Should you fast before having a blood test?

We undergo several blood tests in a year. Since the blood reports are the most accurate way to determine the biological well being of a person, we should know a thing or two about the do’s and don’ts of blood tests.

"When you are preparing for any health check-up, your focus is mainly on silent diseases," says Dr Shashikant Nigam, Senior Consultant, Internal Medicine, Apollo Hospitals, Ahmedabad emphasizing on the growing incidences of diabetes, cardiovascular diseases and other chronic illnesses.

Adding more information to this and segregating the nature of the tests, Dr Anubhav Pandey, Head, Clinical Labs, Department of Microbiology, Amrita Hospital, Faridabad says though fasting is essential for many blood tests, it solely depends on what kind of test you will have. "The prerequisite for every test is unique and it entirely depends on the type of blood tests being performed. For example, to test the fasting blood Glucose and liver function, the sample must be given in a fasting state," he says.

In the same line Dr. Dilip Gude, Senior Consultant Physician, Yashoda hospitals Hyderabad says, "A few tests like Fasting blood sugar, Lipid profile, GGT(Gamma glutamyl Transferase),iron profile etc and upper gastro endoscopy need to be done in a fasting state. Although not mandatory some other tests like LFT(Liver function test], serum electrolytes, serum creatinine, vitamin B12 are recommended to be done fasting."

The experts say anywhere between 8-12 hours of fasting is good enough. For Glucose, 10-12 hours of fasting, and 12-14 hours, for Lipid profile (Cholesterol) are required, says Dr Nigam.

Emphasizing more on the importance of the fasting period, Dr Pandey recommends: If there is any fatty meal in the preceding 8-12 hours, it is recommended to get tested on another day.

"When there is intake of food in the preceding 8-12 hours, there are certain biochemical processes which are underway and leads to false interpretation of their levels in blood. Analytes such as Triglycerides and LDL Cholesterol may be elevated after a high-fat meal in the preceding 72 hours of sample collection and might lead to clinical misinterpretation," explains Dr Pandey.

"During endoscopy if the patient is not fasting, there may be food particles that occlude clear view of stomach and esophagus," explains Dr Gude and adds that in such cases aberrant or false readings will be reported.

No, you cannot.

"Food items taken with or without milk will alter the level of glucose and lipids because Serum (supernatant fluid obtained from blood after centrifuge), which is used for estimation, becomes cloudy, and we will end up getting wrong reports. Hence fasting is mandatory," explains Dr Nigam.

On this, Dr Pandey explains about diuresis or excessive urine. He says, "diuresis after consumption of Coffee and tea may lead to dehydration and multiple attempts may be needed to find a suitable vein, making the process of blood collection painful."

Yes, say the experts.

Water does not interfere with the quality of serum for these tests, says Dr Pandey.

"Usually about 6 and half to 7 hours of sleep is recommended. Heightened anxiety,insomnia, having alcohol the previous night, smoking, chewing gum, strenuous exercise before blood tests etc should be avoided as the readings may be falsely elevated or decreased," says Dr Gude.

"Certain tests like cortisol levels might get elevated due to stress and lack of sleep," says Dr Pandey.

Dr Nigam says insufficient sleep can alter the reports of diabetic patients. "Quantity of sleep can sometimes give altered reports in the case of diabetic patients who are on regular treatment," he says and recommends proper sleep before blood test.

No.

It is not necessary at all, as blood reports are not affected by empty bowels but are directly related to an empty stomach.

“Most doctors do not tell diabetics that their sugar can drop and it can be dangerous”