Comparing Your Own Lab Results Across Different Labs Or To Other Patients: Convert Your Numbers To A Percentage


When you get your lab results back, it can be helpful to convert your numbers into a “percent of normal range” value.  For many of the tests, you will then be able to compare and contrast your results easily over time, and with other patients, no matter what laboratory ran your tests.  If you are on thyroid medication, the same is true with your thyroid dosages.  This will become more clear as you read on.

This section is not about interpreting your test results, which is why I didn’t use the word “Interpretation” in the section heading.  The bottom line is, your doctor should be providing the interpretations of your lab values and differential diagnoses.   This is why they went through years and years of med school, internships and residencies.  Still, we all know how that goes.   Too often a doctor simply looks at the results and sees the same things we do:  either your lab values are “normal” or “abnormal”, depending on the numbers the lab sends back.  The report will state quite clearly what the normal numbers or range of numbers should be, and then will state if the patient’s numbers/results are in that normal range or not.  Sometimes the lab even puts your abnormal value in red, just to be extra helpful and give your doctor an additional hint in case they are hurried and don’t look at your report too closely.   For some doctors, this is as much a scrutiny as your test results will get.  Unfortunately for you, this is acting more like a technician, who just reads the numbers, instead of like a physician, who will try to interpret your numbers in the greater context of your symptoms and other lab values overall, over time.   Ultimately, we all need a good physician who will take the time to actually think about complex cases and what those lab numbers really mean in our individual case.

As patients, too often we’re stuck with the “technician” kind of doctor.  Although we as patients often can’t hope to make the educated interpretations from our reports than an excellent physician can, we CAN easily look at our lab data like a technician.  It’s just not that hard to tell when your own lab values are “in range” or “not in range”, simply because the report tells you that information.  And like I said, sometimes the abnormal values will even be in red colored font for you.    For the most part, I leave the question of what your abnormal value may mean (or, the interpretation), to your doctors or other resources you may go to try and figure things out if you’re stuck with a technician for a doctor.    I do cover a few patterns I feel are significant in Thyroid Hormone Medications.   Here, I’ll cover some simple techniques to be able to make valid comparisons of your lab data (thyroid values) from different labs, or to easily make comparisons of lab data between patients.


Comparing Lab Result Values Across Different Labs:

I cut and pasted this information from another document I wrote.

When you get your lab results back, they may look something like this:

Your result:  fT4 = 1.11              Normal range:  (0.75 – 1.54)

When posting your fT4 result, or talking with someone else about it, whether that’s your doctor or not, it’s always important to provide the “normal range” numbers.   Simply saying “My fT4 level was 1.11” is meaningless.  This is because every laboratory has a different “normal range” for numbers.  These “normal range” numbers can be different based on the types of laboratory equipment they use, or the units of measurements may differ, and even change daily depending on their quality control checks.  This is normal, so you don’t have to be concerned by these changes.  All you need to know is your own lab result AND the normal range for that lab result.  And when posting your results, always post the normal range values with it, like so:  fT4=1.11 (0.75-1.54).   Here, you can easily see that 1.11 is somewhere between 0.75-1.54.  But maybe a friend of yours used another lab, and her lab value came back as fT4=320 (normal range 220-480).  Both of you have fT4 values in the normal ranges, but which of you has a higher fT4 value?

By converting lab results to a “percent of range” value, I could compare lab results no matter what lab they came from.  Different labs will use different assays, as well as run QA/QC checks on instrumentation that will often result in slight variations of the “normal range” for a parameter.  Just as an example, let’s say that the “normal range” for fT4 for Lab A ranges from 5-15.  Intuitively, you know that if your results come back at 10, you are at “50% of range” – 10 is right between 5 and 15, halfway between exactly, which is 50%.

