Laboratory Studies
The following laboratory studies are not required for diagnosis but are useful to determine the metabolic and nutritional status of the patient:
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Serum electrolyte tests
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Serum albumin test
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Complete blood cell (CBC) count with differential to assess for lymphocyte depletion
Imaging Studies
Chest radiographic findings are nonspecific for chylothorax and indistinguishable from other causes of pleural effusion; however, they may help to rule out other causes of the patient's symptoms. [4] Determine if effusion is bilateral. Look for a mediastinal shift.
The 2017 American College of Radiology (ACR) Appropriateness Criteria indicates that if the etiology of the chylothorax is unknown, obtain computed tomography (CT) scanning or magnetic resonance imaging (MRI) of the chest and abdomen for evaluation of the lymphatic vessels, and to rule out vascular abnormalities and/or malignancy. [4] The addition of contrast medium to CT scanning of the chest and abdomen may be useful when venous thrombosis is a suspected cause for chylothorax. [4]
Lymphangiography is useful when the anatomy of the thoracic duct needs to be defined preoperatively or when the site of the leak is not clinically obvious, and it may facilitate minimally invasive management when it is being considered. [4] Lymphoscintigraphy is also useful for the localization of the leak, evaluation of the thoracic duct patency, and differentiation of partial from complete thoracic duct transection. [14]
Procedures
Thoracentesis and pleural fluid analysis are the criterion standards to establish a diagnosis of chylothorax. Alternatively, in a postsurgical patient, tube thoracostomy output can be analyzed.
Pleural fluid analysis for triglyceride content helps to confirm the diagnosis of chylothorax. Note the following:
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A level greater than 110 mg/dL reflects a 99% chance that the fluid is chyle.
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A level less than 50 mg/dL reflects only a 5% chance that the fluid is chyle.
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If the level is 50-110 mg/dL, use lipoprotein analysis or inspect the pleural fluid for chylomicrons or cholesterol crystals.
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A ratio of pleural fluid cholesterol to triglyceride of less than 1 is also diagnostic.
A fasting patient may have serous-appearing pleural fluid. To confirm the diagnosis, administer cream through a nasoenteric tube prior to fluid collection. The cream will change the chylous production from serous to the characteristic milky white fluid. This change is diagnostic for a chyle leak.
Chylothorax can be distinguished from pseudochylothorax by fluid analysis. In pseudochylothorax, the cholesterol level is greater than 200 mg/dL, no chylomicrons are present, and cholesterol crystals are seen at microscopy.
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This anteroposterior upright chest radiograph shows a massive left-sided pleural effusion with contralateral mediastinal shift. Image courtesy of Allen R Thomas, MD.
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This computed tomography scan of the chest of a 3-year old child reveals a left-sided effusion and underlying parenchymal infiltrate and atelectasis. Image courtesy of Ibrahim Abdulhamid, MD.
