Isolated hyperbilirubinaemia and bilirubin disorders

• Bilirubin is made when old red blood cells are broken down. It is carried to the liver, conjugated with glucuronic acid, and excreted into bile; the bowel converts it to the brown pigments you see in stool.
• An isolated rise in bilirubin with otherwise normal liver tests means no hepatocellular injury and no cholestasis. The question is whether the bilirubin is unconjugated (overproduction or a conjugation defect) or conjugated (an excretion defect).
• The commonest inherited cause is Gilbert syndrome, which affects roughly 3 to 12 percent of people. It is benign, needs no treatment, and gives an unconjugated bilirubin that usually stays below 85.5 micromol/L, rising with fasting, illness, dehydration or stress.
• Crigler-Najjar is the severe end of the same UGT1A1 spectrum: type 1 has no enzyme activity, enormous bilirubin levels from birth, and a real risk of kernicterus; type 2 has some activity and responds to phenobarbital.
• Dubin-Johnson and Rotor are autosomal recessive conjugated hyperbilirubinaemias in people who are otherwise well. Dubin-Johnson leaves a black liver and a markedly raised urinary coproporphyrin I fraction; Rotor leaves a normal liver and a milder coproporphyrin pattern.

By the end of this page you should be able to:

1. Draw, in words, the pathway from haem breakdown to stercobilin, naming the enzymes and transporters.
2. Take a patient with an isolated high bilirubin and decide whether it is unconjugated or conjugated, and what to check next.
3. Recognise Gilbert syndrome, state why it is benign, and distinguish it from haemolysis.
4. Compare Crigler-Najjar types 1 and 2 on enzyme activity, bilirubin level, and treatment.
5. Compare Dubin-Johnson and Rotor syndrome on liver appearance, inheritance, and urinary coproporphyrin.
6. Outline the workup of haemolysis with the expected results.
7. Explain in one breath why a newborn with direct hyperbilirubinaemia is an emergency.

Bilirubin is often split into "indirect" (unconjugated) and "direct" (conjugated) fractions. Unconjugated bilirubin is lipid soluble and bound to albumin in plasma; conjugated bilirubin is water soluble and can appear in urine. That single distinction organises almost everything that follows.

Gilbert syndrome is common. Population estimates run from 3 to 12 percent, with the highest rates (15 to 25 percent) in people of African ancestry and lower rates (2 to 10 percent) in Caucasians. It usually declares itself in adolescence, and men outnumber women by roughly 1.5 to 10 to 1. ^[1]

Crigler-Najjar is extremely rare, with a worldwide estimate of fewer than one in 0.75 million to one in 1.0 million live births. There are real regional differences: the expert consensus on which this page leans puts the European figure below one in 0.1 million live births. ^[1]

Dubin-Johnson and Rotor syndromes are also rare, with no exact incidence settled in the open-access literature; both are reported worldwide and both follow autosomal recessive inheritance (Rotor with digenic involvement of SLCO1B1 and SLCO1B3). ^[1][2]

By fraction, the inherited disorders split cleanly:

• Unconjugated hyperbilirubinaemia: Gilbert (mild), Crigler-Najjar types 1 and 2 (severe).
• Conjugated hyperbilirubinaemia: Dubin-Johnson and Rotor (both benign).

Haemolysis of any kind belongs to the first group, because haem breakdown makes bilirubin faster than the liver can conjugate it. That is why every isolated unconjugated rise must be asked "is the bone marrow being asked to replace lost red cells?"

There are no modifiable risk factors for these inherited syndromes; the "risk" is being born with the genotype. The important practical risks are secondary:

• Inter-current illness, fasting, dehydration, exertion, menstruation and psychological stress all raise unconjugated bilirubin in Gilbert syndrome, which is why jaundice appears during flu, examinations or a Ramadan fast. ^[1]
• For Crigler-Najjar type 2, trauma, surgery or inter-current illness can precipitate an adult-onset encephalopathy. The risk becomes significant once the bilirubin-to-albumin molar ratio exceeds 0.8 (calculated as [bilirubin (mg/dL) x 17.1] / [albumin (g/dL) x 151]). ^[1]
• Standard prescribing (contraceptives, some chemotherapy, antiretroviral protease inhibitors) can unmask a Gilbert genotype by interfering with UGT1A1.
• For Dubin-Johnson and Rotor, most people are found by accident when a routine test shows a raised direct bilirubin; no trigger is needed.

