Bilirubin is a yellowish pigment that results from the natural breakdown of old red blood cells in the body. This byproduct travels through the bloodstream to the liver, where it undergoes processing before being excreted. Understanding bilirubin levels helps to assess liver function and identify certain health conditions.
What is Bilirubin
Bilirubin originates primarily from the breakdown of heme, a component of hemoglobin. Approximately 70% to 90% of bilirubin is derived from the degradation of hemoglobin, with the remainder coming from other heme-containing proteins in tissues like the liver and muscles. This process begins in the reticuloendothelial system.
Heme is converted into bilirubin through a two-stage enzymatic reaction. This initial form, called unconjugated or indirect bilirubin, is not water-soluble and binds to albumin for transport to the liver.
Once in the liver, unconjugated bilirubin is conjugated to become direct bilirubin. This conjugated form is water-soluble, allowing its excretion into bile and then the intestines, where it is eliminated from the body, largely contributing to the color of feces. Normal total bilirubin levels for adults typically range from 0.3 to 1.0 mg/dL (5.1-17 µmol/L).
What Low Bilirubin Might Indicate
Low bilirubin levels, also known as hypobilirubinemia, are generally less common and usually not a cause for significant concern. Often, low bilirubin does not present with specific symptoms and might only be discovered during routine blood tests. However, some factors can temporarily lower these levels.
Certain medications have been shown to decrease bilirubin levels. These include barbiturates, penicillin, caffeine, and high-dose salicylates, such as aspirin. If you are taking any of these medications, your doctor may consider them when interpreting your test results.
Lifestyle choices can also influence bilirubin levels. Heavy alcohol consumption, while often associated with liver issues that can increase bilirubin, may sometimes lead to lower levels. High vitamin C intake has also been noted to potentially decrease bilirubin. Additionally, strenuous exercise, like marathon running, has been linked to lower bilirubin levels.
While no specific health conditions are directly caused by low bilirubin, some studies suggest it might be associated with certain underlying conditions. Low bilirubin levels have been linked to some autoimmune diseases, including rheumatoid arthritis, lupus, polymyositis, and Sjögren’s syndrome. There is also research suggesting a potential association between lower bilirubin levels and an increased risk of cardiovascular disease, as bilirubin possesses antioxidant and anti-inflammatory properties that may help prevent plaque formation.
Low bilirubin has also been explored as a potential marker for other conditions, such as diabetic retinopathy, an eye condition involving damage to retinal blood vessels, and white matter brain lesions, which are linked to dementia and heart disease. However, more research is needed to establish concrete links and understand the full implications. If your test results show low bilirubin, your healthcare provider will interpret these findings in the context of your overall medical history and other laboratory results. Always consult your doctor for personalized interpretation and guidance, especially if you have symptoms or concerns.