Weighing in on Liquid Measurement Error

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December 5, 2014

By Bryan Feldmann, PharmD student

If someone were to ask you what the difference was between a teaspoon and a tablespoon, would you know what to say? You might have prescriptions from your doctor or medications you bought over-the-counter that tell you to take a number of tablespoons or teaspoons of the medication. A teaspoon will usually be abbreviated as “tsp” and tablespoon as “tbsp.” Because the two abbreviations look very similar, it can be easy to mix them up at a first glance. This can be a big problem, because it is so important that meds are taken exactly as directed.

You may already know what teaspoons and tablespoons are, but many people do not. Tablespoons and teaspoons are two different units of measurement. Similarly to gallons and liters, teaspoons and tablespoons are both used for determining how much volume something has (in other words, how much space it takes up). You will usually see units of volume used when your medication is a liquid.
So, how do these two similar units of measure differ? To begin, a teaspoon is smaller than a tablespoon. You can remember this by thinking of how big a table is compared to a cup of tea. In fact, tablespoons are three times larger than teaspoons. Now, just think about how dangerous it might be if someone accidentally took three times the amount of drug they were supposed to by mistake. According to a new study published by the American Academy of Pediatrics (medical care of children and teens) there are more than 10,000 calls to the poison control center every year because of errors patients made in how much of a liquid medicine they took.1 Just imagine the horror of the parents and caretakers being forced to call the emergency number because of an adverse reaction to a medication error. Since liquid medications are usually given to children, the study also specifically measured how many times parents made a mistake when pouring medicine for their kids. When they were supposed to measure with either teaspoons or tablespoons, they accidentally measured incorrectly 40% of the time, or 2 out of every 5 times!1 What can be done to fix this?

Teaspoon (tsp) and tablespoon (tbsp.) look so alike it is no wonder people can mix them up, but there is another common way to measure volume— the milliliter, or “mL.” A milliliter looks and sounds nothing like a teaspoon or a tablespoon, so it would stand to reason that people would not confuse it with anything else. There are 5 milliliters (mL) in a teaspoon, meaning there are 15 mL in a tablespoon.2 So milliliters are also useful for being more precise, since not everything must be in multiples of 5 milliliters. In another study, parents who had to measure medications in teaspoons or tablespoons were compared to those who measured in milliliters.3 The parents who were asked to use teaspoons and tablespoons were about twice as likely to make a mistake.3 287 single parents or pairs of parents were studied to get these results.3 This is a very small sample when compared to how many parents there are giving medications to children in the country, so more research should still be done.

Just mixing up the units is not the only reason these forms of measurement are so problematic, however. Many homes have kitchen teaspoons and tablespoons spoons just for measuring in teaspoons and tablespoons, but a study in the International Journal of Clinical Practice showed that the spoons that people have differ drastically from one another and are not accurate.4 Another study, published in the Archives of Pediatric and Adolescent Medicine, which is itself published by the American Medical Association, found that oral syringes and droppers are the best tools to use to measure volume and avoid error.5 300 parents were asked to measure out one teaspoon of acetaminophen with dosing cups, dosing spoons, oral syringes, and droppers. 70% of the parents made an error when it came to using the dosing cups with printed markings, and 50% made an error when using dosing cups with etched markings. More than a third of just these mistakes alone would have been highly dangerous overdoses if this study were not conducted in a controlled environment. According to the Institute for Safe Medical Practices’ reporting on this study, “Parents who make mistakes when using dosing cups are often confused about the differences between teaspoons and tablespoons.”6 Mistakes were only made 6% of the time when using a dropper, 10% of the time when using an oral syringe, and 14% of the time when using a dosing spoon. Keep in mind that a dosing spoon is different than a kitchen teaspoon or tablespoon, in that it is accurately calibrated to hold the amount it purports to, unlike the others, which have been shown to vary from spoon to spoon. So we can rest assured that it would be much safer to measure a number of milliliters in a liquid measuring device such as a dropper instead of simply trusting in one of these spoons. Additionally, it is not very easy to measure the exact amount of medication such that it is lying flat at the brim of the spoon without making a mess. This could be much easier if a dropper or oral syringe was used.

It would be great if milliliters replaced teaspoons and tablespoons on all drug labels over time, but at the moment we will likely continue to encounter all three units of measure. Armed with the knowledge of how much each unit represents and being careful when you’re reading instructions will decrease your chances of committing a liquid medication measurement error. As a future pharmacist, I would recommend always using a measuring cup or another device such an oral syringe over a spoon to measure tablespoons and teaspoons, even if the spoons say they are designed specifically for that purpose. Share these important tips with friends and family and always be careful in order to guarantee positive outcomes for yourself and your loved ones. And if you are a health care provider follow the link here to see ISMP’s recommendations for preventing liquid medication errors.

Have you ever mixed up tablespoons and teaspoons? Have you seen someone else mix them up? What steps will you take to avoid liquid medication mistakes?

References

  1. Schmidt C. Child medication measurements confuse parents. cnn.com  http://thechart.blogs.cnn.com/2014/07/14/child-medication-measurements-confuse-parents/. Published July 14th, 2014. Accessed November 6, 2014.
  1. Teaspoon v. tablespoon: What’s the difference? Ismp.org https://www.ismp/org/consumers/teaspoon.asp Updated 2014 Accessed November 6, 2014
  1. Yin H, Dreyer B, Ugboaja D, et al. Unit of measurement used and parent medication dosing errors. American Academy of Pediatrics. 2014;134(2).
  1. Falagas ME, Vouloumanou EK, Plessa E, Peppas G, Rafailidis PI. Inaccuracies in dosing drugs with teaspoons and tablespoons. Int J Clin Pract. 2010;64(9):1185.
  1. Shonna Yin H, Mendelsohn AL, Wolf MS, et al. Parents’ medication administration errors: role of dosing instruments and health literacy. Arch Pediatr Adolesc Med. 2010;164(2):181-186.
  1. Use an oral syringe or dropper to measure children’s medicines, not a cup.ismp.orghttps://www.ismp.org/newsletters/consumer/Issues/20100105.asp. Published June 2010. Accessed 12/02, 2014.

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Posted in: Pediatrics, Preventative Health