When the best time to take a blood test?

Time in medical analysis is a very important factor, it is best to ask what is the role of time in the accuracy of the test? or what is the use of time in the medical laboratory?
Actually there are two main reasons:
1 – The best time to take the test: Lab doctor asks the patient about special time to take the blood sample
2- The real time to receive the test results: The Patient asks the lab personnel for the waiting time to receive his/her results.
Forget the anxiety of waiting for test results and start understands the meaning of time in the testing.
First discussion will be around the right time to take a sample for testing, begins when official of the lab asks the patient for certain times before to carry out the appropriate test, examples of these:
Fasting time before a test
The last time before or after meal is utilized in the calculation of the fasting period needed to measure a chemical in the blood.
Fasting tests: require the patient to come fasting a certain time before the withdrawal of a blood sample for analysis in the lab, such as:
Analysis of fat in the blood : needs to fasting at least 12 hours .
Why do we need 12-hour fast from food before the analysis of blood fats/lipids?
In healthy people : After about 12 hours the percentage of fat in human serum to the highest rate in the blood , and therefore any increase over the normal rate after 12 hours due to be satisfactory and not because of the food , because the patient had previously refrained from eating half a day.
But; what is the benefit of fasting before a medical analysis?
Determination the time of fasting before going to the lab depends on the type of testing analyte.
For example, the analysis of blood sugar, uric acid, and RBC sedimentation rate need to 6 hours before taking the sample, why?
Because blood sugar up to its lowest level in the blood after 6 hours from the last time of eating.
Uric acid is up to normal level in the blood after about 4-6 hours.
Sedimentation rate of red blood cells: the percentage of sedimentation of blood cells increasing falsely by the existence of excessive food content in the blood fluid.
Thus: The Patient asked to fast before taking laboratory tests because analyte reach its lowest or highest points at that time specified.
However, these tests do not require fasting:
Renal Function test are such as creatinine and urea.
Kidney function enzymes and proteins are such as AST and ALT.
Pancreatic function: Lipase and amylase.
All screening test of viruses and bacteria, such as: HCV ab, HBs Ag, HIV Ab, and Syphilis.
The culture and sensitivity test.
Pregnancy test does not require fasting to be taken.
The time of the last dose of monthly patient treatment 
In the analysis of blood thinners and prothrombin time test the dose of anti-coagulators or anti-thinners medication is depend on results of prothrombin time analysis, and asses in determine a new sets up dose time when the failure of the current dose in maintain blood clotting time. read more about PT time.
In the analysis of blood sugar: the existence of treatment chemical in the patient’s blood before the time of the analysis of blood sugar may decrease the blood glucose level falsely.
In follow-up tests of anemia: the time of the follow-up analysis determines the treatment dose.
Next Menstrual time
The last time deadline for the monthly cycle for the analysis of pregnancy in women
Why the Lab Doctor asks about the next menstrual cycle date before taking a pregnancy test?
It is utilized to distinguish between real and pregnancy or false pregnancy, from promised monthly menstrual period in women.
The best time of pregnancy test to be carried is in the 14 days prior to descent of the blood of next cycle date.
The best time to detect pregnancy in blood after 6 days of pregnancy occurs.
The best time to detect pregnancy in urine and other fluids blood after 10 days post-pregnancy occurrence, because the concentration of the HCG hormone will be in its highest peak.
How long is urine good for pregnancy test?

Urine and stool have to wait up to one hour before bacteria multiplying and begin to convert all chemicals soluble to another forms, the earlier is the best.
For more information about the interpretation of pregnancy test results and the menstrual cycle in women read this topic> here.
Circadian and diurnal test

Tests require to be monitored in a special time during the day:
Cortisol and ACTH monitoring are usually taken two times over the day, AM and PM, because the level of Cortisol/ACTH differs due to biological circadian.
Microbiological tests time
Best time to take Semen analysis: Wait 3 – 6 days after last sexual intercourse without any masturbation to allow testis to produce healthy sperms.
First morning sample of urine and stool is the best time to detect protein in urine and to detect larva and ova of worms in stool, more about stool> here.
Culture and sensitivity test need to stop medication of antibiotics 1 – 2 days before taking the test sample.
Other microbial tests does not require a special time before them.
What does it take for drugs and alcohol to appear in urine or blood sample?
Abuse drugs are such as marijuana “THC”, Canabenoids, cocaine, or opiates.
Alcohols are such as vodka, stilla… etc
The benefits behind choose a time before alcohol and drugs testing the best answer on the usual question:
How long can marijuana/drugs be detected by blood test to receive a new job or military service?
Any chemical found in the blood still upon the person’s metabolism but has what is called “half life time”: it is the time needed to the chemical to be cleared completely even the traces from the blood fluid.
Alcohol and drugs have certain time to be cleared from the blood, the time where NO Alcohol and NO drugs still exist in the blood, depends on how chronic the addicted or smoker is?, usually 1 week for drugs occasional taking and up to 1 month (30 days) for Hooked and Addicted to alcohols.
It’s probably still in your system, although some tricks are used such as drinking water, vinegar and exercising a detox kit/pills if you’re really pressed for time can help get you clean.
Go to a drug store and buy a test kit for like $15. You can check yourself if you will pass, before going to your real pre-work examination. Then you should stop for good.
But, How long you will stay after the sample is taken to receive your results, the next article have more details for this important subject… follow me to be the first to know.

Dr.Megan Ralf

A Medical laboratory Scientist who devoted his life to medical and laboratory sciences, writes his everyday expertise dealing with various pathological conditions through laboratory diagnosis of different body fluids, also participating in many workshops for first aids, infection control, and urgent care. Also Dr Megan Ralf coaching many medical teams.

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