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The Importance of Fasting Before Blood Work in Horses and its Impact on Bilirubin Testing

Updated: Oct 22, 2023

Routine blood work is an essential part of maintaining the health and well-being of horses. Among the various tests conducted, measuring bilirubin levels is crucial for assessing liver function. However, to obtain accurate results, it's imperative that horses fast before undergoing blood work. In this blog, we will delve into the significance of fasting before blood work in horses and how it influences the bilirubin test.

Why Fasting Matters

Fasting before blood work in horses serves several important purposes, all of which directly affect the accuracy of the bilirubin test:

  1. Accurate Baseline Levels: Fasting ensures that the horse's digestive system is in a state of rest. This allows for the measurement of baseline blood parameters without interference from recently ingested food or nutrients. Accurate baseline levels are vital for diagnosing and monitoring various health conditions.

  2. Minimizing Interference: Bilirubin is a pigment produced when red blood cells break down. Its levels can be influenced by the digestion of food, as this process can release substances that temporarily elevate bilirubin. Fasting prevents these transient increases in bilirubin levels, resulting in more accurate test results.

  3. Consistency: Fasting allows for consistent test conditions. Inconsistent results can lead to confusion and potentially unnecessary follow-up tests or treatments, which can be stressful for both the horse and the owner.

Understanding the Bilirubin Test

The bilirubin test is a vital component of equine blood work, as it helps assess liver function. Bilirubin is a waste product formed from the breakdown of hemoglobin in red blood cells. The liver plays a critical role in processing bilirubin, and any dysfunction can lead to elevated bilirubin levels, a condition known as hyperbilirubinemia. High bilirubin levels can be an indication of various liver diseases, including hepatitis, cirrhosis, or cholestasis.

The Fasting Period

Horses should typically fast for 12-16 hours before blood work. This fasting period ensures that the digestive system is relatively empty, minimizing the risk of food interfering with test results. Water should remain available to prevent dehydration. Consult with your veterinarian regarding the specifics of fasting, as individual circumstances may vary. Some horses, such as those with certain medical conditions or young foals, may require different fasting guidelines.


Fasting before blood work in horses is a crucial step in obtaining accurate and reliable results, especially when assessing bilirubin levels to gauge liver function. Proper fasting minimizes interference from recent food ingestion, ensuring that baseline blood parameters, including bilirubin, reflect the horse's true health status. Failing to fast appropriately can lead to inaccurate test results, potentially resulting in unnecessary stress, costs, and confusion for both horse owners and veterinarians. Therefore, it is essential to follow the recommended fasting guidelines and consult with a veterinarian to ensure that your horse's blood work yields the most accurate and valuable information for maintaining its health and well-being.

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