The pathway has five jobs: make the bilirubin, carry it, take it up, conjugate it, and excrete it. Errors at each stage give the syndromes in this topic.

Why the unconjugated form is dangerous. Unconjugated bilirubin is lipophilic. In the newborn, the blood-brain barrier is incompletely developed, so a high unconjugated level crosses into brain tissue and deposits in the basal ganglia and brainstem nuclei, producing acute bilirubin encephalopathy and, if unchecked, chronic bilirubin encephalopathy (kernicterus).

Enterohepatic circulation. In the gut, most conjugated bilirubin is converted to stercobilin and excreted in stool; some is deconjugated by bacterial enzymes and reabsorbed as urobilinogen, which the kidney clears into urine. Newborns have poor gut flora and a long gut transit, so deconjugation and reabsorption are increased; that is one reason neonatal jaundice is common. Urine normally contains some urobilinogen; it contains no bilirubin unless the serum conjugated fraction is high.

The single pivotal question is whether the raised bilirubin is unconjugated or conjugated. The rest of the workup follows from that.

A diagnostic rule worth remembering: unconjugated hyperbilirubinaemia with a normal physical examination and normal blood count in an adolescent or young adult is, in most cases, Gilbert syndrome. The traps are missing a simultaneous haemolysis (hereditary spherocytosis, autoimmune haemolysis) and attributing a drug-induced cholestasis to an inherited syndrome.

Gilbert syndrome is caused by variants in UGT1A1 that reduce enzyme activity to about 30 percent of normal, not abolish it. The TATA-box insertion A(TA)7TAA (UGT1A1*28) is the classic variant in white populations; other common variants (c.211G>A, c. -3275T>G) matter more in East Asian populations. It is inherited in an autosomal recessive fashion, or behaves recessively when it relies on homozygosity of these common promoter or enhancer variants. ^[1]

Clinical picture. Most people are found incidentally on a screening test or when they turn yellow during a viral illness. Total bilirubin usually sits between 17.1 and 102.6 micromol/L, the majority under 85.5 micromol/L, and the predominant fraction is unconjugated. There is no hepatosplenomegaly, no abdominal pain, no pruritus, and the rest of the liver panel is normal. Episodes of visible jaundice are triggered by fasting, dehydration, exertion, psychological stress, inter-current illness, alcohol excess and menstruation. ^[1]

A positive family history of jaundice is common, and the onset is typically in adolescence rather than infancy.

Diagnosis. Exclusion plus time. A clinical diagnosis can be made when at least two serum total bilirubin measurements, each above the upper limit of normal (17.1 to 102.6 micromol/L), are recorded more than six months apart, with normal ALT, AST, alkaline phosphatase and gamma-glutamyltransferase and after haemolysis has been excluded. ^[1] Genetic testing for UGT1A1 variants confirms it and is particularly useful in atypical cases.

Haemolysis must be excluded first. In Gilbert syndrome the red cell count, haemoglobin and haematocrit are normal or only mildly changed, the reticulocyte percentage is usually below 1.5 percent, the blood film looks normal, and the Coombs test is negative. Lactate dehydrogenase and haptoglobin sit in their normal ranges. ^[1]

Management. None is required. The condition is benign: there is no progression to fibrosis or cirrhosis, no excess mortality, and no treatment needed even during pregnancy. When jaundice itself is cosmetically troubling, reassurance and avoidance of the triggering factor are the whole treatment. If a bilirubin surge is provoked by a serious illness, treat the illness. Phenobarbital is not needed for Gilbert syndrome; when jaundice significantly impairs quality of life, 30 to 60 mg a day at bedtime can be used. ^[1]

