What do lab reference ranges really mean?

This question comes up frequently.

Here is what Labsonline has to say:

http://labtestsonline.org/understand...ranges?start=0

The "normal" ranges are averages taken from many people considered to be "normal". So therefore they are not really cast in stone!

We see this with B12 ranges... which go down very low to 200 as normal, which at that level there can be significant neuro symptoms and damage. The new ranges explained on medical websites for doctors continuing education, suggest the lower limit should be 400, in US and in other countries it may even be a bit higher...like Japan.

Also tests are only a snapshot window for that day. You might be slightly higher or lower because of some metabolic need the body is dealing with. Taken at another time, that test may show a different result. ANA testing vacillates like this.

Then there are lab issues. Quest diagnostics actually went public a couple years ago, confessing that an entire year's tests for Vit D were not accurate. They were using the wrong protocols for calibrating the instruments!

There can be factitious readings from mishandling blood samples. Potassium measurement is one that often results in false highs because mishandling causes the red cells to burst and dump potassium into the serum where it is normally not as concentrated.

So tests are not always to be relied upon completely. Wise doctors will retest, maybe several times to see if a result needs further examination. Some variations with a range may be temporary and changeable as well. A few points up or down may reflect laboratory technique and not really be diagnostic.