I sometimes wonder, how many of the things we commonly do or believe in the lab are based on verified and verifiable, objective data? A good way to find 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. Here are a few examples.
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, right? 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, where’s the data that proves that? Has anyone ever actually analyzed the glucose, or sodium, or potassium, in the first drop, the second drop, 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 a millennium 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”. Yet there is data to suggest that if the sample is to be analyzed within 30 minutes, room temperature is fine. There is also data to suggest that if you are going to put the sample on ice, you should collect in a glass syringe because there are different dynamics 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.
And a final lab myth: If glucose is not going to be run immediately it should be collected in a gray top tube because fluoride prevents glycolysis. This is not really a myth. Fluoride has been shown repeatedly to inhibit the enolase step of glycolysis, but does that really prevent loss of glucose in the sample? Most people are aware that even in grey top tubes, glucose concentrations will initially drop for the first 60 – 90 minutes. So is glycolysis inhibition really preserving glucose concentrations? A letter to the editor in 2008 showed clearly that although fluoride inhibits glycolysis almost immediately (no lactate production from zero time point), glucose continues to drop, even out to 90 minutes. The authors postulate that although glycolysis is blocked at the enolase step, glucose is still consumed by the cells because the glucose-6-phosphate which is formed at an earlier step than enolase can be routed to other pathways (3).
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? Or perhaps you have the data that truly demonstrates one or more of the above. Either way, I look forward to your comments.
- 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.
- Forsman RW. Why is laboratory an afterthought fro managed care organizations? Clin Chem 42(5):813-16. 1996.
- Mikesh LM, Bruns DE. Stabilization of glucose in blood specimens: mechanism of delay in fluoride inhibition of glycolysis. Clin Chem 54(5):930-32. 2008.