Crigler-Najjar is the severe end of the UGT1A1 spectrum. The same single gene goes from "about 30 percent activity" (Gilbert) to "under 10 percent" (type 2) to "none" (type 1). ^[1]

Type 1. There is a complete absence of UGT1A1 activity. Total bilirubin is typically 342 micromol/L or higher from the first days of life, and the fraction is almost entirely unconjugated. The level is neurotoxic: without rapid treatment the infant develops acute bilirubin encephalopathy, with hypotonia, a high-pitched cry, poor sucking, and, if it progresses, rigidity, opisthotonus, fever, seizures and apnoea. Survivors may develop chronic bilirubin encephalopathy (kernicterus) with movement disorder, sensorineural hearing loss, eye movement abnormalities and enamel hypoplasia. ^[1]

Treatment is aggressive and prompt: phototherapy and, where needed, plasma exchange in the first week of life, to drop the bilirubin before it reaches brain tissue. There is no response to phenobarbital, because there is no enzyme to induce. The definitive (and only curative) treatment is liver transplantation. ^[1]

Type 2. Enzyme activity is under 10 percent of normal, with total bilirubin between 102.6 and 342.0 micromol/L. Jaundice is usually noticed in the neonatal period or later childhood, and most patients do well. Crucially, the residual enzyme can be induced: phenobarbital lowers the serum total bilirubin by 25 to 30 percent. ^[1] The childhood threshold at which to treat is a total bilirubin above 200 micromol/L; above that, phototherapy or phenobarbital should be considered. ^[1] In adults, routine treatment is usually unnecessary, but phenobarbital can be used during a bilirubin surge triggered by illness or stress, or when jaundice impairs quality of life. ^[1]

Imaging and biopsy. Routine liver biopsy is not recommended for Gilbert or Crigler-Najjar. When performed for diagnostic uncertainty, Gilbert shows normal morphology with fine lipofuscin in centrilobular hepatocytes and hypertrophied smooth endoplasmic reticulum; Crigler-Najjar tissue is essentially normal. Brain magnetic resonance imaging in acute encephalopathy shows symmetrical high T1 signal in the globus pallidus, thalamus and basal ganglia; in chronic kernicterus these areas are bright on T2. ^[1]

A useful bedside test. Because type 2 retains some inducible activity and type 1 retains none, a trial of phenobarbital (which lowers bilirubin 25 to 30 percent in type 2 and does nothing in type 1) has long been used to tell them apart, alongside genotype testing. ^[1]

Both are autosomal recessive conditions that produce chronic, predominantly conjugated hyperbilirubinaemia in people who are otherwise well, with normal aminotransferases, alkaline phosphatase and gamma-glutamyltransferase. The defect is not in conjugation but in transport after conjugation. ^[1][2]

Dubin-Johnson syndrome is caused by mutations in ABCC2, which encodes MRP2, the canalicular transporter that pumps conjugated bilirubin and other organic anions into bile. The excretion step fails, conjugated bilirubin backs up into blood and urine, and a characteristic black, melanin-like pigment accumulates in centrilobular hepatocytes, giving the classic "black liver". The gallbladder is normal. Urinary coproporphyrin shows a markedly increased coproporphyrin I fraction. ^[2]

Rotor syndrome is caused by combined deficiency of OATP1B1 and OATP1B3 (SLCO1B1 and SLCO1B3), the sinusoidal transporters that re-uptake conjugated bilirubin from the hepatic sinusoids. The defect is in hepatic storage and re-uptake rather than canalicular excretion, and the liver itself is histologically normal, without pigment. Urinary coproporphyrin is also predominantly type I, but the rise is more moderate (a moderate coproporphyrin I predominance) and the total 24-hour coproporphyrin excretion is usually higher than in Dubin-Johnson. ^[2]

Comparison of the inherited syndromes

Both Dubin-Johnson and Rotor are benign and need no specific therapy; the real danger is misdiagnosis. A persistent direct hyperbilirubinaemia in a person with normal aminotransferases is often worked up as viral hepatitis, Wilson disease or primary biliary cholangitis unless someone thinks of the two syndromes and orders the urine coproporphyrin pattern or the gene panel. ^[1][2]

