lymphatic obstruction.

Transudate vs. exudate:

It is important to differentiate whether the fluid is a transudate or exudate (Table 51.1).

•• Transudate is usually seen in all body cavities with diseases like heart failure and hypoalbuminemic conditions (e.g. nephrotic syndrome). Cirrhosis results in prominent ascites, but may also cause pleural effusion.

•• Exudate usually suggests infection or malignancy.

Chemical Examination

•• Protein estimation:

This helps to differentiate transudate from exudate (Table 51.1).

•• Glucose estimation:

Low glucose in the body fluids usually suggests bacterial infection(including tuberculosis), malignancy or nonspecific inflammation.

•• Measurement of amylase in ascitic fluid in patients with pancreatic lesions.

Microscopic Examination

•• Cell count is done similar to total WBC count using improved Neubauer chamber.

–– Normal: Few mesothelial cells (lining cells of body cavities) and lymphocytes are seen.

•• Differential WBC count

Procedure: Centrifuge the body fluid and from the sediment prepare the smears (at least 2).

Stains:

–– Leishman’s stain: Stain one smear with Leishman’s stain and count 100 cells and express the differential count.

–– Gram’s stain/acid fast stain: These stains are useful in suspected cases of infective/tubercular infections.

•• Cytological examination for malignant cells

–– Procedure: The body fluid is centrifuged; smears are made from the sediment and fixed immediately in absolute alcohol. The smears are stained by Papanicolaou stain. Hematoxylin and eosin stain or Giemsa may also be used.

–– Cytospin is a better alternative for making smears.

Microbiological Examination

Culture is done to identify the organism in cases of effusion due to infections.

Normal composition of pleural fluid is mentioned in Table 51.3.

EXAMINATION OF SYNOVIAL FLUIDS

Uses

Examination of synovial fluid is useful in the diagnosis of joint disorders.

•• Infective arthritis (septic arthritis, rheumatic).

•• Gouty arthritis (metabolic disorder).

•• Rheumatoid arthritis (autoimmune disorder).

•• Degenerative arthritis.

Laboratory Examination

It consists of:

(1) physical examination, 

(2) microscopic examination, 

(3) chemical examination, and 

(4) microbiological examination.


Physical Examination

a. Color and appearance (Table 51.4)

b. Viscosity test

Synovial fluid is viscous due to the presence of hyaluronic acid. The viscosity of the synovial fluid decreases in inflammatory joint disorders due to the breakdown of hyaluronic acid by the enzyme hyaluronidase.

c. Mucin clot test

Hyaluronic acid forms a compact clot when mixed with the acetic acid. Low concentration of hyaluronic acid does not allow the formation of a firm clot. Add few drops of synovial fluid to 20 mL of 5% acetic acid in a small beaker. A good clot is formed if the synovial fluid is normal.

•• In inflammatory diseases of the joint, there is poor clot formation due to degrading enzymes from the inflammatory cells (e.g. tuberculous arthritis).

•• Noninflammatory joint disorders show good clot formation whereas hemorrhagic synovial fluid prevents clot formation due to dilution of fluid.

•• Fair to poorly formed clot is seen in rheumatoid arthritis, gout and pseudo gout.

Microscopic Examination

•• The total leukocyte count:

is estimated similar to total WBC count using improved Neubauerchamber.

•• Differential leukocyte count:

–– If polymorphs are more than 70%, it indicates bacterial arthritis.

–– Noninflammatory arthropathies (osteoarthritis) are associated with lymphocytes and macrophages.

•• Wet smear examination:

Centrifuge the synovial fluid and take the sediment on a glass slide and cover it with a coverslip. Observe the slide first under low power objective, then under high power objective with reduced light and carefully note for the presence of following crystals:

–– Urate crystals are needle shaped, highly birefringent and are seen in gouty arthritis.

–– Rhomboid calcium pyrophosphate crystals are seen in pseudo-gout.

–– Cholesterol crystals are seen in rheumatoid arthritis.

–– Crystals can be confirmed using polarized microscopy.

Chemical Examination

•• Glucose estimation: Significance is similar to glucose in the body fluids.

•• Protein estimation: Significance is similar to proteins in the body fluids.

Microbiological Examination

Synovial fluid culture is recommended in suspected cases of pyogenic/tubercular arthritis.

Points to note

•• Body fluids are normally present in small amounts within body cavities. Increase in the volume of the fluid in these cavities is known as effusion.

•• Commonly examined body fluids include pleural, pericardial, peritoneal and synovial fluid. It is important to differentiate whether the fluid is a transudate or an exudate.

•• Examination of body fluid consists of physical, microscopic, chemical and microbiological examination. 

In physical examination volume, color and appearance are noted. Microscopically, fluids are examined for total number of cells, types of cells and malignant cells, if any. Chemical examination consists of estimation of glucose, protein and other specific tests depending on the type of body fluid.

 Culture of the fluid is done in cases with inflammatory or infective disorders.

•• In synovial fluid, wet smear examination can be done to identify the crystals.