Things to be Considered in Laboratory Testing: A Glimpse into the ‘Normal’ or Reference Range

By Rawaz Sulaiman:

Generally speaking, laboratory tests have become a common way that any individual would accept to get some information about their health status. In fact it is a good way to get some evidence about any dubious cases. Approximately 80% of physicians’ medical decisions for diagnosis are based on information provided by lab reports. Ideally, all medical information, including lab test results, can only be interpreted and understood once they have been put together in one piece. According to The Butterworth Medical Dictionary diagnosis is ‘’ the art of applying scientific method to the elucidation of the problems presented by a sick patient’’.

Routinely, for instance, when blood is taken for examination, there are a number of elements in the blood to be looked at. Each of these elements can be measured and the results are compared with the reference range to see how close they are to it. Commonly, high levels of cholesterols and triglycerides are among those elements of the blood that most concern people. Ultimately, people with high levels of these two elements, for example, will be at risk of gaining weight and cardio-vascular diseases (heart diseases). Some people are concerned about having a high level of what they called ‘blood fat’, which is scientifically referred to as triglyceride. They mostly blame lifestyles of insufficient movement and exercise and using cars instead of walking. Basically, what they are worried about is that their levels of triglycerides are high compared with the reference range.

You may have experienced a moment when your doctor tells you ‘’your test was out of the normal range’’, handing you a sheet of paper with numerous test results, which looks like it contains all the necessary information about your health status. You may start panicking in fear that you are really sick. But what does ‘’out of the normal range’’ mean? Is it a cause for concern? At that stage, the simple answer is, presumably, that further examination is required.

At this point, it is worth asking what is ‘normal’ or reference range? Where has it emerged from? How is it is established? Reference range is not something that was discovered and placed in the text books as an equation or standardized ratio to refer back to whenever you want. In fact, it is originally taken from testing millions of healthy people over a long period of time.

Experts have set a number of criteria for conducting such trials. Participants in these experiments are grouped based on their age, sex, ethnic origin, pregnancy and genetics. Exclusion of some participants may occur due to risk factors such as obesity, hypertension, genetic pre-disposition to particular diseases, smoking, alcohol consumption and the use of contraceptive drugs. Or it could be due to physical variations such as excessive exercise in pregnancy and stress.

Manipulating such a huge data in trials requires a well-designed program.  After that, analysis of the results is performed, mostly, through statistical analysis such as using parametric or non-parametric tests, depending, largely, on how the data are distributed alongside working out mean and standard deviation.

The use of reference range is quite controversial. Some labs are using a particular reference range belonging to their own surrounding regions. On the other hand, other labs may establish their reference ranges based on studies undertaken many years ago, when both the methods of conducting related studies and the population samples were different. This may apply to our system in Iraqi-Kurdistan.  

It would be an imaginative approach if setting up one’s own reference range is proposed. But the more appropriate solution could be the one that has been established by the Clinical and Laboratory Standard Institute (CLSI). According to this institute, if running clinical trials is difficult to perform, verifying the reference range that is provided by other laboratories is a good alternative. This approach is somehow easier to do, as it requires a small number of healthy people, around 20.

In a nutshell, the reference range is not a stable equation; it is changeable and there are always individual and batch-to-batch variations. So, it is quite crucial to look for other evidence in any dubious case.

Rawaz Sulaiman has an MSc in Biomedical Sciences from Sheffield Hallam University, UK.

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