Bilirubin is a yellowish pigment produced when hemoglobin in your red blood cells breaks down. Once it breaks down, it’s sent through your liver, gallbladder, and bile ducts before being excreted.

Your doctor may order a bilirubin test as part of a typical comprehensive metabolic panel or liver panel. A liver panel may include liver function tests and total protein tests. Your doctor might also order a bilirubin test if you have certain symptoms.

Usually, bilirubin levels hover somewhere between 0.3 to 1.2 milligrams per deciliter (mg/dL). Read on to learn more about bilirubin and what levels below this range could mean.

If you’re looking at your test results, you’ll probably notice a few kinds of bilirubin, including:

  • Unconjugated (indirect) bilirubin. This type is created when hemoglobin from red blood cells is broken down, bound to a protein in the blood called albumin, and transported to the liver.
  • Conjugated (direct) bilirubin. This type is created when bilirubin attaches to (conjugates with) glucuronic acid in the liver before being excreted. This type of bilirubin is what makes your urine yellow.
  • Total bilirubin. This refers to all of the bilirubin in your bloodstream.

Your doctor might say you have low bilirubin levels if any of these are outside of the usual range.

Low bilirubin levels usually don’t cause any symptoms. Most people don’t even know they have low bilirubin levels until their doctor orders a blood test.

If you have low bilirubin levels and notice any unusual symptoms, make an appointment with your doctor. You may have an unrelated condition that needs treatment.

There aren’t any health conditions that cause low bilirubin levels. But consuming certain substances can temporarily lower them.

These include:

  • caffeine
  • nonsteroidal anti-inflammatory drugs (NSAIDs) called salicylates, such as aspirin
  • barbiturates

Consuming any of these a few hours before a blood test can make your bilirubin levels appear low in your test results.

To avoid this, don’t take any of these substances for at least eight hours before a blood test. Your doctor might also give you additional instructions on other things to avoid before the test for accurate results.

There’s no clear link between low bilirubin levels and any medical conditions. However, some research suggests that bilirubin acts as an antioxidant. Antioxidants protect tissues throughout your body from damage by substances that can cause cells to break down.

Based on bilirubin’s potential antioxidant properties, some believe that not having enough of it can leave certain body parts vulnerable to damage.

This damage could potentially lead to a range of conditions, such as:

Coronary artery disease

Coronary artery disease involves damage to the coronary arteries, which bring fresh blood and oxygen to the heart.

A 2016 study explored the theory that higher bilirubin may offer some protection against coronary artery disease, but couldn’t confirm it. It also didn’t find that low bilirubin levels caused an increased risk of coronary artery disease.

Ulcerative colitis

Ulcerative colitis causes chronic inflammation that can damage your digestive tract.

A 2017 study suggests that lower bilirubin levels might make it harder for the body to remove reactive oxygen species. These are linked to inflammation associated with ulcerative colitis.

Having a low bilirubin level hasn’t been shown to increase the risk of developing ulcerative colitis, though.

Brain lesions

A 2018 study suggests that low bilirubin levels could increase your risk of developing deep white matter lesions in your brain, even if you don’t have any other health issues. These lesions are linked to several conditions, including dementia and heart disease.

Strokes

Low bilirubin levels may also be associated with blood vessel damage, according to a 2009 study.

This type of damage can increase your risk of having a stroke. The study notes that women are less likely to have a stroke related to low bilirubin levels.

Eye disease

A 2017 study found that low bilirubin levels may be a marker for diabetic retinopathy. This is an eye condition that happens when blood vessels near the retina at the back of the eye are damaged.

Keep in mind that much more research is needed before experts can draw any concrete links between bilirubin levels and someone’s risk of developing these conditions.

While high bilirubin levels can indicate several health issues, low bilirubin levels usually aren’t anything to worry about. In some cases, it could be a side effect of a medication you take or having too much coffee before your blood test.

While low bilirubin levels may be associated with certain conditions, this link still isn’t totally clear.

If your test results show you have low bilirubin levels, your doctor will likely just keep an eye out for any other symptoms you have and run another test after some time has passed.