Imaging is sometimes useful: contrast agents may be handled differently by the two excretion defects, and an oral cholecystogram that normally opacifies a gallbladder may behave differently again. In practice, gene testing has largely replaced those older studies. ^[2]

Haemolysis is the other great unconjugated culprit. Red cell destruction raises the haem input to the liver; a normal liver can conjugate only so fast, so unconjugated bilirubin rises. The inherited syndromes do not destroy red cells, so the laboratory picture is different, and the two must be separated.

• Clinical clues: pallor, jaundice (often mild but fluctuating), dark urine if intravascular, splenomegaly (in extravascular haemolysis such as hereditary spherocytosis), pigmented gallstones in chronic cases.
• Complete blood count: haemoglobin, haematocrit and red cell distribution width. A falling haemoglobin with a stable reticulocyte count initially may be compensated.
• Reticulocyte count: the pivotal test. In Gilbert syndrome it is usually below 1.5 percent; in haemolysis it typically exceeds 3 to 4 percent, or the absolute count exceeds 120 billion cells per litre. ^[1]
• Peripheral blood film: polychromasia, immature red cells and basophilic stippling. Spherocytes, elliptocytes or sickle shapes point to the underlying cause.
• Lactate dehydrogenase: raised from red cell destruction.
• Haptoglobin: reduced, because it binds free haemoglobin for clearance.
• Plasma free haemoglobin: raised in intravascular haemolysis.
• Coombs (direct antiglobulin) test: positive in autoimmune haemolytic anaemia; negative in the inherited syndromes. ^[1]
• Erythrocyte osmotic fragility and sickling tests where ethnicity or family history suggests a hereditary haemoglobinopathy or membrane defect.

Inherited red cell disorders and Gilbert can coexist; a hereditary spherocytosis patient sometimes also carries a UGT1A1 variant, and the bilirubin then climbs higher than either alone. ^[1]

Almost every newborn is a little jaundiced, because red cell lifespan is short in the newborn, gut flora are sparse, hepatic UGT1A1 activity is low, and bilirubin is deconjugated and reabsorbed by the enterohepatic circulation. Most of this is physiological jaundice, usually resolving within 14 days in term infants and within 21 days in preterm infants. ^[1]

Breast milk jaundice is a particular form: components such as pregnane-3,20-diol, certain unsaturated fatty acids and excess lipoprotein lipase in breast milk can inhibit UGT1A1. It appears on days 2 to 3 after birth and settles in 3 to 12 weeks, usually without interrupting breastfeeding. ^[1]

Pathological unconjugated jaundice is caused by increased production (haemolytic disease of the newborn from ABO or Rhesus incompatibility, glucose-6-phosphate dehydrogenase deficiency) or decreased conjugation (hypothyroidism, galactosaemia, Crigler-Najjar). Haemolytic disease of the newborn demands full haemolysis workup with the infant's blood group, direct antiglobulin test, haemoglobin, reticulocytes and smear. Early signs of acute bilirubin encephalopathy in the neonate are hypotonia, lethargy, a high-pitched cry and poor sucking; progression means rigidity, opisthotonus, fever and seizures. ^[1]

Phototherapy thresholds are set locally. Different national bodies (the UK NICE guideline, the American Academy of Pediatrics 2022 revision, Canadian and Japanese guidelines among others) publish hour-specific, gestational-age-specific treatment nomograms for total serum bilirubin, and some differ on when to start phototherapy or to offer an exchange transfusion. The common principle is that CNS type 1 and any jaundice with direct hyperbilirubinaemia bypass those nomograms entirely and need urgent treatment.

