What is Bilirubin? What Does High and Low Bilirubin Mean?

What is Bilirubin? What Does High and Low Bilirubin Mean?

• Bilirubin What is bilirubin? It’s a yellowish pigment in the blood produced when old red blood cells break down and is a normal part of bile. When the liver processes bilirubin normally it leaves the body in bile and feces; if processing is impaired, bilirubin can build up in the blood and cause jaundice (yellowing of the skin and eyes). This article explains bilirubin, how it’s measured with a bilirubin test, common causes of high and low levels, normal ranges, and when to seek medical care. If you have symptoms such as yellowing of the skin, dark urine, or severe fatigue, contact your healthcare provider to discuss testing and next steps.

What is a Bilirubin Test?

A bilirubin test measures the amount of bilirubin in the blood and is commonly used to screen for and monitor liver and bile duct conditions. Bilirubin is produced during the normal breakdown of red blood cells; the liver normally processes this pigment so it can leave the body in bile. Abnormal bilirubin levels—either high or low—can point to problems such as liver disease, bile duct obstruction, or hemolytic anemia. If a routine blood test shows abnormal bilirubin levels, clinicians usually order liver enzyme tests (ALT, AST), a complete blood count, and sometimes imaging to find the cause.

• Unconjugated (indirect) bilirubin: Produced when red blood cells break down; this lipid‑soluble form is carried to the liver bound to albumin and is not yet processed for excretion.
• Conjugated (direct) bilirubin: The liver converts indirect bilirubin to a water‑soluble form (via UDP‑glucuronosyltransferase, primarily UGT1A1) so it can be excreted in bile; elevated direct bilirubin often indicates a problem with bile flow.
• Total bilirubin: The sum of direct and indirect bilirubin measured in the bloodstream; useful as a general indicator of liver and bile duct health.

What is Direct Bilirubin?

Direct (conjugated) bilirubin is the water‑soluble form made in the liver. When bile flow is blocked—for example by gallstones, strictures, or tumors—direct bilirubin can build up in the blood. Clinically this often presents as jaundice with pale stools and dark, tea‑colored urine because conjugated bilirubin is excreted in urine when levels are elevated.

What is Indirect Bilirubin?

Indirect (unconjugated) bilirubin is lipid‑soluble and is produced by the breakdown of red blood cells. It travels bound to albumin to the liver for processing. Elevated indirect bilirubin is commonly seen with increased red blood cell breakdown (hemolysis) or with conditions that reduce the liver’s ability to conjugate bilirubin, such as Gilbert’s syndrome.

What is Total Bilirubin?

Total bilirubin is the combined value of direct and indirect bilirubin in the blood. A high total bilirubin level can result from increases in either fraction, so providers use the direct/indirect split plus other tests (CBC, liver enzymes, ultrasound) to determine whether the problem is pre‑hepatic, hepatic, or post‑hepatic.

Quick examples: In hemolytic anemia, expect high indirect bilirubin with a high reticulocyte count; in obstructive jaundice (for example, a bile duct stone), expect high direct bilirubin with elevated alkaline phosphatase and abnormal ultrasound. If your bilirubin test is abnormal, ask your clinician about follow‑up tests such as ALT/AST, ALP, GGT, CBC, and abdominal imaging.

What Diseases Are Diagnosed with a Bilirubin Test?

A bilirubin test helps clinicians screen for and monitor a range of liver- and blood-related problems. Because bilirubin reflects how well the liver handles breakdown products from red blood cells, an abnormal bilirubin level prompts further testing (liver function tests such as ALT, AST, alkaline phosphatase, and GGT; CBC; and imaging) to identify the underlying cause.

• Hepatitis — viral or autoimmune inflammation of the liver that can raise bilirubin levels and cause symptoms like jaundice and fatigue.
• Cirrhosis — long-term scarring of the liver from alcohol, fatty liver, or chronic viral hepatitis; often leads to elevated bilirubin and other abnormal liver tests.
• Gallstones and bile duct obstruction — blockages that prevent bile (which contains bilirubin) from flowing out of the liver, typically causing a rise in conjugated bilirubin.
• Hemolytic anemia — any condition that causes rapid breakdown of red blood cells, increasing indirect (unconjugated) bilirubin in the blood.

