The importance of harmonising reference intervals
A reference interval (RI) is a common factor in reporting pathology laboratory results; it is used to transform a numerical value into clinically meaningful information. However, it is not commonly known that reference intervals can vary between laboratories, often meaning that similar numerical results can be interpreted differently in different laboratories. We spoke to Associate Professor Graham Jones, Chemical Pathologist at St Vincent’s Hospital in Sydney, to discuss the importance of harmonising reference intervals.
“Reference intervals are a very commonly used tool to help with interpreting numerical pathology results. They allow the person looking at the report to see whether the value of a measurement, for example a serum sodium or a blood white cell count, is within the expected range for a healthy person.
“The result of a pathology test is only useful if you can compare it with something, and one of the things that it is most commonly compared with is what you can expect to find in a healthy person – that’s what a reference interval tells you.”
Reference intervals appear on nearly every report; however, different laboratories may interpret the same data differently. The interpretation of individual patient laboratory test results depends on the reference intervals with which they are compared. Harmonisation of this aspect of pathology testing is therefore now being undertaken around the world.
“It is the responsibility of individual laboratories to put the reference intervals on the report for each of the tests; however, because the laboratories do this themselves, then what you commonly find is that the reference intervals vary between different laboratories. Harmonisation of reference intervals aims to remove any unneeded variation between laboratories, so we can be sure that the reports carry the same information for whoever is reading them.
“There are reasons that reference intervals should be different. For example, if a laboratory has a method which produces higher values than another lab's method, then the values in healthy people will be higher and the reference interval should be higher. Similarly, if the population is different, for example if the people in Melbourne have different kidney function than the people in Sydney, then those reference intervals should also be different. However, these variations can often be caused by complex things such as the statistics used, i.e. how laboratories have defined normality; where they have sourced their reference intervals from; or when those intervals were established. This variation makes the interpretation of results from different laboratories more difficult,” said Prof Jones.
Reading test results can be confusing for patients. With more people now having direct access to their pathology test results, especially with the introduction of My Health Record, the information needs to be clear. The reference interval against which the results are being compared is always included within the report, and it is important that patients only use the reference interval from the laboratory that performed the analysis, not from any other source.
“The importance of harmonising reference intervals is now recognised in many parts of the world. Australia has been leading the way in trying to address this issue and has now been joined by other countries, including Canada, the Netherlands and the UK.
“Reference intervals are not the only way that a laboratory test is interpreted. There will be other clinical decision points, for example, those used to diagnose diabetes, that might be assigned by expert bodies and international organisations. The medical literature and a doctor’s individual experience might also suggest what levels of a certain test might be found in a patient with a particular illness: for example, how high the creatinine is in someone that has kidney disease.”
The process of harmonising reference intervals is a huge undertaking, due to the complexity and the size and scope of the task. Australia has led the world in this important area of pathology testing, and the situation is now improving. Harmonised reference intervals have now been established for a number of commonly requested tests, and work continues to harmonise the reference intervals for more complex tests.
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This article appeared in the December 2018 Edition of ePathWay which is an online magazine produced by the Royal College of Pathologists of Australasia (http://www.rcpa.edu.au/Library/Publications/ePathway).
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