High Bilirubin Blood Test: What Does It Mean, and Could It Be Gilbert's Syndrome?

A high bilirubin blood test means the bilirubin in your sample was above the laboratory's reference range. Bilirubin is a yellow substance made when old red blood cells are broken down, and a healthy liver clears most of it into bile. A raised result can come from faster red-cell breakdown, a harmless inherited processing difference such as Gilbert's syndrome, liver disease or a blocked bile duct, so the type of bilirubin and the other results matter.

This guide is for adults reviewing a bilirubin result that has already been reported. It explains the terms on a report and the usual next questions. It cannot tell you why your own result is high, and newborn jaundice follows different rules that are not covered here.

High bilirubin can cause jaundice, a yellowing of the skin and the whites of the eyes. On brown or black skin, the eyes are usually easier to check. The NHS advises an urgent GP appointment or NHS 111 if your skin or eyes look yellow and you have not already been diagnosed with Gilbert's syndrome.

Get help quickly through local services if yellowing comes with dark urine, pale or clay-coloured stools, itching or abdominal pain. Healthdirect Australia advises calling emergency services if jaundice comes with sudden fever, confusion and strong abdominal pain, or if you are vomiting blood. Jaundice in pregnancy should be reported to a doctor or midwife straight away.

If you have already been diagnosed with Gilbert's syndrome, the NHS advises seeking urgent advice when jaundice is worse than usual or does not clear within a few days.

Many reports show total bilirubin and may also split it into two parts. Unconjugated (indirect) bilirubin has not yet been processed by the liver; it travels in the blood bound to albumin and is usually calculated by subtracting direct from total. Conjugated (direct) bilirubin has been processed by the liver into a water-soluble form that can pass into bile.

Cleveland Clinic explains that a rise mainly in unconjugated bilirubin suggests red blood cells are being broken down faster than the liver can process them, or a problem with that processing step. A rise in conjugated bilirubin points more towards trouble clearing bilirubin through the bile ducts, such as gallstones or inflammation. When both rise, the liver itself may be affected.

Cleveland Clinic gives an average normal total bilirubin of about 0.2 to 1.3 mg/dL for children and adults. Other laboratories use different ranges and units, such as micromoles per litre, so compare your number with the range printed on your own report.

Causes are often grouped by where the problem sits. MedlinePlus, Cleveland Clinic and Healthdirect Australia describe the following groups:

• Before the liver: faster breakdown of red blood cells, as in haemolytic anaemia, sickle cell disease, G6PD deficiency or a transfusion reaction.
• Processing differences: inherited conditions such as Gilbert's syndrome and, much more rarely, Crigler-Najjar syndrome.
• In the liver: viral hepatitis, alcohol- or medicine-related liver injury, cirrhosis and other liver diseases.
• After the liver: blocked bile flow from gallstones, inflammation, narrowed bile ducts or, less often, tumours.
• Short-term influences: MedlinePlus notes that some medicines, certain foods and strenuous exercise can affect results, and that an abnormal result does not always mean a condition that needs treatment.

It can be. Gilbert's syndrome is a common inherited condition in which the liver processes bilirubin more slowly, so unconjugated bilirubin builds up from time to time. MedlinePlus Genetics links it to changes in the UGT1A1 gene and estimates that it affects about 3 to 7 percent of Americans. The NHS notes it is more common in men.

Many people find out only because a routine blood test showed slightly high bilirubin. Others notice mild yellowing that comes and goes. Reported triggers include fasting, dehydration, illness, vigorous exercise, lack of sleep, alcohol and menstruation. The NHS says Gilbert's syndrome does not usually cause itching, dark urine or pale stools; if those occur, another cause is more likely.

The NHS describes Gilbert's syndrome as generally harmless: it does not damage the liver, needs no treatment and does not shorten life. It may slightly raise the risk of gallstones, and some medicines may need closer monitoring, so mention it to a GP or pharmacist before starting a new medicine.

A raised bilirubin should not be labelled Gilbert's syndrome on its own. Diagnosis usually relies on blood tests showing a mainly unconjugated rise with otherwise normal liver tests, and a genetic test is sometimes used. If your ALT or other liver enzymes are also raised, see our guide on raised ALT with a normal liver ultrasound.

Clinicians often look at bilirubin alongside the rest of the liver panel, a full blood count and earlier results. A repeat test, a split into conjugated and unconjugated parts, or tests for red-cell breakdown may be arranged depending on the pattern.

MedlinePlus notes that you may be asked to fast for several hours before the test. If you have Gilbert's syndrome, fasting itself can raise bilirubin, so ask how to prepare and record when you last ate. Do not stop prescribed medicines before a test unless you are told to.

Bring the full report, not just a portal flag. These questions can help you leave with a clear plan:

• Which value was high: total, conjugated (direct) or unconjugated (indirect) bilirubin? What reference range and units did the laboratory use?
• Were my ALT, ALP, albumin and full blood count normal, and how do they change the likely explanation?
• Is this result new, or have earlier tests shown the same pattern?
• Could fasting, illness, exercise, alcohol or any of my medicines have affected this result?
• Does Gilbert's syndrome fit my results, and is anything else needed to confirm it?
• Which symptoms should make me seek care before the next planned test?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a raised bilirubin described their test sequence, such as a repeat panel, a conjugated and unconjugated split or blood count checks, can help you notice questions you had not thought to ask. Another person's results cannot explain yours or tell you what you have. Use what you read to write questions for your own clinician, and see our guide on comparing a similar case with your own.

Keep each bilirubin result with its date, units, reference range and the other liver tests from the same sample. Note any fasting, illness, heavy exercise or new medicines around each test. If no one has explained the result or arranged follow-up, contact the team that ordered it and ask who is responsible.