Fasting or Not: The Truth Behind Blood Test Requirements

2023-07-03 17:00:00

“To be fasting” is conventionally recommended by doctors before a blood test. However, in some cases, it would not be necessary.

“Being fasting” is a condition frequently requested before taking a blood test. This is not having eaten or drunk anything for at least 12 hours before the sample is taken. It is also recommended not to smoke during this period. However, it is possible to drink water to avoid dehydration, or take medication, unless a doctor indicates otherwise. A study published in 2012 in the magazine JAMA Internal Medicine, had revived the debate on the need to be fasting or not before a blood test.

The role of fasting in blood tests

It is conventionally accepted to fast before a blood test to ensure reliable laboratory results. The explanation lies in the fact that the consumption of sugary foods or drinks can alter the results of certain analyses. For example, imagine you were eating a slice of jam before your blood test. Your glycemia (blood sugar level), your lipids (fat, cholesterol and triglyceride levels) and your iron balance (iron, ferritin) can be affected and mislead the analyses.

Some analyzes therefore absolutely require fasting. According to a published article on the website of Ouilab (llaboratories of medical biology), fasting is imperative in the case of phospho-calcic balance, blood sugar, insulin, lipid balance, bile acids, gastrin, folate (vitamin B9) and CLA allergens -30.

Also, some scans are best done in the morning, such as testosterone, prolactin, crosslaps, aldosterone, renin, cortisol, adrenocorticotropic hormone (ACTH), thyroid status, adrenaline, noradrenaline, l follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol and iron.