Most people treat blood work like a checklist. The doctor orders it, you get poked, and then you wait. But here's the part no one tells you.
What you do before the blood draw can completely change those results. One single mistake, like not fasting properly, skipping a meal, or working out before you get your blood drawn, can lead to the wrong diagnosis or a treatment plan that was never intended for your body. By the way, I'm Dr Mitch Rice, board certified family medicine physician, and today I'm going to walk you through the 10 most common mistakes that I see patients make before they get their blood drawn and what to do instead to make sure that your blood work results are accurate.
Now, the first one is probably the most common mistakes that I see patients make literally all the time, and that's not fasting properly. Many people say they've fasted before the blood work or have not had anything to eat or drink for about 8 hours, but in reality, they drink coffee right before they go get their blood work, or they even have a mint, gum, tea, or even lemon water. And while none of those things individually may seem that bad, here's the truth.
Anything with flavor, even without calories, can stimulate insulin and adrenaline. These drink enhancers can skew fasting glucose results, insulin, and even triglyceride levels. And all three of these are critical for understanding your metabolic health.
The solution to this is to only drink plain water during the fasting window, which is usually about 6 to 8 hours before you get your blood drawn. Again, I'm going to repeat this point because it's so important. If you are getting blood work and your doctor asks you to fast, do not have anything to eat or drink except plain water 6 to eight hours before you get the blood work done.
The second most common mistake I see is skipping essential medications. If you leave out your thyroid pill, anti-depressants, or your seizure medications, your labs can definitely be skewed. Some medications are meant to be taken every single day, even on the day of your lab work, because they can cause unnecessary spikes or drops in blood work, and they can delay the results or the diagnosis and treatment if the blood work results are altered.
An example of this is missing your daily dose of levothyroxine can falsely lower your TSH value and give the impression that your dose is either off or your thyroids out of whack again. Now, the solution to this is to ask your doctor before you get the blood work. Say, which of these medications should I take the morning of and which of these are good to hold?
And if you're ever unsure, bring the list of your medications to the place that you're getting the blood drawn because nine times out of 10, the phabotamist can pretty much have a general idea of which medications you should take that morning and which ones you shouldn't. The third most common mistake that I see is testing blood work either while you're sick, run down, or just inflamed. You may think that a mild cold, a flare up of your allergies, or even a poor night's sleep shouldn't really affect results much, but the truth is these things can make your body out of whack, especially your immune system.
Any one of these situations can temporarily raise your white blood cell count, feritin levels, cedrate and CRP, which are inflammatory markers, and even your blood sugar and cortisol levels. I myself have seen patients mistakenly worked up for autoimmune diseases when they just had a cold the same day that they got their blood work done. The solution to this is simple.
If you're not feeling like yourself, a bit rund down or a bit under the weather, reschedule your appointment for 5 to 7 days in the future. That way you can get the most accurate results possible. Now, the fourth most common mistake that I see, and this one is quite common as well, and that's taking supplements that directly interfere with your lab results.
A lot of people think, "It's just a vitamin. This can't really hurt me, right? " But the truth is, some of the most common supplements can seriously alter your blood work results.
The biggest culprit of this is biotin, which is commonly taken to improve hair, skin, and nails. It can significantly throw off your thyroid markers like your TSH, free T4, and free T3, as well as cardiac markers like troponin. The crazy thing is it's not just biotin that can skew results.
Other common supplements like ashwagandha or rodeiola can alter cortisol patterns. If you're taking too much vitamin D, it can alter your calcium levels. And if you're taking too much zinc or copper, these can compete with each other and falsely alter your iron profile, which can honestly lead clinicians down the wrong paths for working you up for diseases that you probably don't have.
Now, the solution to this is to stop all of your supplements 2 to 3 days in advance before you get the blood work done. Again, if you're not sure which supplements to stop, definitely have that conversation with your doctor before the blood work. If you're on high doses of biotin, more than 5,000 micrograms per day, you're going to want to stop that biotin supplement at least 72 hours before you get your labs done.
Now, the fifth most common mistake that I see is one that typically flies under the radar and doesn't quite get as much attention as it deserves. And this mistake is not being hydrated enough while getting your blood work done. If you don't drink enough water, it not only makes the blood draw harder, but it can concentrate the blood and skew your electrolyte panel.
