Body Fluid Panel



Body Fluid Panel

The serous body cavities are mesothelial lined potential spaces surrounding the lungs, heart and abdomen. Normally, they contain a small amount of fluid that is an ultrafiltrate of plasma. The maintenance of body fluids is a dynamic continuous process of formation and resorption. Formation of fluids is through the vascular system, which produces small amounts of ultra-filtrated plasma to lubricate body cavities and synovial joints, and to add bouancy to the central nervous system. Under normal conditions, the amount of fluid is small, but the body cavities represent potentially large spaces where fluid can accumulate. Excessive fluid (effusion) can accumulate if production is increased and/or resorption of fluid is decreased. When production and resorption of this ultrafiltrate are not balanced, fluid may accumulate, resulting in an effusion. Effusions may be classified as transudates or exudates.

Laboratory Evaluation

Excessive fluid can be removed from the body by procedures to provide relief from pressure symptoms, and to provide diagnostic studies.

The appearance of the pleural fluid and any odour should be noted.

|Fluid |Suspected disease |

|Putrid odour |Anaerobic empyema |

|Food particles |Oesophageal rupture |

|Bile stained |Cholothorax (biliary fistula) |

|Milky |Chylothorax/pseudochylothorax |

|Anchovy sauce” like fluid |Ruptured amoebic absces |

• The unpleasant aroma of anaerobic infection may guide antibiotic choice.

• The appearance can be divided into serous, blood tinged, frankly bloody, or purulent.

• Fluid is turbid or milky centrifuge it. Supernatant clear cell debris and empyema is likely.

• If it is still turbid, it is due to high lipid content and a chylothorax or pseudochylothorax are likely.

• If fluid appears bloody, a haematocrit can be obtained if there is doubt as to whether it is a haemothorax.

• If the haematocrit of the pleural fluid is more than half of the patient’s peripheral blood haematocrit, the patient has a haemothorax.

• If the haematocrit on the pleural fluid is less than 1%, the blood in the pleural fluid is not significant.

• Grossly bloody pleural fluid is usually due to malignancy, pulmonary embolus with infarction, trauma, benign asbestos pleural effusions, or post-cardiac injury syndrome (PCIS)

Fluids received in the laboratory often undergo four areas of testing

1) chemistry analysis

2) hematologic cell count and identification

3) microbiological stains and cultures and

4) cytopathologic examination.

The combination of these four areas of testing helps to identify the fluid as a transudate or an exudate, and in many cases provides information about the etiology of the fluid formation

Transudates are usually bilateral and arise from either increased capillary hydrostatic pressure or decreased oncotic pressure secondary to congestive heart failure, fluid overload, cirrhosis or hypoalbuminemia.

Causes of transudative pleural effusions

|Very common causes |Less common causes |Rare causes |

|Left ventricular failure |Nephrotic syndrome |Constrictive pericarditis |

|Liver cirrhosis |Mitral stenosis |Urinothorax |

|Hypoalbuminaemia |Pulmonary embolism |Superior vena cava obstruction |

|Peritoneal dialysis |Hypothyroidism |Ovarian hyperstimulation |

| | |Meigs’ syndrome |

Exudates are usually unilateral and result from increased capillary permeability or decreased lymphatic resorption associated with infection, connective tissue disease, pancreatitis or cancer.

/Exudates

Causes of exudative pleural effusions

|Common causes |Less common causes |Rare causes |

|Malignancy |Pulmonary infarction |Yellow nail syndrome |

|tuberculosis of lung |Rheumatoid arthritis |Drugs (see box 1) |

|Parapneumonic effusions |Autoimmune diseases |Fungal infections |

| |Benign asbestos effusion | |

| |Pancreatitis | |

| |Post-myocardial infarction syndrome | |

Several laboratory tests are helpful in distinguishing transudates from exudates including pH, total protein, lactate dehydrogenase (LD), amylase, glucose, white cell count and differential. Only one of these values has to fall into the exudate range for the effusion to be classified as an exudate. Large chemistry panels should not be ordered on body fluids.

Light’s criteria have been widely used to classify pleural and pericardial fluid as a transudate or an exudates.

Light’s Criteria

|Lab Test |Transudate |Exudate |

|Appearance |clear, pale yellow |turbid, bloody |

|Fluid total protein |3.0 g/dL or less |>3.0 g/dL |

|Fluid/serum protein |0.5 |

|Fluid/serum LD |0.6 |

|Fluid LD |0.67 x ULN serum |

|Cholesterol |7.3 suggests that resolution is possible with medical therapy alone. A pH < 7.2 suggests that a more complicated effusion or empyema requiring surgical drainage has probably formed. Pleural fluid pH should be measured with a blood gas analyzer and not with litmus paper or a pH meter, because both of the latter methods result in falsely elevated values.