Biliary atresia is the emergency to rule out. A newborn with conjugated (direct) hyperbilirubinaemia is not "physiological" and must not be watched. It is cholestasis until proven otherwise. Pale (acholic) stools and dark urine are the clues, and timely surgical referral (Kasai portoenterostomy) within the first weeks of life changes outcomes. ^[1]

Pregnancy. Gilbert syndrome confers no maternal or fetal risk and needs no treatment or change in management. For Crigler-Najjar, pregnancy can be complicated by a surge in bilirubin, so obstetric and hepatology teams plan the delivery and any analgesia that might unmask weakness. Dubin-Johnson and Rotor are likewise benign in pregnancy; oral contraceptives can sometimes unmask a latent Dubin-Johnson jaundice.

Children. Crigler-Najjar type 1 presents in the first days of life and the whole neonatal management is built to prevent kernicterus. Adolescent Gilbert is the commonest "jaundice" a paediatrician sees among students.

Older adults and chronic liver disease. Gilbert can coexist with well-controlled chronic hepatitis B infection, and a persistently raised unconjugated bilirubin in someone whose hepatitis is suppressed is still often just Gilbert. The rule is to exclude haemolysis first, then settle it as coexisting rather than dismissing it.

• Jaundice is often detected late where bilirubin is not measured routinely. Clinical suspicion, inspection of the sclera and skin in bright daylight, and timing from birth remain the first tools.
• Phototherapy can be delivered with cheap, well-maintained light sources, and filtered sunlight protocols have been studied as a bridge in tropical settings with equipment shortages.
• Exchange transfusion requires blood-bank support that many centres do not have; regional referral patterns should be agreed in advance.
• For adults, an isolated unconjugated bilirubin between 17 and about 100 micromol/L in an otherwise well person with a normal blood count almost never needs more than a careful history, a blood count and a reticulocyte count. That is the single highest-value, lowest-cost test.
• Coproporphyrin pattern testing and gene panels are often unavailable; a normal liver biopsy or a characteristic black pigmented liver in Dubin-Johnson is still occasionally diagnostic where gene testing cannot be obtained.
• Breast-milk jaundice and physiological jaundice resolve, but kernicterus is permanent. Any neonate with deep or persistent jaundice, especially beyond day 14 (term) or day 21 (preterm), needs bilirubin measurement and follow-up.

• Bilirubin comes from haem breakdown; the liver conjugates it with glucuronic acid via UGT1A1 and excretes it via MRP2 into bile; gut bacteria turn it into urobilinogen and stercobilin.
• An isolated rise in bilirubin with normal other liver tests is a production, conjugation or transport problem, not hepatitis.
• Unconjugated (indirect) rises: haemolysis, Gilbert syndrome, Crigler-Najjar types 1 and 2, neonatal physiology, drugs.
• Conjugated (direct) rises: Dubin-Johnson (black liver, markedly raised urinary coproporphyrin I) and Rotor (normal liver, moderate coproporphyrin I predominance); both autosomal recessive and benign.
• Gilbert affects 3 to 12 percent of people, gives a bilirubin between 17.1 and 102.6 micromol/L usually under 85.5, is benign, and needs no treatment.
• Crigler-Najjar type 1 has no UGT1A1 activity, bilirubin from birth of 342 micromol/L or higher, no response to phenobarbital, and is treated with phototherapy, plasma exchange and ultimately liver transplantation; type 2 has under 10 percent activity, responds to phenobarbital (25 to 30 percent fall).
• Haemolysis is separated from Gilbert by a reticulocyte percentage over 3 to 4 percent (or over 120 billion per litre), raised lactate dehydrogenase, low haptoglobin and an abnormal smear; the Coombs test is positive only in autoimmune disease.
• Neonatal jaundice is mostly physiological, but kernicterus is permanent and preventable; any newborn with direct hyperbilirubinaemia is an emergency for biliary atresia.
• Treatment thresholds differ by country; the common principle is that CNS type 1 and conjugated jaundice are treated on their own merits, not by nomogram.

Biliary atresia in the newborn; chronic hepatitis B; gallstone disease and bilirubin stones; glucose-6-phosphate dehydrogenase deficiency; hereditary spherocytosis and other membrane defects; haemolytic anaemias generally; neonatal jaundice and phototherapy; Wilson disease and other inherited cholestatic disorders.