The essentials

Indirect (unconjugated) bilirubin is the yellow pigment from old red blood cells before the liver processes it. It is usually calculated as total minus direct bilirubin. A mildly high value with normal liver enzymes and a normal blood count is most often Gilbert syndrome, which is harmless. Faster breakdown of red blood cells (hemolysis) and some medicines are the other main causes, and a few simple blood tests tell them apart.

How do I read indirect bilirubin on my lab report?

Bilirubin comes in two forms. The form made from old red blood cells is not water-soluble and travels to the liver bound to a protein called albumin: this is unconjugated, or indirect, bilirubin. The liver attaches a sugar to it, making conjugated, or direct, bilirubin, which leaves the body in bile[4][6]. Most labs do not measure the indirect form: they subtract direct from total bilirubin[3][4].

Fictitious example of a lab report line (United States format)
TestResultReference rangeFlag
Bilirubin, Total2.1 mg/dL0.1-1.2 mg/dLH
Bilirubin, Direct0.2 mg/dL<0.3 mg/dL-
Bilirubin, Indirect (calculated)1.9 mg/dL0.2-0.8 mg/dLH
  1. Total bilirubin: both forms together. Here it is high, so the lab or your clinician looks at the split[7].
  2. Direct bilirubin: normal. A high direct value would point toward the liver or bile ducts instead[7].
  3. Indirect bilirubin (calculated): 2.1 minus 0.2 gives 1.9 mg/dL. Direct bilirubin is under 20% of the total, the pattern called unconjugated hyperbilirubinemia[5].
  4. Flag H: above this lab's range. It describes the number, not a diagnosis: the next step is to look at your liver enzymes and blood count.

An H next to indirect bilirubin but a normal direct value? BloodSense reads your whole report, line by line, and shows how bilirubin fits with your liver enzymes and blood count.

Get my bilirubin result explained

Why is indirect bilirubin checked?

Bilirubin is tested to look for the cause of jaundice (yellow skin or eyes), to check the liver, to follow a known liver disease, and to look for red blood cells breaking down too fast[1]. When total bilirubin comes back high, for example on a comprehensive metabolic panel, the American College of Gastroenterology recommends splitting it into direct and indirect fractions, because the two point to different problems[7]. The general meaning of a high total is covered in our page on total bilirubin results; this page focuses on the indirect fraction.

What is the normal range for indirect bilirubin?

Ranges vary slightly between labs, and many reports print no range for the indirect line because it is calculated. Values are in mg/dL in the United States; multiply by 17.1 to get µmol/L, the unit used in many other countries[5].

Adult reference ranges for bilirubin fractions
Fractionmg/dLµmol/LSource
Indirect (unconjugated)0.2-0.83.4-13.7University of Rochester Medical Center[3]
Indirect (unconjugated)0.2-0.73.4-12.0Reference range shown in a JAMA case report[5]
Direct (conjugated)less than 0.3less than 5.1MedlinePlus[2]
Total0.1-1.21.71-20.5MedlinePlus[2]
Total0.2-1.33.4-22.2Cleveland Clinic[4]

Your laboratory's range prevails. Yellowing of the skin or eyes usually becomes visible once total bilirubin reaches about 2 to 3 mg/dL[2][6]. Newborns are different: their bilirubin is higher in the first days of life and is judged against the baby's age in hours[2][11].

What causes high indirect bilirubin?

Indirect bilirubin rises when the body makes more bilirubin than the liver can handle, when the liver takes it up more slowly, or when the conjugation step is slowed[5][6].

  • Common Gilbert syndrome: an inherited, harmless slowdown of the enzyme that conjugates bilirubin, found in about 3 to 7% of Americans[8]. The total usually stays under 5 mg/dL, direct bilirubin stays under 20% of the total, and it often goes up with fasting, infection or overexertion[5]. About 30% of people with it have no symptoms and find out from a routine test[8].
  • Possible Hemolysis, red blood cells destroyed faster than normal: autoimmune hemolytic anemia, sickle cell disease, thalassemia, G6PD deficiency or hereditary spherocytosis[6][9]. A reaction to a blood transfusion can do the same[2].
  • Possible Medicines that reduce bilirubin uptake or conjugation, such as gemfibrozil, irinotecan and the HIV medicines atazanavir and indinavir[5]. With atazanavir, the rise is expected; the chance of jaundice that leads people to stop it is highest in those with two copies of the Gilbert gene variant[10].
  • Possible Internal bleeding, and vigorous exercise before the draw[3].
  • Possible Newborn jaundice, because a baby's liver is not yet mature enough to clear bilirubin; it usually clears within a few weeks[1].
  • Rare Crigler-Najjar syndrome, a much more severe inherited deficiency of the same enzyme[6], and some bone marrow disorders such as polycythemia vera[6].

A low indirect bilirubin is not usually a cause for concern[1].

Is it Gilbert syndrome or hemolysis? How the other tests help

Doctors rarely read indirect bilirubin alone. The diagnosis of Gilbert syndrome is made only after liver and blood disorders have been excluded[5]. Hemolysis is checked with a blood smear, LDH and haptoglobin[5], together with the complete blood count and reticulocyte count[9].

