About Liver Function Tests for Dengue Fever
Dengue fever is a mosquito-borne infectious disease endemic to wet, tropical regions. The most severe cases result in hemorrhagic fever, vascular permeability, liver impairment and possible death. Differential diagnosis of putative dengue fever includes examination for rash, fever, signs of hemorrhage and vascular permeability, and clinical analysis of blood samples for complete blood count (CBC), albumin and liver function tests. This article explores the use of liver function tests in dengue fever diagnoses.
Significance
Dengue fever is endemic in Southeast Asia, Africa, the Pacific and tropical regions of the Americas. There are between 50 and 100 million annual cases of dengue fever infection worldwide, with several hundred thousand manifesting as dengue hemorrhagic fever (DHF). The hemorrhagic form is fatal in 5 percent of patients. Travelers to dengue endemic regions result in between 100 and 200 cases of dengue fever occurring in the United States each year.
Identification
Liver function testing is one tool in the diagnosis of dengue fever. Patients presenting with fever, flu-like symptoms, headache, ocular pain and rash in areas of dengue endemicity should receive a complete blood work-up, including a liver function test.
Doctors should also consider dengue fever in patients with a recent travel history to dengue endemic regions.
Physical exam may reveal an enlarged liver (2 to 4 cm below costal margin); liver enlargement more frequently occurs in severe cases of dengue shock syndrome.
Function
Liver function tests (LFTs) measure levels of bilirubin, ammonia and enzymes present in patient blood samples. Elevated results are non-specific to dengue fever; serology and viral isolation provide definitive confirmation of dengue infection.
Bilirubin is a breakdown product of blood hemoglobin and causes the distinct pigment of liver bile. Increased levels of unconjugated bilirubin indicate hepatic dysfunction related to liver disease or infection rather than obstruction. Increased bilirubin levels may present clinically as jaundice. Jaundice is rarely present in dengue fever patients.
Ammonia is normally converted to urea by the liver before excretion in urine. Elevated levels indicate impaired liver function.
Elevation of liver enzymes such as aspartame aminotransferase (AST), alkaline phosphotase (AST), alkaline phosphotase (ALP) and gamma-glutymyl transferase (GGT) also indicate hepatic impairment.
Elevated liver function test results may indicate a number of chronic and acute diseases and infections including liver cirrhosis, mononucleosis, hepatitis and heart disease. For this reason, interpretation of results must take the complete clinical picture into consideration when using a liver function test to diagnosis dengue fever.
Features
Patients with dengue fever will exhibit elevated results on liver function tests. Liver function tests detect elevated levels of aspartame aminotransferase (AST), alanine aminotransferase (ALT) and gamma-glutamyl transpeptidase (GGT) enzymes in the majority of dengue fever patients. A smaller proportion of dengue fever patients will also exhibit elevated levels of bilirubin and alkaline phosphatase.
Elevation of ALT and AST is generally mild to moderate in most dengue fever patients, but may be more than one magnitude higher than normal upper limits. Higher limits are often associated with hemorrhagic manifestations.
AST levels are generally higher than AST levels. Liver enzyme levels generally peak by day 9 in dengue fever patients and return within normal limits within 2 weeks of dengue fever onset.
Warning
Liver function test results for dengue fever do not differ significantly from those obtained for hepatitis B and hepatitis C patients; co-infection is also a distinct possibility. When considering viral hepatitis diagnosis in a patient from a region with endemic dengue fever, consider dengue fever as a causative agent of elevated liver function test results.
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