Fasting blood test is a lab test requires a fasting period from eating, drinking, and some medications to get accurate results, here is a list of most fasting and non-fasting blood tests, other non-blood tests have other guidelines.
Why fasting before blood test? Fasting for a blood test means you’re abstaining from eating, drinking, smoking, taking pills for a certain period of time depending on each test rules, fasting is to avoid interference (in general) of some substances in our food and drinks with the substance being tested, and enhance the test accuracy.
How to Prepare yourself prior taking a blood test?
3 things you should know before going to lab:
- Which is the best time to take a blood test?
- Does test require fasting before blood test sampling or other procedures?
- Waiting time for test results.
Can I eat and drink before having a blood test?
If no fasting, the test results can be wrong?
Yes, fasting for some tests is crucial to get correct results which represent your actual condition, however
Can I drink coffee or tea when fasting for blood test?
No, for glucose test any drinks contain sugar will affect the final results.
What should be fasting for?
To abstain from eating and drinking only, or to refrain from certain types of food only, to abstain from alcohol only, refrain from certain types of medications only, or general fasting from everything, other people questions like this:
6 to 12 hours is usually requested, however each blood test has a special fasting times and certain fasting rules, the following fasting tests chart highlights some fasting rules and the proper fasting time before blood test sampling.
I can’t fast too long before a blood test, what should I do?
Some individuals can’t fasting before blood test sampling like the Patients on a critical conditions as those with sever DM, anemia, starving person, newborn, children, pregnant female, and admitted ICU patients after surgery.
Those people have a licence to not fast, and their doctor must know that for proper interpretation.
Most frequent fasting blood test lists:
If your doctor asks for a blood test out of this list, please take the lab advice and your doctor recommendations about medications.
- Fasting blood glucose test requires 8 to 10 hours fasting period before taking the blood sample, only water is allowed, no eating, snacks, caffeine, fruits, or juices.
Glucose tolerance test (GTT) test requires 6 hours fasting from foods and drinks before the first sample.
Glycated hemoglobin test (HbA1C) does not need fasting because A1C levels independent on glucose levels which affected by meals or antisugar pills.
Why fasting before a sugar test? Because blood glucose level is rapidly increase 30 minutes after meals and rapidly reduced after taking glucose-reducing medications.
- The Comprehensive Metabolic Panel (CMP) tests require 10 to 12 hours fasting from foods, drinking, alcohols, smoking, snacks, except drinking water which is not affecting CMP results, CMP blood tests include the following tests:
- Sodium (Na)
- Potassium (K)
- Chloride (C)
- Carbon Dioxide (CO2)
- Albumin (Alb)
- Alkaline Phosphatase (ALP)
- Bilirubin (Bil) Total
- Aspartate Transaminase (AST)
- Alanine Transaminase (ALT)
- Blood Urea Nitrogen (BUN)
- Total Protein
- Calcium (Ca)
- Creatinine (Cr)
However, some tests from CMP doesn’t require fasting if its requested alone, see non-fasting blood tests list below.
- Blood cholesterol test requires 9 to 12 hours fasting before taking a blood sample in the lab or overnight fasting, only water is allowed, no eat, no juice drinks, no snacks, no fruits.
- Triglyceride blood test requires overnight fasting or 12 hours fasting period before the sampling time with no alcohols, smoking, or eating during this period, only water is allowed during this period, drinking alcohols is prohibited, it means no alcohols is allowed before triglyceride blood testing.
- All Lipid profile tests need a 9 – 12 hours fasting, include:
• “good” (HDL) cholesterol
• “bad” (LDL) cholesterol
• total cholesterol
• triglycerides (other fatty substances)
Why blood lipid tests require fasting and no alcohols? blood fats as Triglycerides taking a very long time to be absorbed and metabolized, also it can be converted into glucose or vice versa, so that eating prior to testing blood for fats can show erroneous levels, also alcohols and smoking interfere with those fatty substances in your blood.
However, children, pregnant, diabetic, sever anemic people can abstain for short periods for fasting a blood test due to their critical condition and the doctor should concern these conditions when interpret final results.
Do You know: what does high cholesterol level mean?
- Iron blood test requires overnight fasting, no iron supplements 24 hours before taking iron test.
Why fasting before Iron blood test? Because iron is avidly absorbing iron after meals or taking supplements and lead to temporarily elevated iron level when your blood is being analyzed.
- Gamma-glutamyl transferase (GGT) test requires 24 hours fasting from drinking alcohols and smoking, however addicts need long periods.
Why fasting from alcohols is must for GGT test?
As alcohols and smoking cause damage to your liver integrity and release GGT enzyme from liver cells into the blood stream, Alcohols are the primarily responsible for the high level of the GGT enzyme in the blood, GGT is an alcohol fasting blood test.
- Uric acid test does require 4 to 6 hours fasting, although it’s not must.
- ESR blood test requires a 6 hours fasting period, as the ESR level affected by some foods, ESR results explained.
- Liver function tests require fasting time for 6 hours, LFT panel include:
Transaminases (AST and ALT)
INR and prothrombin test.
Gamma glutamyl transpeptidase
Non fasting blood test lists:
Non-fasting blood tests are those tests which their readings don’t obviously affected by foods or drinks, it means they’re tested randomly at any time during the whole day.
- A1C test is not requiring a fasting period prior to sampling because it depends on glucose particles attached to RBC’s surface and not depends on the circulating glucose.
- CBC blood test is not requiring a fasting period prior testing because it is only counts the blood cells, blood cells count not affected by food type in general.
- Thyroid function tests does not need fasting period, because thyroid hormone is responsible for metabolism processes, hence T4 and T3 is not a fasting blood test.
- TSH blood test isn’t a fasting blood test.
- PSA blood test fasting is not needed, you don’t have to fast from foods and drinking before taking prostate specific antigen test, as no study yet to told us about influence of PSA levels by some foods, however high PSA medications are responsible for lowering PSA levels, so that consult your urologist when testing PSA with taking its medications.
- Blood group type and RH tests does not require fasting before identify the ones blood type.
- Cancer antigens blood tests are not fasting tests in general, when testing for Cancer antigen CA.19.9, it is preferred to fast
- ASO titre, CRP test, Rheumatoid factor test aren’t fasting blood tests.
- Kidney Function tests don’t require fasting before blood test sampling.
- CMP non fasting tests include:
Alkaline Phosphatase (ALP)
Bilirubin (Bil) Total
Aspartate Transaminase (AST)
Alanine Transaminase (ALT)
Blood Urea Nitrogen (BUN)
This Post is to understand which one is a fasting blood test before going to the laboratory, read carefully, and if you don’t find your test here, please drop it in a comment, we promise a good fast help.