Is it necessary to fast before a complete blood count (CBC) test?

In general circumstances, a routine blood test refers to a complete blood count (CBC). Whether a CBC requires fasting depends on the specific situation. If only a CBC is being performed, fasting is generally not required. However, if the CBC needs to be conducted alongside other tests that require fasting, then fasting may be necessary. The detailed explanation is as follows:

A standalone CBC typically does not require fasting. A CBC mainly involves drawing venous blood to measure components such as red blood cells, white blood cells, platelets, and hemoglobin, which primarily reflect the basic components and quantities in the blood. Since proteins, lipids, carbohydrates, and trace elements in food are mainly converted into small molecules after entering the bloodstream and have minimal impact on blood cells, a standalone CBC does not require fasting.

If the CBC is being performed together with other tests that require fasting, such as liver and kidney function tests, blood glucose, or lipid profile, then fasting is recommended to ensure consistency of test results. After eating, blood glucose and lipid levels can significantly increase, and certain indicators of liver function may also change. Conducting these tests after eating could affect the accuracy of the results. Therefore, if the CBC is combined with these tests, it is advisable to fast.

Regardless of whether the CBC is performed fasting or not, patients should maintain normal作息 (作息 should be replaced with "作息" in Chinese context, but here it should be translated as作息 patterns and dietary habits before the test, and avoid excessive fatigue and emotional fluctuations that may affect the test results.)作息 patterns and dietary habits before the test, and avoid excessive fatigue and emotional fluctuations that may affect the test results.