- 01Gilbert's is read from a pattern across tests
A high total bilirubin on its own cannot tell Gilbert's syndrome apart from liver disease or red cells breaking down. Gilbert's fits only when the raised part is indirect (unconjugated) bilirubin, direct bilirubin is normal, the liver enzymes are normal and the blood count shows no hemolysis 3. A raised direct bilirubin, abnormal enzymes or dark urine means something else is going on, even in someone already labeled with Gilbert's.
A total bilirubin of 1.6 or 2.1 mg/dL with everything else on the panel normal is most often Gilbert's syndrome, a harmless inherited trait that 3 to 7 percent of people in the United States have; about 30 percent of them never notice a symptom 1. It fits only when the numbers follow one pattern, set out below with the tests that confirm it and the signs that mean something else.
What Gilbert's syndrome is
Gilbert's syndrome is an inherited difference in how the liver handles bilirubin, the yellow pigment made when old red blood cells are broken down. Red cells are retired every day, so bilirubin is produced all the time. Before the body can get rid of bilirubin, the liver has to attach sugar molecules to it (a step called conjugation), which makes it water-soluble so it can leave in bile. The enzyme that does this is called UGT1A1. In Gilbert's syndrome, UGT1A1 works at about 30 percent of its normal rate, so unconjugated bilirubin backs up in the blood 1.
How bilirubin is made and cleared, and where Gilbert's slows it
Gilbert's syndrome is usually noticed after puberty, when hormone changes slow bilirubin handling further 2. It is diagnosed more often in men, and the NHS notes it is also more common in people with type 1 diabetes 5.
Gilbert's syndrome is a common genetic condition that may cause mild jaundice. It does not usually need any treatment.NHS, Gilbert's syndrome (reviewed August 2025) 5
Gilbert's syndrome symptoms: what it feels like
The main sign of Gilbert's syndrome is mild jaundice: a yellow tinge to the whites of the eyes, and less often the skin, that comes for a few days and fades. Yellowing of the skin may be less noticeable on brown or black skin, so the whites of the eyes are the better place to look 5. Many people with Gilbert's syndrome see no yellowing at all and only know about it from a blood test 1.
Visible episodes tend to follow a trigger that raises bilirubin for a day or two. The common triggers are:
- Fasting, skipped meals or a very low-calorie diet
- Dehydration
- Infections, including a cold or stomach bug
- Hard or prolonged exercise
- Poor sleep and stress
- Menstrual periods
- Alcohol, for some people 5
Some people with Gilbert's syndrome report tiredness, nausea, poor concentration or stomach discomfort. These symptoms have not been shown to come from the slightly raised bilirubin. Tiredness that lasts deserves its own look, because common causes such as low iron or an underactive thyroid can sit alongside Gilbert's and be missed if everything is blamed on it. Our guide to <a href="/symptoms/fatigue">fatigue</a> covers the tests that check those causes.
What Gilbert's syndrome does not cause
Gilbert's syndrome raises only unconjugated bilirubin, which is bound to albumin and is not filtered into urine. So it does not make urine dark, does not put bilirubin on a <a href="/biomarkers/urine-bilirubin">urine dipstick</a>, and does not make stools pale 4. It also does not cause itching, ongoing pain or liver damage. Jaundice with dark urine, pale or clay-colored stools, itching or fever points to the liver or bile ducts and needs same-day care, even if you were told years ago that you have Gilbert's.
Gilbert's syndrome bilirubin levels: what the numbers look like
An adult reference range for total bilirubin is about 0.1 to 1.2 mg/dL, or about 2 to 21 µmol/L; labs vary slightly. In Gilbert's syndrome, total bilirubin is mildly raised, usually under 3 mg/dL (51 µmol/L) and most often 1.2 to 2 mg/dL (21 to 34 µmol/L), with direct bilirubin in the normal range 2. The level moves from week to week, and fasting can raise it two- to threefold 2. To convert, multiply mg/dL by 17.1 to get µmol/L, or divide µmol/L by 17.1 to get mg/dL.
Total bilirubin: an example resultmg/dL
| Total bilirubin | In µmol/L | How it fits Gilbert's syndrome | What to check |
|---|---|---|---|
| Up to 1.2 mg/dL | Up to about 21 | Normal range; people with Gilbert's often read here between episodes | Nothing extra if the rest of the panel is normal |
| 1.2 to 2 mg/dL | About 21 to 34 | The most common Gilbert's range 2 | Direct bilirubin, liver enzymes (ALT, AST, ALP, GGT) and a full blood count |
| 2 to 3 mg/dL | About 34 to 51 | Seen in Gilbert's, usually after fasting, illness or hard exercise | The same tests, plus a repeat after normal eating |
| Above 3 mg/dL | Above about 51 | Less typical; raises the question of hemolysis or liver disease | Tests for red cell breakdown (reticulocytes, haptoglobin and LDH, explained below) and a clinician's review |
The bilirubin results to read together
How doctors confirm Gilbert's syndrome
Gilbert's syndrome is diagnosed by exclusion: a clinician confirms the pattern and rules out the conditions that look similar. The American College of Gastroenterology guideline advises splitting a raised total bilirubin into its direct and indirect parts first. An isolated rise in indirect bilirubin, with normal liver enzymes and no hemolysis (red cells breaking down early), is most often Gilbert's syndrome, while a raised direct bilirubin points to liver or bile duct disease 3.