  • The way to calculate this is: (10-5) / (15-5) = 5 / 10 = 0.5 = 50%.  (Note:  this example was in error initially due to a typo; I finally caught it Dec 2015 and corrected it.  My apologies, I know it’s totally unhelpful to have errors in examples like this!).
  • Another example: Lab B has normal ranges of fT4 from 0.75 – 1.54. My result = 1.11. The calculation is: (1.11 – 0.75) / (1.54 – 0.75) = 0.36 / 0.79 = 0.45569 = 45.6%.
  • Another example: Lab C has normal ranges of fT4 from 0.82 – 1.77. Note how these fT4 normal ranges are different than the previous example of Lab B and Lab A. My fT4 result at this lab = 1.25. The calculation is: (1.25 – 0.82) / (1.77 – 0.82) = 0.43 / 0.95 = 0.4526 = 45.3%.
  • Note how even though the numerical values of 1.11 from Lab B and 1.25 from Lab C are different, the “percentage range of normal” is essentially the same (45%).   This is the information we’re interested in – the “percentage of range” allows us to compare lab values across labs. You cannot compare the actual numbers you get from different labs to determine where you are within the normal ranges, because these normal ranges differ for each lab. This is also the reason you cannot simply say my fT4 = 1.11 and leave it at that for someone to evaluate. You need to always include the normal ranges with your result, in order to make a useful evaluation of where you’re at.
  • Back to my first example: with a fT4 of 320 (220-480), the calculation is (320-220) / (480-220) = 100/260 = 0.3846 = 38.5%.   Comparing this to fT4 = 1.11 (0.75 – 1.54), the calculation is: (1.11 – 0.75) / (1.54 – 0.75) = 0.36 / 0.79 = 0.45569 = 45.6%. So the person with a fT4 = 1.11 has slightly higher percentage of fT4 in her blood than the person with a fT4 = 320. By talking “percentages” now you both have a feel for how “normal” or “abnormal” your value is within the unique and differing normal ranges provided by each lab.


When people take Armour or the other naturals, they typically will have a blood result with fT3 being higher than fT4.  The popular recommendation is that “your fT4 should be at about 50% or range, and your fT3 should be at about 80% of range or higher”.  Please note that for starters, this only occurs when you take Armour or another “natural”, because of the higher ratio of T3:T4 in the NDT’s.  So this recommendation does not apply to other thyroid medications, and it’s also not something for “everyone” to strive for.  Again, there is not a “one treatment fits all” when it comes to thyroid problems.  Because of my extreme sensitivity to T3, I could not tolerate having a fT3 blood level this much higher than fT4 blood level.   And when I tried to force the issue, either by taking the NDT’s or the synthetics with a higher T3 ratio, I ended up making my symptoms much worse, not better.  For me, whether I was taking thyroid hormone or not, I felt best when my frees were balanced (ie, more of a 1:1 ratio blood level wise).  I never had a full thyroid panel done before being floxed; I only had a few TSH levels.  So I don’t know if that’s always been my “own personal genetics and physiology”, or something that developed when I was floxed.

One other note:  Thyroid antibody test results are unique and specific to the lab that tested them.  You cannot compare antibody values between labs.  Various labs use various assays with different techniques, and antibody testing is not as standardized or reliable as hormone testing is.  If you’re going to monitor your antibody status over time, you’ll need to use the same laboratory, using the same techniques, in order to reliably compare and see trends.  A good example of this is the TgAb test.  I read a research paper describing 4 different methods of testing for these that labs will use, and describing the different results each lab got using same samples.  I tested myself using labs that used two of these techniques.  I started out with Tg antibodies in both labs, but Lab 1 numbers were much lower than Lab 2 numbers.  Eventually, Lab1 numbers reported my Tg antibodies had declined to undetectable levels – good news!  But Lab 2 antibodies of a sample drawn within a week or two of the first sample was well beyond the “normal range” for that particular lab.  This in no way suggests that Lab1 is “not as good” as Lab2.   Specificity and sensitivity for antibody testing is simply changing over time, and determining testing techniques, as well as normal standard deviation within normal populations, is constantly under flux and re-examination as technology continues to improve.  There was not necessarily a “right” answer here; just a decision for me to make as to how I was going to continue monitoring these particular antibodies within me.

Another example is testing for the TSI antibodies.  Some labs will report these antibodies as below a certain percent, for example, your result might be “less than 140%”.  You won’t know if your number is zero, or 135%; all you know is that your value was less than 140%.  This means you don’t have fully blown clinical Grave’s disease, which is defined as anything above that 140% for that lab.  But unfortunately, it doesn’t let you know if you do in fact have these antibodies, just at a level that’s below 140%.  So I preferred having my TSI’s analyzed at LabCorp, because they provided an actual number, even if it was below their diagnostic level of 139%.  For example, one of my TSI results was:  72% (0-139%).  This result is telling me that I do, in fact have these TSI antibodies – just not at a level that would be considered full blown Grave’s disease.  Some people believe that any antibodies above 1-2% is indicative of “subclinical” Graves; I don’t know how true this is, but I tend to agree with this.  These antibodies will be affecting TSH whether they are at a low level or high level, and I watched these antibodies go up and down in accordance with my symptoms and dosages.  As with my other antibodies, I found these lab measurements to be consistent and predictable over time, which I thought was interesting.

