Published on May 17, 2017
What do lab tests reference ranges mean, and how are they established? Patient Power founder, Andrew Schorr, poses this question to experts Dr. Susan Leclair and Dr. William Wierda. Together, they delve into a deeper understanding of what your lab results mean and how they are interpreted.
Sponsored by AbbVie. Produced by Patient Power in partnership with AACC's Lab Tests Online and The University of Texas MD Anderson Cancer Center. These organizations have no editorial control Patient Power is solely responsible for program content.
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Transcript | How Are Lab Test Reference Ranges Determined?
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Okay. Now, Susan, I'm willing to bet that most of the people on this program when they—if they're given their blood test results back—and I would say always ask for that—we're going to have, depending upon the way the lab reports it—I know I get Hs and Ls all over the place. And it says the normal range, and I'm high or I'm low, this and that. It's kind of unnerving, but some of us have been living with this a long time. So what are the—what do the ranges mean, and how are those ranges established?
For every single test in every single laboratory, the laboratory staff must create a reference range, a range against which their physicians can compare their individual patients’ results to a population.
That means that very rarely are you ever going to get exactly the same reference ranges between two or three or five facilities. That causes trouble sometimes with people, but what we typically do is we want these ranges to describe the typically healthy person.
So if I'm going to be doing a test for hematocrits, I want a population of adult men, because that will reflect a certain kind of range, a population of healthy adult females, and maybe children or whoever else is in my local area that's going to be using my—my instrument. And the math that I use then will describe that 95 percent of all the healthy people that I tested fall within this number and this number.
That's what's defined as a reference interval or a reference range. It's a thumbnail handy thing to give to a physician. And the instruments, because they are computers, very dutifully will look at a 10.1 and say, oh, that's .1 higher than 10, it must be an H. Or it must be an L. I think physicians like Hs and Ls in some circumstances, but I suspect they are the bane of their existence in other areas, because Hs and Ls only mean that you have fallen in or out of what my reference range is. It doesn't mean that it is unhealthy or healthy for you. That's Bill's job.
What happens is I have to send the stuff to him, and he's the one who takes the number, the range, the H and the L if there is one, who you are, what you are, are you 17, are you 79? Are you, recently conquered Mt. Everest, or was the most important thing you've ever done was change a channel with your remote? He's the one who has to take all of that into consideration and make sense as to whether that H or that R is meaningful. So I'm going to turn the rest of this over to Bill to try and figure out, do you actually even look at Hs and Ls?
Yes. Well, yes, he's shaking his head. Bill?
No, I don't usually look at Hs and Ls, because I know the values that I expect, and I have in my own mind what the reference range is for a particular patient and for a particular diagnosis. So I pay less attention to the Hs and Ls, and sometimes an H or an L is okay for patients, for particular patients.
So, for example, if we're talking about a low hemoglobin, the hemoglobin may be slightly below the normal range, but that's okay for CLL in most situations. What we really pay attention to, or what I really pay attention to is the hemoglobin dropping, is it less than 10 or 11, and that's when I need to make a decision or have a discussion about treatment or what have you. So I have in my own mind what the reference—what my reference ranges are for a particular patients and diagnoses.