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Lab Test: Bilirubin, Conjugated, Direct (Blood) Level

    Lab Test
    • Bilirubin(Conjugated; Blood)
    Description
    • Measurement of direct (conjugated) bilirubin in serum to evaluate liver function and bilirubin metabolism.  It is part of the evaluation of adult patients with hemolytic anemias and newborns with jaundice.
    Reference Range
    • Adults:  0.1-0.3 mg/dL (1.7-5.1 micromol/L)
    • Neonates:  < 1 mg/dL with normal total bilirubin
    Indications & Uses
    • Suspected abnormal liver function in sickle cell (Hb S disease) - effect on direct bilirubin due (due to chronic hemolysis) with common liver function abnormalities associated with sickle cell disease include:
      • Markedly increased:  obstructive cholelithiasis, transfusion hepatitis, or acute hepatic cirrhosis
      • Slightly increased:  transfusion hemosiderosis
    • Suspected hepatitis - the total bilirubin level is divided between conjugated (direct) and unconjugated (indirect) studies.  A marked increase in the bilirubin level ranging from 5 to 20 mg/dL may occur 3.5 to 5.5 months after exposure; an elevation of greater than 20 mg/dL suggests severe disease.  Conjugated and unconjugated levels usually parallel each other, except in the rare complication of aplastic anemia when unconjugated bilirubin prevails.
    • Suspected neonatal hyperbilirubinemia - conjugated hyperbilirubinemia is defined as a direct (conjugated) serum bilirubin level greater than 1 mg/dL if the total bilirubin is less than 5 mg/dL or as a direct bilirubin level more than 20% of total bilirubin if the total bilirubin level is greater than 5 mg/dL.  If conjugated serum bilirubin is elevated, cholestasis is present and prompt stepwise clinical evaluation is necessary.
    • Suspected obstructive jaundice - elevated direct bilurbin levels may occur in choledocholithiasis or gallstone pancreatitis but are not reliable for diagnosing choledocholithiasis.  History and physical exam may be the only indicator of common bile duct stones.
    • If one value of the liver profile is elevated (alkaline phosphatase, AST, lactate dehydrogenase, or bilirubin), common bile duct stones will found in 20% of cases.  With two elevated values, the risk doubles, and with three elevated values, more than half of the patients will have choledocholithiasis.
    Clinical Application

    Bile is formed in the liver and may constituents, including bilirubin.  Bilirubin metabolism begins with the breakdown of red blood cells (RBCs) in the reticuloendothelial system (mostly the spleen).  Hemoglobin is released from RBCs and broken down to heme and globin molecules.  Heme is then catabolized to form biliverdin, which is transformed to bilirubin.  This is unconjugated (indirect) bilirubin which is conjugated with a glucuronie molecule in the liver, resulting in conjugated (direct) bilirubin. 

    Jaundice is the discoloration of body tissues caused by abnormally high blood levels of bilirubin.  Jaundice results from a defect in the normal metabolism or excretion of bilirubin.  This defect can occur at any stage of heme catabolism.


    Increased levels:
    • Gallstones
    • Extrahepatic duct obstruction (tumor, inflammation, gallstone, scarring, surgical trauma) - these diseases cause a blockage of the bile ducts.  Since bile cannot be excreted, blood levels rise.
    • Extensive liver metastasis - the intrahepatic ducts or hepatic ducts become obstructed because of tumor.  Bile cannot be excreted and blood levels rise.
    • Cholestasis from drugs - some drugs inhibit the excretion of bile from the hepatocyte into the bile canaliculi.  Bile cannot be excreted and blood levels rise.
    • Dubin-Johnson syndrome and rotor syndrome - congenital defects in enzyme quantity inhibit metabolism and excretion of bilirubin and blood levels rise.
    Related Tests
    • Liver enzymes such as alkaline phosphatase (ALP), lactic dehydrogenase (LDH), aspartate aminotransferase (AST) alanine aminotransferase (ALT), and 5'-nucleotidase
    • Complete blood cell count, haptoglobinm and other blood tests.  These tests are helpful in the evaluation of hemolytic anemias. 
    • Comprehensive metabolic panel
    • Hemolysis panel
    • Hepatic function panel
    • Transfusion reaction workup Transplant panel
    Drug-Lab Interactions
    • Blood hemolysis and lipemia can produce erroneous results.
    Test Tube Needed
    • Red-top
    Procedure
    • Fasting requirements may vary among different laboratories.  Some require keeping the patient on nothing by mouth (NPO) status after midnight the day of the test except for water
    • Collect a venous blood sample.
    • Use a heel puncture for blood collection in infants.
    • Prevent hemolysis of blood during phlebotomy.
    • Apply pressure or a pressure dressing to the venipuncture site and assess the site for bleeding.
    • Patients with jaundice nay have prolonged clotting times.
    Storage and Handling
    • Protect specimen from light to avoid formation of photobilirubin.
    • Do not shake the tube, because inaccurate test results may occur.
    • Serum or heparinized plasma may be used for Ektachem 700 method
    What To Tell Patient Before & After
    • Explain the procedure to the patient.
    References
    • LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests.  First ed. Montvale, NJ: Thomson PDR; 2007.
    • Pagana K, Pagana TJ eds. Mosby's Manual of Diagnostic and Laboratory Tests. 5th Ed.  St. Louis, Missouri. 2014.

MESH Terms & Keywords

  • Bilirubin, Conjugated, Direct