Other conditions that affect bilirubin levels include inherited syndromes (for example, Gilbert’s syndrome), certain medications, and less commonly, tumors of the liver or bile ducts. If you experience symptoms such as yellowing of the skin or eyes, dark urine, pale stools, abdominal pain, or unusual fatigue, contact your healthcare provider — they may order a bilirubin test along with CBC and liver panels and recommend imaging if obstruction is suspected.

How is a Bilirubin Test Done?

Bilirubin testing can be done with a quick, minimally invasive blood draw or with a noninvasive transcutaneous screen. In newborns, clinicians commonly use a transcutaneous bilirubinometer for initial screening (a handheld device placed on the skin) and confirm results with a small heel‑prick blood sample when indicated. For adults and older children, a venous blood sample from the arm is the usual method; the lab measures total, direct (conjugated), and indirect (calculated) bilirubin.

• Screening vs diagnostic tests — transcutaneous devices give immediate screening values but serum bilirubin from blood gives the definitive measurement.
• Where and when — newborns are often screened within the first 24–48 hours and again before discharge if risk factors are present; adults have testing as part of routine blood work or when symptoms suggest liver or bile duct disease.
• Prep and results — no fasting is usually required; point‑of‑care tests and hospital labs can provide rapid results, while outpatient labs may take a day.

When to seek immediate care: in newborns, return to care quickly for poor feeding, excessive sleepiness, high-pitched crying, or rapidly rising bilirubin levels. In adults, seek urgent care for sudden jaundice, dark urine, pale stools, or severe abdominal pain. If your bilirubin test is abnormal, your provider may order follow‑up tests such as CBC, liver function tests (ALT, AST, ALP, GGT), viral hepatitis panels, or abdominal imaging.

What is the Normal Value for Bilirubin?

Total bilirubin is the combined amount of direct and indirect bilirubin measured in the blood. Typical adult laboratory reference ranges for total bilirubin are roughly 0.1–1.2 mg/dL, but exact cutoffs vary by lab and assay. Newborns normally have higher bilirubin levels because their livers are immature; some elevation is expected and monitored to prevent neonatal jaundice complications. Always confirm reference ranges and action thresholds with your laboratory or clinician.

Typical ranges by age (total bilirubin, mg/dL):

• Premature babies: higher variability; many units follow individualized charts — levels can be significantly higher than term infants and require close monitoring.
• Babies 0–7 days: newborns commonly have higher values; clinical decisions use age-in-hours nomograms (see pediatric guidance for phototherapy thresholds).
• Babies 7 days–1 month: levels usually fall as the liver matures but may still be elevated compared with adults.
• Infants 2–3 months: approach childhood-adult ranges; most infants have total bilirubin under ~2.0 mg/dL.
• Children 3 months and older and adults: typical total bilirubin is roughly 0.1–1.2 mg/dL (many labs use up to 1.3–1.4 mg/dL as the upper limit).

What the numbers mean: small, transient bilirubin elevations in newborns commonly cause physiological neonatal jaundice and often resolve without treatment. Higher levels or rapidly rising bilirubin — especially in the first 24–48 hours or when accompanied by poor feeding or lethargy — may require phototherapy or other interventions. For adults, persistent elevations warrant evaluation for liver disease, bile duct obstruction, hemolysis, or medication effects.

Practical notes: units are mg/dL in most U.S. labs; some results report μmol/L (multiply mg/dL by 17.1 to convert). If you receive abnormal bilirubin results, ask your clinician about the total bilirubin and the direct/indirect split, how the value compares to the lab reference, and what follow‑up tests (LFTs, CBC, imaging) or treatments may be needed.

What Causes High Bilirubin (Hyperbilirubinemia)?

High bilirubin, called hyperbilirubinemia, happens when the body makes too much bilirubin or the liver and bile system can’t clear it. Because bilirubin comes from the breakdown of red blood cells, abnormal levels can reflect problems with the blood, the liver, or the bile ducts. Common symptoms that suggest high bilirubin levels include jaundice (yellowing of the skin and eyes), dark urine, pale stools, and itching (pruritus).

