Some tests require fasting. This is because after digestion, the blood absorbs nutrients from food, potentially affecting certain test results, explained Dr Ajay Shah, Managing Director, Neuberg Ajay Shah Laboratory, Mumbai.
For instance, if you consume a meal rich in carbohydrates, your body breaks it down into glucose, leading to a temporary spike in blood sugar levels and giving you inaccurate blood sugar test results.
Speaking with the OnlyMyHealth team, Dr Shah suggested that altered results could lead to incorrect diagnoses, treating a non-existent problem while neglecting the actual issue. This is why fasting helps ensure that the measurements remain unaffected by food intake and enhances the accuracy of medical assessments. Let’s take a look at some of the tests that require you to have an empty stomach.
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Blood Sugar Test
A fasting blood sugar test can help diagnose diabetes and also monitor blood sugar levels. It gives the most accurate measurements as Ideally, fasting blood sugar levels should be below 100 milligrams per deciliter (mg/dL), whereas a level of 126 mg/dL or higher is considered indicative of diabetes. A range between 100 and 125 mg/dL may suggest prediabetes, according to the US Centers for Disease Control and Prevention (CDC).
To assess diabetes and monitor blood sugar levels, Dr Shah recommended fasting for at least 8–10 hours to avoid misleadingly high results.
Lipid Profile Test
This test measures total cholesterol, High Density Lipoprotein (HDL), Low-Density Lipoprotein (LDL), and triglyceride levels, which help predict your risk of heart disease and stroke.
Normal total cholesterol levels are typically below 200 mg/dL, whereas high cholesterol levels are said to exceed 240 mg/dL.
To achieve accurate results, it is advised to fast for 9–12 hours and abstain from alcohol for 24 hours.
Liver Function Tests (LFTs)
If you're going for a LFT or liver function test, ensure to fast for 10–12 hours before the test. This is because recent food intake can influence liver enzyme levels in the body, which are proteins that are crucial for metabolic processes such as bile production, nutrient breakdown, and detoxification. Some of the common enzymes measured in an LFT include alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and gamma-glutamyl transferase (GGT), which help assess liver health and diagnose conditions such as hepatitis, cirrhosis, or fatty liver disease.
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Colonoscopy And Endoscopy
Both colonoscopy and endoscopy are test procedures that require fasting.
While colonoscopy involves the examination of the colon and rectum using a flexible tube with a camera at its end, endoscopy uses the same type of tube to look inside the gastrointestinal tract, oesophagus, stomach, and the upper part of the small intestine.
Since these procedures require the doctor to look within the body, fasting is necessary to provide a clear view of the colon or gastrointestinal tract.
The duration of fasting before a colonoscopy and endoscopy can range from 6 to 24 hours, as advised by healthcare providers.
A Final Word
Apart from the above-mentioned tests, many other tests, such as homocysteine, the c-peptide test, and folate deficiency, require 19–12 hours of fasting, said Dr Shah.
While water intake is allowed, consulting your doctor about regular medication before these tests is essential, he added.
In general, it is important to speak with your healthcare provider to prepare for any type of medical test or procedure. This will only help you get accurate results and diagnoses.