Fasting blood tests

Several hours of fasting are necessary for some blood tests. But not everyone is aware of which ones and what it means to approach them empty-handed.

Each of us needs to get a general blood test at least once a year. This is the best method for spotting many diseases in their early stages, which increases the likelihood of a cure and speeds up recovery. We are able to submit test applications “on the go” throughout the day. Some blood tests, however, necessitate several hours of fasting in order for the results to be trustworthy. What does this mean, and how should you proceed?

What does fasting mean?

This implies that at least 6 hours and ideally 8 hours must have passed since the last meal. It even says 12 hours in some cases. You are permitted to consume only water during this time (but in limited quantities, unsweetened, and non-carbonated).

Drink pure, boiled, or non-carbonated spring water before the test, as mineralized water can affect blood composition and falsify test results.

In practice, it is better to attend such examinations in the morning; a good night’s sleep ensures a proper break, and the findings are more dependable. If the exam is in the evening or afternoon, have a light, modest meal in the morning and remember to take a six-hour rest.

Before the test, do not smoke, drink coffee, chew gum or take medications that you normally take (unless your doctor tells you otherwise).

How to prepare a child for a fasting blood test?

In the case of children, the matter is more complicated. It is difficult for toddlers to keep a long distance from a meal. Much depends on the age of the child. 

  • Babies do not need to go without food for the test, but they should not be fed just before the blood is drawn. 
  • Children up to 3 years of age  (if necessary) may eat a light meal before the examination. The only exception is a glucose test, before which you must not eat anything, because the result will be disturbed. 
  • Older children are treated as adults in the case of examinations, i.e. they should be on an empty stomach, and they can eat their last meal the evening before. 

What tests should be done on an empty stomach?

  • blood count ,
  • OB,
  • reticulocytes and platelets,
  • bleeding + clotting time,
  • total protein,
  • albumin,
  • bilirubin with fractions,
  • liver tests (AspAt, ALAT transaminases),
  • lipidogram (total cholesterol and its HDL and LDL fractions),
  • triglycerides,
  • urea, creatinine, uric acid,
  • glucose,
  • sugar curve ,
  • iron,
  • calcium, phosphorus, magnesium, sodium, potassium, chlorides,
  • Thyroid hormones,
  • c-peptide,
  • insulin,
  • hbA1C (glycated hemoglobin),
  • ferritin,
  • vitamin B12,
  • Folic acid,
  • sex hormones,
  • aldosterone, cortisol,
  • viral diseases (jaundice, toxoplasmosis , mononucleosis, whooping cough, chicken pox , etc.),
  • monitoring the concentration of certain drugs.


4th Professional Medical Student. Karachi Medical and Dental College.

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