The most common cause of high bilirubin in a teenager is Gilbert’s syndrome, a harmless genetic condition that typically shows up for the first time during puberty. Less often, elevated bilirubin points to red blood cell breakdown, a viral infection affecting the liver, or, rarely, an underlying liver or bile duct problem. Normal total bilirubin for anyone over 15 days old through age 17 is 0.0 to 1.0 mg/dL, and jaundice (the visible yellowing of skin and eyes) usually doesn’t appear until levels reach two to three times the normal range.
Gilbert’s Syndrome: The Most Likely Cause
Gilbert’s syndrome affects roughly 5 to 10 percent of the population and is by far the most frequent reason a teenager’s blood work shows elevated bilirubin. It’s a genetic quirk in how the liver processes bilirubin, not a disease. The liver enzyme responsible for packaging bilirubin for removal works at reduced capacity, so unconjugated (indirect) bilirubin builds up mildly in the bloodstream.
Most cases are diagnosed right around puberty, for a few overlapping reasons. Teenagers have higher hemoglobin turnover than younger children, and the surge in sex hormones during puberty further slows bilirubin processing. Males are affected more often, likely because of higher bilirubin production and the specific hormonal environment of male adolescence. Many teens with Gilbert’s syndrome have no idea they have it until routine blood work flags their bilirubin as elevated.
When symptoms do appear, they’re usually limited to mild yellowing of the whites of the eyes. Several everyday situations can push bilirubin higher temporarily: skipping meals or fasting, dehydration, illness with a fever, physical exertion, stress, and menstruation. These episodes are harmless and resolve on their own once the trigger passes. Gilbert’s syndrome requires no treatment.
Hemolytic Conditions: Red Blood Cell Breakdown
When red blood cells are destroyed faster than the body can replace them, the hemoglobin inside them gets broken down into bilirubin. This produces a rise in unconjugated bilirubin, similar to Gilbert’s syndrome on paper but caused by a completely different mechanism. The key difference is that hemolytic conditions also cause anemia, so a complete blood count will show low red blood cell numbers or abnormal red blood cell shapes.
Several inherited conditions can cause this pattern in teenagers:
- Sickle cell disease causes red blood cells to become rigid and break apart. Teens with sickle cell disease usually already know their diagnosis, but bilirubin can spike during pain crises.
- Thalassemia is the most common inherited hemolytic anemia worldwide. It results from problems manufacturing hemoglobin, leading to fragile red blood cells.
- Hereditary spherocytosis produces abnormally shaped, sphere-like red blood cells that get trapped and destroyed in the spleen.
- G6PD deficiency is an X-linked condition seen almost exclusively in males. Red blood cells lack an enzyme that protects them from oxidative damage, so certain foods (like fava beans), medications, or infections can trigger sudden episodes of hemolysis.
Infections That Affect the Liver
Mononucleosis, caused by Epstein-Barr virus, is one of the most common infections in teenagers and frequently involves the liver. In one large study of nearly 400 patients with mono, about 15 percent had bilirubin levels between 1.5 and 3 mg/dL, and another 12 percent had levels above 3 mg/dL. Visible jaundice shows up in roughly 5 to 6 percent of mono cases. The bilirubin elevation is temporary and resolves as the infection clears, though it can take several weeks.
Hepatitis A, B, and C can also raise bilirubin by directly damaging liver cells. Hepatitis A tends to cause a more acute illness with noticeable jaundice, while hepatitis B and C can be subtler. Any teen with unexplained elevated bilirubin and abnormal liver enzymes will typically be tested for these viruses.
Strenuous Exercise
Teenagers who are serious athletes sometimes show mildly elevated bilirubin after intense training or competition. Hard aerobic exercise, particularly running, can physically damage red blood cells through repeated foot strikes, elevated core temperature, and muscle breakdown. The hemoglobin released from those cells gets converted into bilirubin. Studies have confirmed that plasma bilirubin rises in both trained and untrained adolescents after running to exhaustion, and in football players after maximal exercise testing.
This spike is usually short-lived. Markers of exercise-induced hemolysis tend to appear only immediately after intense effort and drop back to baseline within days. If your teen’s blood was drawn shortly after a hard practice or game, that alone could explain a mildly elevated result. Chronic, high-volume training (around 170 minutes per week of vigorous exercise in one trial) can produce a more sustained, though still modest, increase.
Liver and Bile Duct Problems
Less commonly, elevated bilirubin in a teenager signals a problem with the liver itself or with the bile ducts that carry bilirubin out of the liver. These conditions raise conjugated (direct) bilirubin rather than unconjugated, which is an important distinction on lab results. A direct bilirubin level above 1.0 mg/dL when total bilirubin is also elevated is considered abnormal by pediatric gastroenterology guidelines.
Autoimmune hepatitis occurs when the immune system attacks liver cells. It can start in adolescence and tends to cause fatigue, abdominal discomfort, and progressively worsening liver enzymes. Wilson’s disease is a rare inherited condition in which copper accumulates in the liver and brain. It often presents in the teenage years, and initial testing involves measuring a blood protein called ceruloplasmin (which runs low) and collecting a 24-hour urine sample to check copper levels. Gallstones, while less common in teens than adults, can block bile flow and raise direct bilirubin, particularly in teens with sickle cell disease or other hemolytic conditions that produce excess bilirubin over time.
How Doctors Figure Out the Cause
The diagnostic process starts with distinguishing between the two forms of bilirubin. If the elevation is mostly unconjugated (indirect), the issue is either overproduction of bilirubin from red blood cell breakdown or underprocessing by the liver, as in Gilbert’s syndrome. If conjugated (direct) bilirubin is elevated, the problem lies in the liver or bile ducts.
From there, a standard workup typically includes a complete blood count to check for anemia or abnormal blood cell counts, a reticulocyte count to see if the bone marrow is working overtime to replace lost red blood cells, and liver enzymes (AST and ALT) to detect liver cell damage. If liver enzymes are normal and the teen is otherwise healthy with only mildly elevated unconjugated bilirubin, Gilbert’s syndrome is the most likely explanation, and no further testing may be needed.
If the picture is less clear, doctors may order viral hepatitis panels, tests for autoimmune markers, or specialized studies like ceruloplasmin and urine copper if Wilson’s disease is a concern. The presence of bilirubin in a urine sample is a quick clue that points toward conjugated hyperbilirubinemia and suggests the liver or bile ducts need closer evaluation. In many cases, though, the answer turns out to be Gilbert’s syndrome discovered incidentally on routine labs, requiring nothing more than reassurance.