Gilbert's syndrome: why your bilirubin is slightly high, and when it's something else

Gilbert's syndrome is a common, harmless inherited trait in which your liver processes bilirubin more slowly, so your bilirubin sits a little above the range, especially after fasting or illness, while your liver enzymes stay normal.

Bilirubin is the yellow pigment left when red blood cells break down, and your liver processes it for removal in bile. In Gilbert's, a variant in the UGT1A1 gene leaves the processing enzyme working at about 30% of normal. Numia's Fatigue Panel and Weight Loss Monitoring Panel report total bilirubin in µmol/L, the Canadian unit.

Here's the surprising part: most people with it probably never find out. BC's liver guideline puts Gilbert's at about 2–7% of people, yet only 0.18% of patients in UK family-practice records had a diagnosis (Veeravalli et al., 2025). In that study, abnormal liver test results were one of the main themes recorded in the year before diagnosis. Knowing your pattern makes the next mildly high result familiar, not alarming.

What does a Gilbert's pattern look like on a blood test?

Reticulocytes are young red blood cells; a high count suggests hemolysis, or faster red-cell breakdown. Numia's panels report bilirubin alongside ALT, AST and ALP, answering the first question: is bilirubin the only result out of range? A family doctor can order direct bilirubin, a CBC and a reticulocyte count.

What makes bilirubin go up with Gilbert's?

Common triggers are fasting or skipped meals, illness, menstruation and heavy exercise, according to the Canadian Liver Foundation. The Merck Manual describes levels that usually move between 34 and 86 µmol/L once Gilbert's is noticed, and visible yellowing tends to appear above about 51 µmol/L. No treatment is needed, though the NHS advises checking with a doctor or pharmacist before new medicines.

When is a high bilirubin not Gilbert's?

A high bilirubin points elsewhere when other results move with it. BC's guideline notes that hemolysis can less commonly cause the same rise in unprocessed bilirubin, and bilirubin also climbs in hepatitis and bile-duct blockage, where liver enzymes usually rise too. Gilbert's is a clinician's diagnosis, usually made by ruling these out.

Get prompt care for first-time yellowing of the skin or eyes, dark urine, pale stools, upper-right belly pain, fever or unexplained weight loss.

Where does Numia fit?

Numia Health, a physician-ordered, at-home blood testing service in Greater Vancouver, brings the usual separate steps into one place. A licensed Canadian physician approves your requisition online in about 3 minutes, and a BC-licensed clinician comes to your home for a 10-minute morning draw. Plain-English results reach the Numia app in 7 days, where the Numia Companion, an AI that has read them, answers questions. Out-of-range results are physician-reviewed with next steps, and an optional wellness consultation is available. Numia is an HSA-eligible service.

Frequently asked questions

What causes Gilbert's syndrome, and does it cause symptoms?

An inherited UGT1A1 gene variant that slows bilirubin processing. Most people have no symptoms beyond occasional mild yellowing. Fatigue is sometimes reported, but the link is unclear, and other causes of tiredness are worth checking; Numia's Fatigue Panel covers five systems.

Is slightly high unconjugated bilirubin always Gilbert's?

No. Hemolysis, including from some medications, can do the same. Normal liver enzymes, no anemia and a level that comes and goes point toward Gilbert's; a clinician makes the call.

Can fasting before a blood test raise bilirubin?

Yes, in people with Gilbert's. After a long fast, illness or hard exercise, a repeat under ordinary conditions gives a fairer read; Numia's Fatigue Panel asks for an 8–12 hour fast. See fasting before a blood test.