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Getting Everyone on the Same Page When Measuring Back Pain
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Posted on: 11/30/1999
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Pain is a subjective sensation. It can't be seen, photographed, or shown to someone in three-dimensions (3-D). That can create a dilemma when trying to measure this symptom to show improvement with treatment.
In the research world, studying low back pain and finding effective ways to treat it has become an international effort. Therefore, it's important that the main measure of results (reduced pain or pain relief) is reported the same from study to study. Consistent reporting of results makes it possible to compare study results and even combine the results of several studies to create a systematic review of the topic.
There are many different ways to measure pain. The simplest is asking a scale from zero (no pain) to 10 (worst pain) and ask the patient to give an objective (measurable) number to their subjective pain. This type of scale is called a numerical rating scale (NRS) or verbal rating scale (VRS).
Another example of a verbal rating scale is the Likert-type scale. In this type of scale, the patient pinpoints the pain intensity or severity using word descriptors such as no pain, mild pain, moderate pain, severe pain, or very severe pain. Each of these pain categories is divided into five separate levels of pain with equal distance between each pain item on the scale.
Another type of pain rating scale is the Visual Analog Scale (VAS). The VAS is made up of a straight line drawn on paper. The line can be drawn up and down (vertical) for patients who can't sit up or straight across (horizontal) for those who can be seated. In either case, the line is always 100 mm long (about four inches).
For a horizontal line (straight across), the left end represents "no pain" and the right end represents "pain as bad as it could possibly be" or "worst possible pain." When the line is presented in a vertical orientation (up and down) for the client who is lying in bed and cannot sit up for the assessment, "no pain" is placed at the bottom and "worst pain" is put at the top.
Any of these rating scales can be used to assess current pain, worst pain in the preceding 24 hours, least pain in the past 24 hours, or any combination the clinician finds useful. Both the Visual Analog Scale (VAS) and the Five-Item Verbal Rating Scale have been tested and shown to be reliable and valid. In other words, each time the VAS or the VRS scale is used by itself, it really does measure pain in the same way from patient to patient and from one time period to another for each individual patient.
That brings us to explain the purpose of this study. Many health care professionals use these two tests interchangeably as if they measure exactly the same thing. We know from other studies that the two tests are highly correlated. That means if someone has a high (or low) pain score on one test, they will also have a high (or low) score when given the other test.
But is the data collected from one test really the same as the other -- so that results from studies reporting one or the other can be considered equal? Do these two tests measure the same aspects of low back pain exactly alike? According to the authors of this study, no, they do not. Let's take a closer look at how they came to this conclusion.
One hundred and fifty-one (151) patients with lumbar degenerative disease participated in the study. They completed both scales before and after spine surgery. They used the scales to answer the question, How severe was your back pain in the last week? They also completed a number of other questionnaires to assess pain, function, and work status.
Using biostatistical analysis, the researchers were able to see that comparing the results obtained with one scale to the other did not yield equal results. For those readers who understand statistical analysis, you will be interested to know they came to this conclusion using a measure of disorder and level of concordance.
Basically, what this means is that using five-items on the Verbal Rating Scale (none to very severe) isn't the same as marking the 100 mm Visual Analog Scale (VAS) into five equidistant values.
In other words, a VAS between zero and three doesn't really mean the patient's pain level is "mild" as measured by the same distance on the Verbal Rating Scale. A VAS between three and six doesn't correlate to "moderate pain" on the VRS. And more than seven (severe pain) on the VAS doesn't match up with the higher categories of the VRS.
There is too much overlap of scores from one tool to the other to use them interchangeably as if they are measuring exactly the same pain levels. Once again, results like this point out the difficulty of measuring perceived pain. Some tools may make it easier to over- or under estimate severity of pain.
In summary, when using back pain as a measure of results of treatment, scientists around the world need a standardized outcome measure. Such a standard measuring tool would allow researchers to make international comparisons. The Visual Analog Scale (VAS) and the Verbal Rating Scale (VRS) may be used together but they cannot be used interchangeably as if what they measure is the same.
The authors offer one final note about their study. They point out that these results really only apply to people in a hospital setting undergoing spine surgery for severe low back pain associated with degenerative lumbar disease. The same results may be seen with patients in other settings like a primary care clinic or rehab unit and with patients who have less intense pain. But that conclusion isn't to be assumed without specifically studying those different parameters.
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References:
Antònia Matamalas, MD, et al. The Visual Analog Scale and a Five-Item Verbal Rating Scale Are Not Interchangeable for Back Pain Assessment in Lumbar Spine Disorders. In Spine. October 1, 2010.Vol. 35. No. 21. Pp. E1115-E1119.
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