Blood test results can change in a month. In fact, blood test results can change in a week. A month is a lot of time for a lab test result to change and be different from a previous one.
There are many things that can influence a change in blood test results. Here are some to consider:
The time of day, your diet, and the amount of water you have drank can all affect blood test results. The same blood test can have different results in a given day for these same reasons.
For example, a glucose test will be lower if done on an empty stomach as compared to doing it after eating. Also, a blood urea nitrogen (BUN) test can be higher if you are dehydrated as compared to being well hydrated.
Thyroid stimulating hormone (TSH) can fluctuate during the day as well, with higher levels occurring after fasting.
Changes in hormonal levels affect blood test results, also. During the menstrual cycle, iron and TSH levels can be lower. TSH levels also change during pregnancy and after menopause.
Medications can affect blood test results. That’s why sometimes your doctor may ask you if you are taking any medications before doing a particular test or may ask you upon receiving the results. He/she may get you to stop taking them before a test.
A phlebotomist’s technique during needle insertion and collecting blood can affect blood test results. Potassium (K) can be higher if the sample is hemolyzed. Hemolysis can occur during needle insertion or blood collection.
Different labs use different instruments and equipment to perform testing. This can result in a different reading for many tests. So, it’s possible that if you do a CBC at two different labs, the result will be different.
A change in your health status can also result in a change in blood test results. Contracting the flu can affect your CBC, for example.
What causes difficulty drawing blood?
There are many factors that can make it difficult to find a vein or get blood when performing venipuncture. There are some things a person can do to make blood draw easier for the phlebotomist. Also, there are certain techniques a technician can employ to be more successful at drawing blood.
Here are several causes of difficulty:
Having difficult veins: these veins can make it tough when drawing blood.
- Small/thin veins. It gets more difficult if they are deep, rolling, or the person is obese.
- Deep veins. Can be hard to locate.
- Rolling veins. Must be anchored for a better venipuncture.
- Collapsed veins. Occurs with the elderly. Dehydration can cause it as well.
- Constricted veins. A lot of caffeine and nicotine can cause blood vessels to constrict, making the diameter smaller.
Difficult patients: persons in any of these categories pose difficulty when drawing blood.
- Needle-phobia. Do not ignore the patient that says, “I don’t do well with needles.” The stress associated with a fear of needles can affect veins.
- The elderly. Loss of vascular elasticity (blown veins). Muscular atrophy (veins not supported by muscle tissue). State of mind (confused, agitated, combative)
- Pediatric patients. Young ones normally have small veins, although sometimes you can find a good sized vein. They are usually combative and their parents get emotionally overwhelmed.
- Obesity. It’s difficult to palpate veins. The excessive fat tissue hides the rebound bounce. The fatty deposits cause the tourniquet to roll, cutting into the arm.
- Edematous patients. Palpating veins are difficult to impossible because of the interstitial fluid surrounding veins.
- Critical care patients. Difficult to find and palpate veins.
- Vascular scarring: atherosclerosis, drug addicts, chemotherapy patients. Veins are often easy to find but scarring makes needle insertion difficult, causing veins to roll when inserting the needle.
- Dehydration. A lack of water in the body will make it harder to find and palpate veins.
Phlebotomist’s technique or inexperience. A technician’s or nurse’s technique or lack of experience can result in a failed venipuncture attempt. Having someone with experience do the procedure will reduce the number of failed attempts.
I wrote a previous article in which I shared several techniques to use when dealing with a difficult blood draw. Click here to go read it.
Do blood tests hurt more than shots?
Shots hurt more than blood tests as the needle enters the muscle and the vaccine is pushed into the muscle. Also, the needle goes deeper into the muscle than into a vein.
Shots, generally, hurt more but the pain felt when doing a blood test or taking a vaccine may vary depending on who you ask about their experience. Some people will say shots hurt more, while others will agree blood tests hurt more. It’s going to be dependent on their experience.
However, I think some of the pain they have felt is related to the skill of the phlebotomist or the person doing the injection. A good phlebotomist can prick you and you won’t feel any pain, except a small sting when the needle enters the skin and vein. I have drawn blood from many people and after completing the procedure they told me they didn’t feel anything. I have also heard them telling others the same.
If a person has deep veins, the needle will be inserted deeper in their arm as compared to superficial veins. In those instances, inserting the needle to that depth may cause more pain.
If you compare needle insertion for blood draws versus shots, the shots go deeper into the muscle in general. The vaccine has to be pushed into the muscle which can cause some pain. For blood draws, once the needle is in the vein, filling the collection tube doesn’t hurt and nothing is pushed into the vein.
Moving the arm, though, while the needle is in the vein can cause pain. That’s why people are encouraged to remain still while the needle is in the vein.
It does feel weird having a needle in your vein for a minute or two but that doesn’t mean it’s hurting.
And then, when the needle is being pulled out of the muscle, a burning sensation is generally felt that lingers for some time.
There is also the emotional stress that some people experience when doing a blood draw or having a shot. Pain felt during that time may feel like it’s more intense when in reality it’s not.