Low Bilirubin: What It Means and When It Matters
Low bilirubin is usually not a problem on its own and causes no symptoms. Most labs treat about 0.2 to 1.3 mg/dL as normal for adults. Research links lower bilirubin with smoking and with higher rates of heart, metabolic, and lung disease, but these are associations, and no treatment to raise it has been shown to help.
- Published
- April 23, 2026
- Last updated
- November 10, 2026
- Read time
- 7 min read
- Medically reviewed by
-
Rhonda Collins, FNP-C
Low bilirubin is usually not a problem on its own. It causes no symptoms, and Cleveland Clinic and MedlinePlus both describe low levels as generally not a cause for concern [1][2]. On average, total bilirubin between 0.2 and 1.3 mg/dL is considered normal for adults and children, although each lab sets its own range [1]. A result below your lab’s lower limit is flagged “L” or “low”. Where low bilirubin gets more interesting is in research: large population studies link lower levels with smoking and with higher rates of heart, metabolic, and lung disease. Those findings are associations, not proof that low bilirubin causes disease, and they are covered below.
What Low Bilirubin Means
Bilirubin is a waste product made when the body breaks down old red blood cells. The liver processes it and clears it into bile [1]. A low total bilirubin means less of it is circulating than your lab expects.
For most people, a low result means one of three things:
- A normal variation. Bilirubin levels differ from person to person, and a value just under the lab’s lower limit is often a healthy person at the low end of the spread.
- A medication effect. Antibiotics, birth control pills, sleeping pills, and seizure medicines can lower bilirubin [1][2].
- Less red cell breakdown than usual. Because bilirubin comes from expired red blood cells, a low level can mean that part of the process of breaking down and clearing old red cells is not running as expected [1].
Low bilirubin is not a diagnosis. It is most useful as one number read alongside the rest of your blood work, such as your complete blood count and liver enzymes. See the Total Bilirubin biomarker overview for how bilirubin fits into a standard metabolic panel.
Normal Total Bilirubin Levels
| Category | Total Bilirubin (mg/dL) |
|---|---|
| Low | Below 0.2 |
| Normal (adults and children) | 0.2 to 1.3 |
| High | Above 1.3 |
These cutoffs are typical averages from Cleveland Clinic [1]. Your lab report lists its own reference range, and that range is the one your result is judged against.
Symptoms of Low Bilirubin
Low bilirubin itself causes no symptoms. There is no recognized syndrome of “low bilirubin.” If you feel unwell and your bilirubin is low, the cause lies elsewhere in your health or your results, not in the bilirubin number.
What Causes Low Bilirubin
The documented causes of a low bilirubin result are:
- Medications: antibiotics, birth control pills, sleeping pills, and seizure medicines [1][2].
- Reduced red cell turnover: fewer old red cells being broken down means less bilirubin is produced [1].
- Smoking: in a study of 715 middle-aged men, 42% of current smokers had bilirubin in the lowest quarter of the group, compared with 16% of people who had never smoked [8].
- Metabolic dysfunction: a 2021 review in the American Journal of Physiology: Endocrinology and Metabolism reports that low bilirubin is most commonly seen in people with metabolic dysfunction [4].
What Research Links to Low Bilirubin
Low bilirubin is not a treatment target today. It has drawn research interest because bilirubin appears to do more than carry waste out of the body. Every finding below is an association from observational or laboratory research. None shows that low bilirubin causes disease, or that raising it improves health.
Antioxidant role. In a 1987 laboratory study published in Science, bilirubin at micromolar concentrations scavenged peroxyl radicals and, at physiological oxygen levels, suppressed lipid oxidation more than vitamin E (alpha-tocopherol) did [3]. That work established bilirubin as a possible natural antioxidant. It was a test-tube study, not a study of people.
Heart and blood vessel disease. A meta-analysis of 11 studies in men found that lower bilirubin went with more severe atherosclerosis [5]. People with Gilbert syndrome, a common inherited trait that keeps bilirubin mildly high, show the other side of the pattern: in one study, 2% of 50 people with Gilbert syndrome had ischemic heart disease, compared with 12.1% of the general population [6].
