Bilirubin (total and direct)
The two bilirubin fractions
The distinction between direct and indirect bilirubin is fundamental in identifying the mechanism responsible for hyperbilirubinemia. Each fraction points to a different type of pathology.
| Fraction | Other name | Features | Normal values (adult) |
|---|---|---|---|
| Total bilirubin | BT | Sum of direct and indirect fractions | 3 - 21 µmol/L |
| Direct bilirubin | Conjugated bilirubin | Transformed by the liver, water-soluble, excreted in bile | 0 - 8 µmol/L (≤ 30 % of total) |
| Indirect bilirubin | Unconjugated bilirubin | Bound to albumin, not water-soluble, not excreted by the kidneys | Calculated: BT - BD (≤ 17 µmol/L) |
Bilirubin metabolism: from the red blood cell to elimination
Understanding the body's bilirubin circuit enables us to better interpret abnormalities according to the stage affected:
- Destruction of aged red blood cells in the spleen: release of hemoglobin, conversion to unconjugated bilirubin (indirect)
- Blood transport: indirect bilirubin circulates bound to albumin, insoluble in water
- Hepatic uptake: hepatocytes capture indirect bilirubin and conjugate it with glucuronic acid (direct bilirubin)
- Biliary excretion: direct bilirubin is secreted into the bile, stored in the gallbladder, then discharged into the intestine.
- Intestinal transformation: intestinal bacteria convert bilirubin into urobilinogen, which is partly reabsorbed and eliminated in the urine (urobilin, responsible for its yellow color), and stercobilin (responsible for the brown color of stools).
Causes of elevation by dominant fraction
Analysis of the fractions can rapidly orient the diagnosis towards three main categories of jaundice: pre-hepatic, hepatic or post-hepatic.
| Type of jaundice | High fraction | Mechanism | Common causes |
|---|---|---|---|
| Pre-hepatic (hemolytic) | Indirect bilirubin | Excessive bilirubin production exceeding the liver's conjugation capacity | Hemolytic anemia, sickle cell anemia, spherocytosis, malaria, incompatible transfusions |
| Hepatic (hepatocellular) | The two fractions (mixed) | Hepatocyte damage reduces conjugation and excretion | Viral hepatitis (A, B, C), alcoholic hepatitis, cirrhosis, steatohepatitis, hepatotoxic drugs |
| Post-hepatic (cholestatic) | Direct bilirubin | Obstruction of bile ducts preventing excretion of conjugated bilirubin | Biliary lithiasis, pancreatic cancer, biliary cancer, sclerosing cholangitis, tumor compression |
| Gilbert's syndrome | Indirect bilirubin (light) | Benign conjugation enzyme deficiency (UGT1A1), accentuated by fasting or fatigue | Benign genetic condition, without significant liver damage |
| Neonatal jaundice | Indirect bilirubin | Transient immaturity of the hepatic conjugation system in newborns | Physiological in the first days of life; pathological if early or severe |
Signs and symptoms associated with hyperbilirubinemia
Bilirubin elevation can manifest itself in different ways depending on its intensity and origin:
- Icterus: progressive yellowing of the sclera (white of the eyes), then of the skin
- Dark urine (tea or cola color): presence of direct bilirubin excreted by the kidneys
- Discolored stools (acholic, clay-colored): absence of stercobilin in case of biliary obstruction
- Generalized pruritus (itching): deposition of bile salts in the skin in cases of cholestasis
- Right abdominal or epigastric pain, depending on underlying cause
- Fatigue, nausea, loss of appetite in cases of hepatocellular damage
- Fever and chills in cases of cholangitis or infectious hepatitis
Certain presentations associated with elevated bilirubin levels constitute medical emergencies: rapidly setting jaundice with high fever and chills (Charcot triad suggestive of cholangitis), intense abdominal pain, altered general condition or mental confusion. This may be a sign of complete biliary obstruction, biliary septicemia or acute liver failure.
If these signs are present, call 911 immediately.
or go to the nearest emergency room without delay. For icterus of progressive onset without signs of severity, a prompt consultation at Clinique Omicron is recommended.
Associated additional tests
Bilirubin measurement is rarely used as a stand-alone diagnostic test. It is usually interpreted in conjunction with other tests:
- ALT, AST: liver cytolysis enzymes, elevated in cases of hepatocyte damage
- Alkaline phosphatase (ALP) and GGT: markers of cholestasis, elevated in cases of biliary obstruction
- Albumin and prothrombin time (PT/INR): reflections of hepatic synthesis function
- Complete blood count (CBC): search for underlying hemolytic anemia
- Haptoglobin, LDH, reticulocytes: hemolysis workup if indirect bilirubin predominates
- Liver serologies: HAV, HBV, HCV according to clinical and epidemiological context
- Abdominal ultrasound: the first imaging technique to visualize the liver, gallbladder and bile ducts
- MRI or cholangiography: in-depth investigation of the bile ducts in cases of suspected obstruction
Factors that can influence results
Certain situations or substances can modify the bilirubin level measured without reflecting a real pathology:
| Factor | Effect on bilirubin |
|---|---|
| Prolonged fasting | Transient elevation of indirect bilirubin, particularly in Gilbert's syndrome |
| Intense physical effort | Mild hemolysis may transiently increase indirect bilirubin levels |
| Hepatotoxic drugs | Elevation of both fractions due to hepatocellular damage or drug-induced cholestasis |
| Pregnancy (3rd trimester) | Gravidic cholestasis possible, with predominant elevation of the direct fraction |
| Light exposure | Degradation of bilirubin in the sample if the tube is not protected from light |
| Sample hemolysis | Can increase measurement bias; quality sampling is essential |
Consult at Clinique Omicron
Clinique Omicron offers prescription and interpretation of bilirubin assays as part of a complete liver workup, chronic disease follow-up or jaundice investigation, at its several points of service in Quebec. A physician or specialized nurse practitioner (SNP) can analyze your results in their overall clinical context, prescribe the appropriate complementary tests and refer you to a gastroenterologist or hepatologist if necessary. In-person and telemedicine consultations are available. To book an appointment at one of our Quebec locations, visit cliniqueomicron.ca.
The content of this page is provided for informational purposes only and is not intended to replace the advice of a qualified healthcare professional. Consult a physician for any symptoms, questions or decisions you may have regarding your health.
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