Common result patterns with a high indirect bilirubin
Other resultsWhat it suggests
Normal hemoglobin, haptoglobin and LDH; normal ALT, AST and alkaline phosphatase; no culprit medicineGilbert syndrome is the most likely cause[5]
Low hemoglobin, high reticulocytes, low haptoglobin, high LDHRed blood cells breaking down faster than normal; a Coombs test may look for an immune cause[9]
Direct bilirubin also high, with high ALT or alkaline phosphataseA liver or bile duct problem; see direct bilirubin results[7]

If everything except bilirubin stays normal over the next 12 months, Gilbert syndrome can be diagnosed. Fasting "provocation" tests are not recommended, and genetic testing is rarely needed, for example when the total stays above 5 mg/dL[5]. Indirect bilirubin is not water-soluble, so it does not pass into urine, and a urine bilirubin test is usually negative in these cases[4].

What can affect an indirect bilirubin result before the blood draw?

Your provider may ask you to fast for several hours, and many medicines change bilirubin levels[1][2]. In Gilbert syndrome, skipping meals or a recent illness can push the value up[5]. Before the draw, check this list:

  • Ask whether you need to fast, and for how long (see fasting before a blood test).
  • Avoid an intense workout the day before[3].
  • Bring a list of all medicines and supplements; do not stop any without advice[1].
  • Mention a recent infection, a long fast or a large bruise.
  • For a repeat test, try to use the same lab so the ranges match.

When should I see a doctor about high indirect bilirubin?

When to see a doctor

  • Emergency: call 911 if yellowing comes with confusion or unusual sleepiness, vomiting blood, black stools, severe abdominal pain, or shortness of breath and fainting. For a newborn, call 911 if the baby is very hard to wake, will not feed, or has a high-pitched cry or arched back.
  • Within 24 to 48 hours if yellow eyes or skin are new, if you also have dark urine, pale stools or itching, or if you feel very tired and short of breath, which can come with anemia. Newborns with jaundice should be checked promptly as advised by their pediatrician[11].
  • At your next appointment if you feel well and only indirect bilirubin is mildly high, with a normal direct value, normal liver enzymes and a normal blood count.

Questions to ask your doctor

  1. Is my bilirubin mainly indirect, and what share of the total is direct?
  2. Are my liver enzymes and blood count normal?
  3. Do I need haptoglobin, LDH or a reticulocyte count to rule out hemolysis?
  4. Could one of my medicines explain the result?
  5. When should I repeat the test, and does Gilbert syndrome fit my results?

Frequently asked questions

Is high indirect bilirubin dangerous?

Usually not in adults. A mild rise with otherwise normal tests is most often Gilbert syndrome, which needs no treatment[5]. The concern depends on the cause: hemolysis needs a diagnosis, and very high levels in newborns can harm the brain, which is why babies are monitored closely[11].

Can stress or fasting raise indirect bilirubin?

In Gilbert syndrome, yes: fasting, infection and overexertion are known triggers[5], and physical or emotional stress can make it worse[6].

Why does my report show no range for indirect bilirubin?

Because the value is calculated, not measured[4]. Read it against the total and direct lines, and ask your lab for its range if needed.

Does high indirect bilirubin mean liver damage?

Not necessarily. It is a high conjugated (direct) bilirubin that implies liver disease or a bile duct blockage in most settings[7]. A raised indirect fraction more often reflects Gilbert syndrome or hemolysis[5][6].

  1. MedlinePlus. Bilirubin Blood Test. US National Library of Medicine. medlineplus.gov (accessed November 2, 2026)
  2. MedlinePlus Medical Encyclopedia. Bilirubin blood test. US National Library of Medicine. medlineplus.gov (accessed November 2, 2026)
  3. University of Rochester Medical Center Health Encyclopedia. Indirect Bilirubin. urmc.rochester.edu (accessed November 2, 2026)
  4. Cleveland Clinic. Bilirubin Test: Understanding High vs. Low Levels & Causes. Updated January 9, 2023. my.clevelandclinic.org (accessed November 2, 2026)
  5. VanWagner LB, Green RM. Evaluating elevated bilirubin levels in asymptomatic adults. JAMA. 2015;313(5):516-517. doi:10.1001/jama.2014.12835 (accessed November 2, 2026)
  6. Fargo MV, Grogan SP, Saguil A. Evaluation of jaundice in adults. Am Fam Physician. 2017;95(3):164-168. aafp.org (accessed November 2, 2026)
  7. Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: Evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18-35. doi:10.1038/ajg.2016.517 (accessed November 2, 2026)
  8. MedlinePlus Genetics. Gilbert syndrome. US National Library of Medicine. medlineplus.gov (accessed November 2, 2026)
  9. MedlinePlus Medical Encyclopedia. Hemolytic anemia. US National Library of Medicine. medlineplus.gov (accessed November 2, 2026)
  10. Gammal RS, Court MH, Haidar CE, et al. Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for UGT1A1 and atazanavir prescribing. Clin Pharmacol Ther. 2016;99(4):363-369. doi:10.1002/cpt.269 (accessed November 2, 2026)
  11. Kemper AR, Newman TB, Slaughter JL, et al. Clinical practice guideline revision: management of hyperbilirubinemia in the newborn infant 35 or more weeks of gestation. Pediatrics. 2022;150(3):e2022058859. doi:10.1542/peds.2022-058859 (accessed November 2, 2026)
  12. Labcorp. Bilirubin, Total and Direct (test 001214). labcorp.com (accessed November 2, 2026)

This page is general information. It does not replace the advice of a doctor, who interprets your results with your symptoms, history and examination.