Lab Myths: Do You Know Why You Do Things?

Do you ever wonder how many of the things we commonly do in the lab are based on verifiable, objective data? A good way to discover the practices that I call lab myths is to teach laboratory medicine. Any student worth his or her salt will ask you why you perform tasks a certain way, and occasionally you will be unable to locate a good reason. Examples of this type of common practice abound and the following paragraphs mention a few.

Why do you wipe away the first drop of blood from a finger or heelstick for most uses? Everyone knows wiping away the first drop is the correct way to do a capillary collection, because the first drop of blood is contaminated with disinfectant and/or tissue fluid or tissue, etc. That only makes sense. Okay. My question for you is this: where’s the data that proves that? Has anyone ever actually analyzed the glucose, or sodium, or potassium, in the first drop, then the second drop, then the third drop and shown that there is a statistically different result, enough that you should not use the first drop? Or is it a lab myth? We do it because it makes sense and we’ve done it for as long as anyone can remember and everyone does it, but I have been unable to locate any actual data to support the practice. (And if you ask a group of diabetics, most of them use the first drop!)

Here’s another example: Blood gas samples should be sent to the lab on ice to prevent sample degradation. This is another common lab practice that everyone “knows,” and with this one you can find supporting data in places. Yet there is also data to suggest that if the sample is to be analyzed within 30 minutes, ice is unnecessary. In addition, many of those early studies were done on blood gas samples collected in glass syringes. There is data to suggest that there are different dynamics in samples collected in plastic syringes (1). When was the last time you received a glass syringe in your laboratory? The last glass syringe I’ve seen was filled with Novocaine and coming at me at the dentist office.

A third lab myth: 60 – 70% of all medical decisions are based on laboratory test results (2). You can find this statistic quoted everywhere in laboratory medicine (Mayo, CAP, Modernising Pathology Services document on UK Department of Health website, IFCC, to name a few). I’ve always wondered where the data is that supports this assertion. Granted I agree that it makes intuitive sense that the majority of medical decisions are based on laboratory data, however, has anyone actually demonstrated it with supporting data? It also makes sense that 95% of all statistics are made up on the spot.

These lab myths are examples that illustrate a point. Sometimes what we “know” can cause us not to question things we should question, and investigations are not performed that should be performed. It’s a good idea to always question a long standing practice because, like in the blood gas example, conditions may have changed (Who still uses glass syringes?). So think about it. Do you have your own lab myths?

  1. Mahoney JJ, Harvey JA, Wong RJ, Van Kessel AL. Changes in oxygen measurement when whole blood is stored in iced plastic or glass syringes. Clin Chem 37(7):1244-48. 1991.
  2. Forsman RW. Why is laboratory an afterthought for managed care organizations? Clin Chem 42(5):813-16. 1996.


-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.

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