As a phlebotomist, I have drawn blood from the same person more than once but that was because of a specific test the person was doing.
For most tests, blood will be drawn once, however, there are a few tests that require more than one draw.
There are also several factors that influence the number of times blood is drawn from a particular person. Let’s look at these below:
Annual Doctor’s Checkup
As a healthy person you probably don’t go to the doctor’s office often. In fact, probably only a few times have you gone to a doctor before age 40. However, as you get older visiting the doctor’s office may become more frequent.
A visit once a year may become necessary for a healthy aging adult. Such visits are important to just check up on your general health.
For a person with an health issue more visits a year may be needed. Health issues like diabetes, hypertension, and heart and kidney conditions require you to see the doctor more often.
At each of those visits you can expect blood to be drawn at least once or twice for most tests.
Certain Blood Tests
There are a few blood tests that will require your blood to be drawn more than once. Some of these include hormonal, 2HRPP and OGTT tests.
Insulin and Cortisol tests may be done twice during the day depending on what you doctor is looking for.
A fasting blood test (FBS) will be done prior to a 2HRPP test. Blood will be drawn for the FBS and then some more blood will be drawn 2 hours after for the 2HRPP test.
Depending on what the doctor is looking for or is being tested, blood will be drawn 1, 2, 4 or 6 times for the OGTT test.
Certain Conditions/Medications
There are several health conditions and medications that require a person to do blood tests multiple times a day, week or month.
One of those is diabetes. Person’s with diabetes may have to do multiple tests a week to monitor their sugar levels.
Persons who are on blood thinners also have to do regular blood tests to monitor how well their blood is clotting. If there is a change in medication, blood tests have to be done also to see how the new medication is working.
Pregnancy
For those who are pregnant, you can expect blood to be drawn from you multiple times during your pregnancy. Blood will be drawn the most in your first trimester as you may need to do several tests including CBC, Blood Group & RH, Sickle Screen, HIV, Syphilis, HBsAg etc.
The type and number of tests you do may vary slightly depending on your health status and your doctor’s office. Also, somewhere between 24 to 28 weeks you may do other blood tests.
It may be too that if you ever feel sick during your pregnancy, some more blood tests could be done.
Non-Clinical Tests
There are occasions when a person has to do blood tests that are non clinical. These tests are required for certain jobs, scholarships and insurance.
Also, certain tests are needed for immigration purposes. Some of these may include a complete blood count, HIV, Syphilis, gonorrhea etc.
Blood Donation
For blood donation a person can get their blood drawn every 12 weeks or 3 months. That means 3 or 4 times a year, you can have you blood drawn. It is totally safe to donate blood that way if you choose. Some people do it 2 to 3 times a year for several years.
After donating blood the body has to be given some time to build up and replace the amount that was donated. That takes about 3 months.
After 3 months you can donate again or you can wait longer if you desire.
Hospitalized/Intensive Care Patients
If you stay in a hospital a day or longer, you may have blood drawn from you many times. Here are a few reasons for that:
- The doctors don’t know what’s wrong with you. Several tests will be done to find out what’s up.
- You are trying or have been given a new treatment. Testing needs to be done to check out if the treatment is working or not.
- If you have internal bleeding.
- If you are in intensive care. Testing is needed to monitor how you are doing.
How Many Vials of Blood Can be Drawn in a Day?
1 to 6 vials of blood can be drawn in a day depending on the test that is being done. For a particular OGTT test, 6 vials of blood are drawn just over a two and a half hour period.
The number of vials drawn depend really on the type and number of tests a person is doing.
Below is a table showing some common blood tests and the number of vials needed for each test.
| Blood Test | Number of Vials |
| CBC | 1 vial |
| Group & RH | 1 vial |
| Sickle Screen | 1 vial |
| ESR | 1 vial |
| PT/INR, PTT | 1 vial |
| D-Dimer | 1 vial |
| Thyroid Function | 1 to 2 vials |
| HCG (blood) | 1 vial |
| Insulin | 1 to 2 vials |
| Cortisol | 1 to 2 vials |
| 2HRPP | 1 vial |
| Fasting Blood Sugar (FBS) | 1 vial |
| Basic/Comprehensive Metabolic Panel | 1 to 2 vials |
| General Health Panel | 1 to 2 vials |
| O’Sullivan (OST) | 1 vial |
| OGTT (Oral Glucose Tolerance Test) | 1, 2, 4 or 6 vials (depending on type) |
| Lipid | 1 vial |
| Liver Function | 1 to 2 vials |
| STD Screen | 1 to 2 vials |
| PSA | 1 vial |
| HBsAg Screen | 1 vial |
| H Pylori Ab | 1 vial |
| HCV | 1 vial |
For blood donation, a pint or about 473 ml of blood is collected. Compared to a blood test, that is a lot of blood. For example, take an 8ml tube. 473 ml would be about 50 tubes and it is totally safe to give that amount of blood.
However, that amount is only for blood donation. The amount of blood drawn for a blood test or tests is anywhere from 1 to 6 vials a day. There may be times when more than 6 vials are needed but those times are not the norm.
How Long Does it Take to Replenish Blood Drawn?
The body will replace the blood volume in about 24 hours but the components of the blood including the red blood cells, white blood cells, platelets etc. will take longer.
After donating blood, the body will take anywhere from 8 to 12 weeks to replenish what was drawn. The amount drawn for a blood test is way less than the amount drawn for donation.
Therefore, one can expect 4 or 7 vials of blood to be restored much faster. Give it several days and your blood will be back.
How Many Blood Draws are Too Much?
The number of blood draws are dependent on the type and number of tests that are being done. Also, the number of draws may depend on a person’s health condition and the medication that they may be taking.
For persons who are anemic and for small children, taking several vials of blood may be too much. However, the blood tests that are needed are determined by their doctor or health care provider.
Notwithstanding, nurses and technicians should take into consideration the amount of blood that is being collected so that only the amount needed is drawn.