- 1Split the bilirubinDirect and indirect bilirubin are measured. In Gilbert's syndrome, direct bilirubin is normal and most of the total is indirect 3.
- 2Check the liver enzymesALT, AST, ALP (alkaline phosphatase) and GGT should be normal. Our guide to <a href="/learn/liver-enzymes-explained">liver enzymes</a> explains what each one tracks.
- 3Rule out hemolysisA normal hemoglobin, normal reticulocyte count (young red cells), normal haptoglobin and normal LDH (lactate dehydrogenase) make red cell breakdown unlikely 2 4. The <a href="/learn/cbc-explained">blood count guide</a> covers the first two.
- 4Repeat if neededA doctor may repeat the test, or occasionally arrange one after 24 to 48 hours of reduced calories, to show the typical rise; this is rarely needed today. A genetic test for UGT1A1 is available but also rarely needed 2.
The tests that rule out the look-alikes
Gilbert's, hemolysis, liver disease or Crigler-Najjar?
Four conditions can raise bilirubin, and the pattern across tests separates them 2 4. Crigler-Najjar syndrome comes from more severe changes in the same UGT1A1 gene: type 1 leaves almost no enzyme activity and type 2 less than about 10 percent, with bilirubin many times higher than in Gilbert's 2.
| Gilbert's syndrome | Hemolysis | Liver or bile duct disease | Crigler-Najjar | |
|---|---|---|---|---|
| Which bilirubin rises | Indirect | Indirect | Direct (often both) | Indirect |
| Typical total bilirubin | Usually under 3 mg/dL, most often 1.2 to 2 | Usually under about 4 to 5 mg/dL | Any level, can be high | Type 2: about 6 to 20 mg/dL; type 1: higher, from birth |
| Liver enzymes | Normal | Usually normal; LDH high, AST may be mildly raised | Often abnormal | Normal |
| Hemoglobin, reticulocytes, haptoglobin | Normal | Low hemoglobin, high reticulocytes, low haptoglobin | Usually normal | Normal |
| Urine | Normal color | Normal color | Can be dark | Normal color |
| How serious | Harmless | Depends on the cause | Needs prompt assessment | Serious; type 1 needs specialist care |
For more on the hemolysis side, see <a href="/conditions/anemia">anemia</a> and <a href="/biomarkers/ldh/high">a high LDH</a>. For the most common liver cause of abnormal enzymes, see <a href="/conditions/fatty-liver">fatty liver</a>.
When a high bilirubin is not Gilbert's syndrome
A Gilbert's label from years ago covers the old pattern only. A new result needs a fresh look if it shows a raised direct bilirubin, abnormal ALT, <a href="/biomarkers/ast/high">AST</a>, <a href="/biomarkers/alp/high">ALP</a> or GGT, anemia or a high reticulocyte count, or a bilirubin that is well above your usual level or rising on each test. The <a href="/biomarkers/total-bilirubin/high">high bilirubin page</a> walks through the other causes.
Is Gilbert's syndrome genetic? One copy, two copies, and your children
Gilbert's syndrome is genetic and is present from birth. Alcohol, diet and lifestyle do not cause it. The most common cause is a variant called UGT1A1*28: an extra pair of letters (TA) in the switch region that controls the UGT1A1 gene, so the liver makes less of the enzyme. This variant is uncommon in Asian populations, where Gilbert's more often comes from a single-letter change inside the gene itself, such as the one known as G71R or UGT1A1*6 1 2.
With UGT1A1*28, Gilbert's syndrome usually needs two copies of the variant, one from each parent; with the single-letter changes, one copy can be enough 1. Not everyone with two copies of UGT1A1*28 has a raised bilirubin, because red cell turnover, hormones and other genes also set the level. The table gives the plain odds for each child under the usual UGT1A1*28 pattern.
| Parents | Chance a child has two copies (Gilbert's genotype) | Chance a child has one copy |
|---|---|---|
| Both parents carry one copy | 1 in 4 | 1 in 2 |
| One parent has Gilbert's (two copies), the other has none | None | Every child |
| One parent has Gilbert's, the other carries one copy | 1 in 2 | 1 in 2 |
| Both parents have Gilbert's | Every child | None |
Every child of a parent with Gilbert's syndrome inherits at least one copy of the variant, and whether they have Gilbert's depends on the other parent's genes. A child who inherits it lives with the same harmless trait.
