From the Guidelines
Bilirubin labs are crucial for assessing liver function and identifying the cause of jaundice, with both total and fractionated levels necessary for proper evaluation, as indicated by the most recent study 1. When evaluating bilirubin, it is essential to consider the different types of bilirubin, including direct (conjugated) and indirect (unconjugated) bilirubin.
- Normal total bilirubin ranges from 0.3-1.0 mg/dL, with elevated levels above 2-3 mg/dL typically causing visible jaundice.
- Increased direct bilirubin suggests problems with bile excretion, such as biliary obstruction or certain liver diseases, while elevated indirect bilirubin points to conditions like hemolysis or Gilbert's syndrome, as discussed in 1. Key considerations for accurate bilirubin testing include:
- Fasting for 4 hours before testing to minimize dietary influences on bilirubin levels.
- Protecting the sample from light, as bilirubin degrades with light exposure, which can lead to inaccurate results.
- Serial measurements are often more valuable than single readings, especially when monitoring conditions like neonatal jaundice or tracking response to treatment, as emphasized in 1. Bilirubin elevation patterns help distinguish between pre-hepatic (hemolysis), hepatic (liver disease), and post-hepatic (biliary obstruction) causes of jaundice, making these tests crucial diagnostic tools in hepatology and general medicine, with the most recent study 1 providing the strongest evidence for this approach.
From the Research
Bilirubin Labs
- Bilirubin labs are used to evaluate jaundice in adults, which is an indication of hyperbilirubinemia and can be caused by derangements in bilirubin metabolism 2, 3.
- The initial laboratory evaluation for jaundice should include assays for bilirubin (total and fractionated), as well as other tests such as a complete blood cell count, liver function tests, and coagulation studies 2, 3.
- Measuring fractionated bilirubin allows for determination of whether the hyperbilirubinemia is conjugated or unconjugated, which can help differentiate between potential causes such as hemolysis, liver disease, or biliary obstruction 2, 3, 4.
- Elevated plasma bilirubin levels can be secondary to alterations in any stage of its metabolism, including excess bilirubin production, impaired liver uptake, impaired conjugation, or bile clearance defect 5.
- Various analytical methods are available for measuring bilirubin and its metabolites in serum, urine, and feces, including diazo transfer reaction, high-performance liquid chromatography (HPLC), and direct spectrophotometry 5.
Causes of Hyperbilirubinemia
- Unconjugated hyperbilirubinemia can occur with increased bilirubin production caused by red blood cell destruction, such as hemolytic disorders, and disorders of impaired bilirubin conjugation, such as Gilbert syndrome 3, 4.
- Conjugated hyperbilirubinemia can occur in disorders of hepatocellular damage, such as viral and alcoholic hepatitis, and cholestatic disorders, such as choledocholithiasis and neoplastic obstruction of the biliary tree 3, 4.
- Posthepatic disorders, such as gallstone formation, biliary tract infection, pancreatitis, and malignancies, can also cause conjugated hyperbilirubinemia 4.
Diagnostic Evaluation
- The evaluation of jaundice relies on a careful history and physical examination, followed by directed imaging of the biliary tree and liver 2, 3, 6.
- Ultrasonography of the abdomen, computed tomography with intravenous contrast media, and magnetic resonance cholangiopancreatography are first-line options for patients presenting with jaundice, depending on the suspected underlying etiology 2.
- Liver biopsy may be required to establish the diagnosis, prognosis, and management of the disease if the etiology of jaundice is unclear despite laboratory testing and imaging 2.