It's especially important for things like BUN, creatinin, and hemoglobin. The solution to this is to drink plenty of water the day before you get the blood work done, but also the morning of drink about 16 ounces of water 20 to 30 minutes before you get the blood work drawn. That way, the stick is easier and your results are typically going to be more accurate than they otherwise would be.
Now, the sixth most common mistake that I see, and this is one that I typically laugh at quite often because it is kind of hilarious when you get the results back, and that is not telling your doctor about other prescriptions that you may be getting online or at some sort of wellness clinic. If you're using testosterone, compounded thyroid, peptides, or even injectable weight loss medications like simaglutide, these can significantly change things. But the funny part is that the doctor doesn't know that you're taking these medications and then when they get the results that seem way abnormal, it can cause a little bit of confusion.
And the example that I'm personally thinking of, and this has happened to me more than once, and that is I order blood work for certain individuals and they come back and their hemoglobin or red blood cell count is through the roof. And when I see it, I start to panic a little bit. do they may have some sort of red blood cell cancer, but the truth is they're just taking the exogenous or testosterone from somewhere online and doing so can raise the red blood cell count.
That raise in red blood cell count can be concerning, but a simple conversation leads us to the solution. Now, the main point of all this is to make sure that you disclose this information to your doctor. It can save you and your doctor from having a headache.
So, the solution to this is to disclose all your medications and supplements to your physician even if you don't think that they're highly relevant. The seventh most common mistake that I see and I tend to see this in my more health consscious or active patients and that is exercising the morning of before you get your blood drawn. Exercising may temporarily increase creatinin and creatin kynise which may look like muscle damage or kidney disease, liver enzymes, especially as well as glucose and or cortisol which could mimic diabetes.
The solution to this is to obviously avoid vigorous exercise before you get your blood drawn. Now, light walking in the morning, if that's something that you enjoy doing, will totally be fine, but definitely don't do that HIT workout. Save it for after the blood work's done.
Mistake number eight that I see is patients eating heavy, fattier meals about 12 to 18 hours before getting the blood work done. Even if you fast for that six to eight hour period, eating a meal that's high in fat for dinner the night before can spike cholesterol and your triglyceride levels, which can significantly alter lipid profile readings. This is especially important for individuals who have elevated cardiovascular risk, metabolic syndrome, or PCOS.
The solution to this is the night before eat a meal or dinner that's a little bit more bland. It may be higher in protein, a decent amount of carbs, but try to avoid highfat meals. The ninth most common mistake that I see is getting blood work done too soon after a medication change.
I see this in my patients again who are very proactive about their health, which is a good thing. But if you just start your new thyroid medicine or just start a statin and you want to see how your cholesterol or your thyroid panel changes, you really got to wait about 6 to 8 weeks before you see those results make any bit of difference. If you test too soon, your body may not have time to adjust to the medication.
And this could give a picture that the medication is not doing as much as it's supposed to when in reality it's working quite well. Now, the solution to this is to ask your doctor, "How long should I wait before checking these labs? " Again, for most things, it's about 6 to 8 weeks, maybe a little bit longer, but definitely have that conversation.
And the 10th and final mistake that I see patients make frequently is getting blood work done the day before your next doctor appointment. And so, while I applaud you for actually getting the blood work done, because not everybody does that, if you get it done too soon, then your doctor doesn't have time to look at those results. And if we don't have the actual data, we can't help you the best way that we otherwise could.
The solution to this is to schedule your blood work at least 5 to 7 days before your next doctor appointment. This way, if a certain blood test takes 2 to 3 days to get back, your doctor will have all of those results before you go in and not only has time to review them, but also discuss them with you that day. All right, so just a quick recap.
I'm going to do a rapid fire of the 10 most common mistakes starting with number one, and that is drinking water only. That's really the only way that's truly fasting. Take only essential medications.
Postpone your labs if you're feeling sick or run down. Stop supplements that interfere with these labs, especially biotin. Stay hydrated.
Disclose all online prescriptions or wellness medications. No intense exercise the morning of. Keep dinner light the night before.
Wait 6 to 8 weeks after a med change before getting your blood work. And schedule your labs at least 5 to 7 days before your visit. If you can't remember all 10 of these things, don't worry.
I made a PDF talking about everything that we discussed today. And you can get that PDF completely for free down in the link below. Finally, let the wise hear and increase in learning.
And the one who understands obtain guidance. This is from the book of Proverbs 1:5.