Causes grouped by mechanism

• Pre‑hepatic (before the liver) — increased breakdown of red blood cells: Hemolytic anemia, sickle cell disease, transfusion reactions, or certain medications increase red blood cell destruction and raise indirect (unconjugated) bilirubin. Diagnostic clue: elevated reticulocyte count and anemia on CBC.
• Hepatic (within the liver) — impaired processing: Viral hepatitis, alcoholic or nonalcoholic fatty liver disease, cirrhosis, and inherited disorders such as Gilbert’s syndrome or Crigler‑Najjar syndrome reduce the liver’s ability to conjugate or excrete bilirubin. Lab pattern: mixed elevations in bilirubin with abnormal liver enzymes (ALT/AST).
• Post‑hepatic (after the liver) — obstructed bile flow: Gallstones, strictures, tumors in the bile ducts or pancreas block bile flow and cause rises in conjugated (direct) bilirubin. Typical presentation: jaundice with pale stools, dark urine, and marked alkaline phosphatase elevation; imaging (ultrasound/CT/MRCP) helps confirm obstruction.

Clinical examples: An adult with painless progressive jaundice and weight loss should prompt evaluation for obstructive causes (bile duct tumor or pancreatic cancer). A person with fatigue, pallor, and elevated indirect bilirubin likely has hemolysis and needs a CBC, reticulocyte count, and hemolysis workup.

When a clinician finds high bilirubin levels, common next tests include CBC, reticulocyte count, liver function tests (ALT, AST, ALP, GGT), direct/indirect bilirubin fractions, viral hepatitis panels, and abdominal imaging. Because high bilirubin levels can signal serious liver disease or obstructive conditions, rapidly rising bilirubin or severe symptoms (fever, severe abdominal pain, confusion, very high bilirubin) warrant urgent evaluation.

What Causes Low Bilirubin (Hypobilirubinemia)?

Low bilirubin (hypobilirubinemia) is uncommon and usually not harmful. Mildly low values are often incidental findings on routine blood work and typically do not indicate a health problem. In some cases, certain medications or increased clearance of bilirubin can lower measured bilirubin levels — however, evidence for specific drug effects varies and should be interpreted with caution.

When to investigate: persistent or unexplained low bilirubin accompanied by other abnormal lab results or clinical symptoms (for example, unexplained fatigue, signs of liver dysfunction, or unusual lab patterns) may prompt further evaluation. Depending on the context, a clinician might review medications, repeat the test, and check liver panels and other relevant studies.

If you are concerned about a low bilirubin result, discuss it with your healthcare provider. They can put the value into context with your overall health, medications, and other blood test results and decide whether any follow-up is needed.

Frequently Asked Questions About Bilirubin Testing

Key takeaways: Bilirubin is a pigment produced from red blood cell breakdown; high bilirubin often causes jaundice and may signal hemolysis, liver disease, or bile duct obstruction. Newborns commonly have higher bilirubin and are routinely screened. Seek prompt care for rapidly rising levels or warning signs such as poor feeding, extreme sleepiness, or very dark urine.

What are the causes of low bilirubin?

Low bilirubin levels are uncommon and usually not clinically important. Occasional low values are found on routine blood tests and most often require no action. In some cases, certain medications or laboratory variation can lower measured bilirubin; persistent unexplained low values with other abnormal tests should prompt review by your clinician.

What are the causes of high bilirubin?

High bilirubin can result from increased red blood cell breakdown (pre‑hepatic), impaired liver processing (hepatic), or blocked bile flow (post‑hepatic). Common causes include hemolytic anemia, viral hepatitis, cirrhosis, gallstones or bile duct obstruction, and inherited syndromes such as Gilbert’s, Rotor, or Dubin‑Johnson. Medications and serious illnesses can also affect bilirubin.

In what cases is elevated bilirubin seen?