A pleural fluid glucose < 60 mg/dL or a pleural fluid: serum glucose ratio < 0.5 may be seen in effusions caused by cancer, tuberculosis, empyema and rheumatoid arthritis.

Chylous Pleural Effusions

Chylous pleural effusions usually result from disruption or obstruction of the thoracic duct and are typically described as exudative lymphocytic pleural effusions with a milky appearance. Identifying chylothorax is important in determining the etiology of pleural effusion, but the biochemical parameters of chylous effusions have never been thoroughly analyzed. The criteria published in most medical textbooks were based on a small study published more than 30 years ago. Recently, investigators from the Mayo Clinic published their biochemical analysis of the pleural fluid obtained from 74 adults with a diagnosis of chylothorax (Mayo Clin Proc. Feb 2009;84(2)129-33). Gross appearance of the fluid was not a sensitive diagnostic criterion in identifying chylothorax. Only 44% of cases had the classic milky appearance attributed to chylothorax. A nonmilky appearance should not be used as a criterion to rule out a chylous effusion.

Most chylous effusions (86%) were classified as exudative effusions. Only 10% of the chylous effusions had lactate dehydrogenase levels in the exudative range. The traditional biochemical criterion for chylothorax is a pleural fluid triglyceride level greater than 110 mg/dL. The Mayo study validated this criterion. The mean+/-SD triglyceride value for transudative chylothoraces was 192+/-105 with a median of 195 mg/dL while the mean+/-SD triglyceride value for exudative chylothoraces was 855+/-816 with a median of 601 mg/dL. However, 14% of patients had triglyceride values less than 110 mg/dL, primarily due to perioperative fasting and malnourishment.

In cases of suspected chylous effusion with triglycerides less than 110 mg/dL, the specimen can be sent to a reference laboratory for lipoprotein electrophoresis. The presence of chlyomicrons in the fluid supports the diagnosis of chylothorax.

Causes of chylothorax and pseudochylothorax

Chylothorax

|Chylothorax |Pseudochylothorax |

|Neoplasm: lympho ma, metastatic carcinoma |Tuberculosis |

|Trauma: operative, penetrating injuries |Rheumatoid arthritis |

|Miscellaneous: tuberculosis, sarcoidosis, |Poorly treated empyema |

|lymphangioleiomyomatosis, cirrhosis, obstruction of central | |

|veins, amyloidosis | |

| | |

Differential cell counts on the pleural fluid

• Pleural lymphocytosis is common in malignancy and tuberculosis.

• Eosinophilic pleural effusions are not always benign.

When polymorphonuclear cells predominate, the patient has an acute process affecting the pleural surfaces. If there is concomitant parenchymal shadowing, the most likely diagnoses are parapneumonic effusion and pulmonary embolism with infarction.

If there is no parenchymal shadowing, more frequent diagnoses are pulmonary embolism, viral infection, acute tuberculosis, or benign asbestos pleural effusion.

Eosinophilic pleural effusion is defined as the presence of 10% or more eosinophils in the pleural fluid. The presence of pleural fluid eosinophilia is of little use in the differential diagnosis of pleural effusions. Benign aetiologies include parapneumonic effusions, tuberculosis, drug induced pleurisy,benign asbestos pleural effusions, Churg-Strauss syndrome, pulmonary infarction, and parasitic disease.18–20 It is often the result of air or blood in the pleural cavity.19 However, malignancy is also a common cause; 11 of a series of 45 eosinophilic effusions were due to cancer.20

If the pleural fluid differential cell count shows a predominant lymphocytosis, the most likely diagnoses are tuberculosis and malignancy. Although high lymphocyte counts in pleural fluid raise the possibility of tuberculous pleurisy,9 as many as 10% of tuberculous pleural effusions are predominantly neutrophilic.21 Lymphoma, sarcoidosis, rheumatoid disease, and chylothorax can cause a lymphocytic pleural effusion.22

Coronary artery bypass grafting (CABG) often causes pleural effusions which can usually be treated conservatively.

Large symptomatic effusions can occur in up to 1% of patients in the postoperative period. These are predominantly left sided and the differential cell count can help to clarify the situation.

Bloody effusions are usually eosinophilic, occur early, and are related to bleeding into the pleural cavity from the time of surgery.

Non-bloody effusions tend to have small lymphocytes as their predominant cell type, occur later, and are generally more difficult to treat.

• pH should be performed in all non-purulent effusions.[B]

• In an infected effusion a pH of ................
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