Medicines and Gilbert's syndrome
UGT1A1 also clears some medicines, so a slower enzyme can mean higher drug levels. Two matter most:
- Irinotecan, a chemotherapy drug. People with two copies of UGT1A1*28 have a higher risk of a severe drop in white blood cells (neutropenia), and the drug label advises the oncologist to consider a lower starting dose 7.
- Atazanavir, an HIV drug. It blocks UGT1A1 and raises indirect bilirubin, and jaundice that leads people to stop it is more likely with two reduced-function copies 8.
For everyday medicines, the NHS says people with Gilbert's syndrome may need closer monitoring on some drugs, such as <a href="/compounds/statins">statins</a> for high cholesterol, and advises speaking to a GP or pharmacist before taking any new medicine 5. Tell every prescriber and pharmacist about the diagnosis so they can check what applies to you.
Is Gilbert's syndrome serious? Life expectancy and the possible upside
Gilbert's syndrome is not serious. It does not damage the liver, does not lead to cirrhosis and does not affect how long you live 5. The one known downside is a slightly higher risk of gallstones 5.
Bilirubin is also an antioxidant, and mildly higher levels have been linked with less heart disease. In a Czech study, ischemic heart disease was found in 2 percent of people over 45 with Gilbert's syndrome, against 12 percent of the general population of the same age 6. That is an association from an observational study and does not prove that bilirubin protects the heart.
Living with Gilbert's syndrome: food, alcohol, exercise and pregnancy
Gilbert's syndrome needs no treatment and no special diet 5. If visible yellowing bothers you, regular meals and enough fluid help keep bilirubin closer to its baseline, because fasting and dehydration are the triggers people can control most easily.
CalculatorWater intake calculatorDehydration is one of the common triggers for a visible Gilbert's episode.Work it out Alcohol does not cause Gilbert's syndrome, but some people notice that drinking brings on an episode, so keeping a note of what came before each episode is useful 5. Alcohol also moves GGT and other liver results; our guide to <a href="/learn/alcohol-and-blood-tests">alcohol and blood tests</a> covers how. Exercise is fine, though very hard sessions can raise bilirubin for a day. Gilbert's syndrome is not known to cause problems in pregnancy; mention it to your midwife or obstetrician so a raised bilirubin on routine bloods is read in context.
No supplement is needed for Gilbert's syndrome, and none changes how UGT1A1 works. Milk thistle is often sold for the liver, but it has not been shown to change Gilbert's; the <a href="/supplements-for/liver-health">liver health page</a> sets out where it and others have evidence.
Tracking your bilirubin over time
Because bilirubin in Gilbert's syndrome swings with food, sleep and illness, a run of results tells you more than any single one. Line up your total bilirubin with direct bilirubin, ALT and GGT from each test: in Gilbert's syndrome, total bilirubin moves up and down while the other three stay flat. A steady climb, or any change in the other three, is the signal to take back to a doctor. Our guide on <a href="/learn/trends-beat-single-readings">why trends beat single readings</a> explains how to compare results fairly.
When to see a doctor
Not sure which tests your panel already has? <a href="/learn/what-blood-tests-should-i-get">What blood tests should I get</a> sets out the standard panels.
Gilbert's syndrome is diagnosed by a clinician after other causes of a high bilirubin are ruled out; do not assume a yellow tinge is Gilbert's if it is new to you. Get same-day care for yellow skin or eyes with dark urine, pale stools, fever, abdominal pain, itching, confusion or vomiting, and tell every prescriber and pharmacist about the diagnosis, especially before irinotecan or atazanavir.
Citations
- MedlinePlus Genetics. Gilbert syndrome. National Library of Medicine
- Grant LM, Faust TW, Thoguluva Chandrasekar V, John S. Gilbert Syndrome. StatPearls (2024)
- Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. Am J Gastroenterol (2017);112:18-35
- Fargo MV, Grogan SP, Saguil A. Evaluation of Jaundice in Adults. Am Fam Physician (2017);95(3):164-168
- NHS. Gilbert's syndrome (reviewed August 2025)
- Vitek L, Jirsa M, Brodanova M, et al. Gilbert syndrome and ischemic heart disease: a protective effect of elevated bilirubin levels. Atherosclerosis (2002);160(2):449-456
- Dean L. Irinotecan Therapy and UGT1A1 Genotype. Medical Genetics Summaries, National Center for Biotechnology Information
- 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
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