Elevated bilirubin is seen with hemolysis (increased breakdown of red blood cells), disorders that impair the liver’s ability to conjugate or excrete bilirubin, and obstructive processes that block bile flow. Lab patterns (direct vs indirect bilirubin, plus liver enzymes and CBC) help determine the likely cause.

What is high bilirubin?

High bilirubin levels (hyperbilirubinemia) commonly cause jaundice — yellowing of the skin and eyes — and may be accompanied by dark urine, pale stools, or itching. High bilirubin can reflect rapid red blood cell destruction or liver and bile duct problems; evaluation usually includes liver function tests, CBC, and imaging when obstruction is suspected.

What is low bilirubin?

Low bilirubin is typically an incidental, benign finding and rarely needs treatment. If low bilirubin appears alongside other abnormal results or symptoms, your clinician may repeat the test and review medications and clinical history.

What is jaundice?

Jaundice is the yellowing of the skin and eyes caused by elevated bilirubin in the blood. It can occur in adults and newborns and signals that bilirubin levels or liver/bile function should be evaluated.

What are the causes of jaundice?

Jaundice can be caused by high bilirubin due to hemolysis, liver diseases (viral hepatitis, cirrhosis), obstructive conditions (gallstones, bile duct tumors), newborn physiological immaturity, or certain genetic syndromes. The pattern of direct vs indirect bilirubin and additional tests help pinpoint the cause.

What are the symptoms of jaundice?

The most obvious symptom is yellowing of the skin and eyes. Other possible symptoms include itching, abdominal pain, pale stools, dark urine, fever, weight loss, poor feeding (in newborns), lethargy, and confusion in severe cases.

How is jaundice treated?

Treatment targets the underlying cause: hemolysis is managed by treating the anemia, obstructive causes may require endoscopic or surgical procedures to relieve blockage, and liver disease treatment depends on the specific diagnosis. In newborns, phototherapy (light therapy) helps break down excess bilirubin; severe neonatal cases may need additional interventions such as exchange transfusion.

How long does jaundice last in adults?

Duration depends on the cause. Jaundice from transient illnesses or drug reactions may resolve in weeks once the cause is treated, while chronic liver disease–related jaundice may persist or fluctuate and requires long‑term management.

What is jaundice in newborn babies?

Neonatal jaundice is common because a newborn’s liver is still maturing. Most cases are physiological and resolve as the liver matures, but some require monitoring and treatment to prevent complications.

How long does prolonged jaundice last?

Prolonged jaundice in newborns is generally defined as jaundice lasting more than two weeks in full‑term infants or more than three weeks in preterm infants. Prolonged jaundice requires evaluation to rule out underlying liver or metabolic conditions.

What is breast milk jaundice?

Breast milk jaundice describes a benign, usually late‑onset rise in bilirubin associated with breastfeeding. It can persist for several weeks but typically does not require stopping breastfeeding; clinicians monitor levels and treat if thresholds for phototherapy are reached.

What are the symptoms of jaundice in newborn babies?

Look for yellowing of the skin and eyes, increased sleepiness, difficulty feeding, and changes in stool and urine color. Red‑flag symptoms that need immediate medical attention include poor feeding, excessive lethargy, high‑pitched crying, arching, or signs of dehydration.

How is jaundice treated in newborn babies?

Initial treatment often includes frequent breastfeeding and phototherapy, which uses light to convert bilirubin into forms the body can excrete. In severe or rapidly rising cases, more intensive measures such as IV fluids or exchange transfusion may be required. Always follow your pediatrician’s guidance and hospital protocols.

What is kernicterus?

Kernicterus is a rare but serious complication that occurs when very high bilirubin levels cross into the newborn brain, potentially causing permanent neurologic impairment. Modern screening and treatment have made kernicterus uncommon; prompt recognition and treatment of high bilirubin in newborns are critical to prevention.

If you’re concerned about bilirubin results: contact your healthcare provider. For newborns, return for immediate evaluation if feeding problems, extreme sleepiness, or rapidly increasing yellowing occur. For adults, seek care for sudden jaundice, severe abdominal pain, fever, or confusion. Your provider will interpret bilirubin numbers with other tests and recommend appropriate follow‑up or treatment.