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What’s “Normal” in a Lab Range?

March 23, 2017

It is true that experience functional medicine practitioners often read conventional labs differently than the normal reference ranges suggest. This can be a bone of contention.

I like this analogy regarding lab interpretation and shoe size. Most labs define “normal” as the average result plus or minus two standard deviations. This covers about 90% of the “normal” population. If you were to use this standard to determine what the average shoe size was, it would probably be somewhere between 6 and 12. Given biological individuality, it becomes rather absurd to suggest that you could give any human being a shoe between size 6 and 12 and expect it to fit. In this way, conventional laboratory ranges can be seen as useful when determining if someone in a broad population selection is clearly experiencing a physiologic problem. However, when we have an individual in front of us with symptomology to consider, it pays to pay much closer attention to where that person falls within the conventional laboratory ranges.

Lab normal ranges
One example is thyroid stimulating hormone (TSH). Most conventional labs suggest that anything from 0.5 to 5.0 mIU/L is normal. However, there is substantial evidence from conventional governing bodies for over a decade to the contrary. The National Academy of Clinical Biochemistry recommended that the upper limit of TSH should be 4.0, while the American Association of Clinical Endocrinologists set the upper limit at 3.0, and other groups went as low as 2.5. The goal here is to help patients that were left out in the cold by a strict conventional interpretation of their lab results. I call these patients “medical refugees”, and one of the key missions in functional medicine is to identify and help these patients.

Another example is C-reactive protein (CRP) a marker of inflammation. Normal might be anything between 0.1 and 3.0. However, when I have a patient who is suffering from inflammatory symptoms or conditions of any kind, I like to see the CRP below 1.0, and I am likely to take measures to help decrease inflammation in these patients.

If I have a patient suffering from fatigue who is in the bottom 10% of the normal range for ferritin or serum iron, and they look pale, I’m not going to tell them that their iron levels are fine. I’m going to suggest that they take additional iron.

Whatever I am going through labs with the patient, I always look at where they live within the normal range in the labs that relate to their symptomology. It takes more time to do this, but the effort frequently pays off for the medical refugees who may have been neglected by a strict conventional medical interpretation and approach.

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