Metabolic health. The 2021 review “Bilirubin as a metabolic hormone” describes low bilirubin, called hypobilirubinemia, as a possible new pathology that is most common in people with metabolic dysfunction. It proposes that bilirubin acts as a hormone that switches genes on and off, which may explain the link [4]. The authors present this as a research direction, not established care.
Lung disease and mortality. In a UK cohort of 504,206 adults with normal-range bilirubin and no liver or blood disorder, each 0.1 mg/dL higher bilirubin was associated with about 3% lower all-cause mortality and 6% lower chronic obstructive pulmonary disease (COPD) incidence in men, with similar results in women [7].
Smoking. Smokers tend to have lower bilirubin than people who have never smoked [8]. Smoking is also a strong risk factor for heart and lung disease, so it is one reason low bilirubin and these conditions show up together in studies.
When Low Bilirubin Is Worth a Closer Look
A low bilirubin with otherwise normal blood work needs no specific follow-up. It is worth reviewing when it appears alongside other abnormal results, such as very low hemoglobin, platelets, or white cells, or abnormal liver enzymes. If that is your situation, review the full set of results with your doctor.
Rechecking is simple. A fractionated bilirubin test measures total, direct, and indirect bilirubin. A hepatic function panel adds liver enzymes and proteins for broader liver context. For the opposite result, see high total bilirubin, and for the most common cause of mildly high bilirubin, see Gilbert’s syndrome symptoms and blood tests.
Frequently Asked Questions
Which is worse, high or low bilirubin?
High bilirubin is more likely to need attention. It can signal a liver problem, a blocked bile duct, or fast red cell breakdown, and very high levels cause jaundice [1]. See liver disease symptoms and blood tests for how doctors work that up. Low bilirubin is generally not a cause for concern on its own [1][2]. Not every high result is a warning sign either: Gilbert syndrome, a common inherited cause of mildly high bilirubin, has been linked to lower rates of ischemic heart disease [6].
What autoimmune diseases are linked to low bilirubin?
The clearest link is with systemic lupus erythematosus (SLE). A 2023 meta-analysis of five case-control studies found lower bilirubin in people with lupus than in healthy controls, and lower levels in active lupus than in inactive lupus [9]. This shows bilirubin tends to be lower when lupus is present and active. It does not show that low bilirubin causes lupus, and a low result does not suggest that you have it.
Are there natural treatments for low bilirubin?
No treatment to raise bilirubin has been shown to improve health. The 2021 review describes therapies that target bilirubin as future research, not current care [4]. The lifestyle link with the best evidence is smoking: smokers tend to have lower bilirubin [8], and stopping smoking has well-known benefits for heart and lung health regardless of what it does to bilirubin.
Should I be worried if my bilirubin shows up as “L” on my lab report?
Usually not. An “L” flag near the bottom of the reference range is common, and Cleveland Clinic and MedlinePlus both describe low bilirubin as generally not a cause for concern [1][2]. Check whether you take any of the medications listed above, and read the result alongside the rest of your panel.
References
- Cleveland Clinic: Bilirubin test
- MedlinePlus: Bilirubin blood test
- Stocker R, et al. Bilirubin is an antioxidant of possible physiological importance. Science. 1987
- Creeden JF, et al. Bilirubin as a metabolic hormone: the physiological relevance of low levels. Am J Physiol Endocrinol Metab. 2021
- Novotný L, Vítek L. Inverse relationship between serum bilirubin and atherosclerosis in men: a meta-analysis of published studies. Exp Biol Med. 2003
- Vítek L, et al. Gilbert syndrome and ischemic heart disease: a protective effect of elevated bilirubin levels. Atherosclerosis. 2002
- Horsfall LJ, et al. Serum bilirubin and risk of respiratory disease and death. JAMA. 2011
- Schwertner HA. Association of smoking and low serum bilirubin antioxidant concentrations. Atherosclerosis. 1998
- Yu Y, et al. Relationship between bilirubin and systemic lupus erythematosus: a systematic review and meta-analysis. Immun Inflamm Dis. 2023
Related Resources
- Total Bilirubin: Biomarker Overview
- High Total Bilirubin Symptoms: Causes, Signs & What to Do
- How to Improve Your Total Bilirubin Naturally
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