I felt quite comfortable with the consistency and trends I observed over time with my own antibody testing.  Using the same lab over and over again, antibodies went up and down in a very consistent and predictable fashion with me.  I was testing quite frequently (monthly or more), and even the small increases or decreases, which most researchers would dismiss as being insignificant, none the less were 1)consistent, and 2)very predictable.  I grew to trust the usefulness of such testing in myself because of this.


Calculating Thyroid Medication Dosages using Percentages:

As I said earlier, I could not tolerate a high percentage of T3 as my thyroid hormone dosage.  I desperately needed some T3 – without it, I literally felt as though I was dying.  On the other hand, having too high a serum ratio, or dosage ratio, of T3, was something I couldn’t tolerate either.  In general, I did best when taking a dosage combination of about 90-95% T4 and 5-10% T3.  I really couldn’t get any higher than 10% of T3 the first time I was on thyroid hormone, and this sensitivity increased to the point that I could only tolerate about 5% T3 the second time I started TH.

Let’s use a 90%T4/10%T3 dosage combination as an example.  Again, I express this as a percentage, because absolute numbers of thyroid hormone replacement dosages vary among individuals.  Here are some examples of different people on a 90%T4/10%T3 dosages:

  • Person A is on 100 ug/day total thyroid hormone replacement. 90 ug of that is T4, and 10 ug of that is T3. Therefore, person A is on a 90%T4/10%T3 per day replacement dose.
  • Person B is on 70 ug/day total thyroid hormone replacement. 62.5 ug of that is T4, and 7.5 ug of that is T3. Therefore, person B is on 62.5/70 = 89.3% T4, and 7.5/70 = 10.7% T3. This is close to the 90%T4/10%T3 ratio.
  • Person C is on 125 ug/day total thyroid hormone replacement. 112.5 ug of that is T4, and 12.5 ug of that is T3. Therefore, person C is on 112.5/125 = 90% T4 and 12.5/125 = 10% T3.


An important concept to note is that each grain (60 mg tablet) Armour Thyroid medication consists of 38 ug T4 and 9 ug T3 (yes, this total is way less than 60 mg because the fillers make up the rest of the tablet; note also the difference between ug (micrograms) and mg (milligrams)).  This means that the T4 and T3 percentages are 38/47 = 80.9% T4 and 9/47 = 19.2% T3.   It won’t matter how much or how little Armour you take, this ratio always stays the same.  You can’t control the amounts of T4 and T3 individually when you take Armour or the other naturals.  Every time you raise or lower your Armour dose, you will raise or lower both the T4 and T3 as well.  The T4 and T3 in the “naturals” (Armour, Naturethroid, others) are like a matched set:  you can’t change one without changing the other.

This is important to realize, because not everyone can tolerate the same ratio of T3:T4.  I am an example of someone who is extremely sensitive to T3.  Raising T3 too fast, or having a T3 level much higher than my T4, created some pretty severe symptoms, as I’ve mentioned throughout this website and document.  As a result of this sensitivity, at best, I could tolerate 10% T3, and usually, it was less than that.  Only one grain, or tablet of Armour, already contains almost 20% T3 – way more than I can handle.  Consequently, I could not take any of the “naturals” for this reason, as they all had much higher percentages of T3 in them.   The two or three times I tried, the consequences were disastrous for me.

I certainly am not against NDT replacement, indeed, I wrote an entire paper on why using NDT and iodine may help some people not responding to T4 only replacement a couple of years ago for a few friends ( Armour Iodine Protocol).    However, despite the very vocal patients who believe that NDT is “for everyone”, I disagree with this blanket statement.   The facts are, thyroid conditions are incredibly complex, and there is not a “one treatment fits all”, whether that treatment be NDT or synthetic T4 alone.  If it were that simple, there wouldn’t be millions of dissatisfied, unhappy, and downright suicidal thyroid patients continuing to litter the internet.  I desperately wanted the NDT’s to work for me; I desperately wanted to be one of the many happy patient’s whose lives were completely turned around by it.  In my case, I gave the NDT’s more than the proverbial “old college try”, including trying to follow recommended protocols to make it successful.  I also felt I had enough knowledge to truly understand my approach, and despite my best cautions, ended up with catastrophic results the last time, forcing me off thyroid hormones altogether.


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