Is a Complete Blood Count Foolproof?

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Dr. Susan Leclair talks about the reality of foolproofing a CBC. She starts off by saying that no test is foolproof and is capable of being impacted by infinite causes. Among some of the factors to affect test results are wrong collection, a tight tourniquet on the test tube which can alter fluid balance, blood that pumps too slowly into the test tube due to low blood pressure, and broken equipment. Dr. Leclair states the most prevalent factor to cause inconsistent data comes from differentials found in 7,000 per microliter white cell counts. The same drop of blood examined by two physicians will show variations between polys and lymphs. Lastly, Leclair concludes that patients should understand variabilities are within levels of expectation, according to the conditions of the entire process.

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Transcript

Please remember the opinions expressed on Patient Power are not necessarily the views of our sponsors, contributors, partners or Patient Power. Our discussions are not a substitute for seeking medical advice or care from your own doctor. That’s how you’ll get care that’s most appropriate for you. 

Tamara Lobban-Jones:

Our question comes from Dan.  Some of the blood test results I get seem to be incorrect.  How often does this happen when looking at CBC results?  

Dr. Leclair:

Incorrect.  Well…

Tamara Lobban-Jones:

…or is the CBC foolproof?  I think that's really what we're getting at. 

Dr. Leclair:

Okay.  Sorry, Dan, and I feel badly about saying this because I'm going to say something about the laboratory.  No test is foolproof.  Every test is capable of being collected wrong.  I wanted to do a CBC on you and I put the tourniquet on too tight and then, I don't know, there was a fire alarm, and when I came back the tourniquet was still on, so I picked up an incorrect specimen from you because I altered the fluid balances by doing that. 

The blood came in too slowly.  It happens a lot with people with low blood pressure, and it started to clot within the test tube, so I'm not getting a whole blood free of blood clots specimen.  I'm getting one that's been altered.  So, yes, there are times when that will happen.  There are times when we are human.  I don't like to admit that.  Everybody who works in the laboratory is a little bit on the OCD side.  They want everything to be right, but could a machine go down?  Sure.  Could something happen?  Yeah.  We're trained to be able to recognize big differences, but maybe not always the little ones. 

Probably the biggest place in the CBC might be in the differential.  You might have, let's say, a 7,000 per microliter—yeah, a 7,000 per microliter white cell count.  Well, what's a microliter?  It's less than a drop, and you've got 7,000 cells there.  I take one drop, a smaller drop, actually of your blood, put it on a smear, I'm going to look at 100 cells.  Am I going to look at the same 100 cells that the person next to me is going to look at?  Maybe not.  Well, within that 100 cells I might get slightly more polys, and slightly fewer lymphs than the person sitting next to me.  So is it possible there's going to be a variability to these?  Yes.

What should happen is that the variability should be within levels of—of expectation.  If I were to—this is going to be a long answer.  I'll try and to it fast.  If I were to draw blood from you right now and run 10 hemoglobins, it's a chemical analysis, nothing should change.  I'm running 10 hemoglobins from the same test tube of blood.  I'm not going to get the same exact answer.  I'm going to get a variability that's going to be close.  If you're absolutely correct the answer is 15, it should be from like 14.6 to maybe 15.4.  It should be close, but it may not necessarily be exactly duplicative.  

Given that circumstance, every physician understands that there is a little give on either side of that answer.  And that sometimes causes people frustration because they'll look at a number, recognize that it's different from the last one, and have the physician say, oh, no, this is fine.  And what the physician is doing is saying it was a 15.4 before, it's a 15 now, there's really no technical, no statistical change in that.

Please remember the opinions expressed on Patient Power are not necessarily the views of our sponsors, contributors, partners or Patient Power. Our discussions are not a substitute for seeking medical advice or care from your own doctor. That’s how you’ll get care that’s most appropriate for you. 

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Page last updated on June 20, 2019