Different test results due to various factors

  • Letters
  • Monday, 24 Feb 2003

IK YEO -- President, Malaysian Association of Private Medical Laboratories, Kuala Lumpur writes:  

WE REFER to the letter, “Medical tests highly inaccurate’’ by Consumers Association of Penang president S.M. Mohamed Idris, (The Star, Feb 13). 

He reported laboratory test findings after sending urine and blood samples to five laboratories in Penang. 

Before commenting on his sweeping statements and conclusions, let us put the matter in the right perspective by understanding the following critical facts: 

·A LABORATORY test result can only be as reliable and accurate as the “integrity’’ and/or “representativeness’’ of the sample submitted; 

·VARIATIONS in laboratory test results are inherent and accepted; and 

·MODERN medical practice cannot do without laboratory investigations. 

It is highly inaccurate and misleading for CAP to conclude that medical tests are highly inaccurate just because results differ from one laboratory to another without taking into account the following: 

·WERE the samples taken at one go or more than once from the person concerned, put into five bottles and sent to five different laboratories? 

·TREATMENT of the samples so collected such as handling, storage and transportation to the laboratories; 

·EQUIPMENT and test methodology used. 

Firstly, proper sample collections would be crucial. Secondly, any variation in treating the five sets of bottles, like excessive shaking, subjecting them to varying temperatures at any stage or taking a longer time to deliver a particular set to a particular laboratory all contribute to variations of the results. 

One needs to keep in mind that both blood and urine samples are quite labile; they deteriorate quickly, especially in tropical Malaysia. 

It must also be noted that laboratories invariably employ different methods to analyse the sample for identical tests. 

For example, Laboratory A uses method X to analyse for liver enzyme SGPT and reports a result of 15 IU/L at the same time quoting the normal range as 2-35.  

Laboratory B uses method Y for the same test and gets a result of 30 IU/L together with a normal range of 15-55.  

Even though the results may appear grossly different, both results fall within the respective normal ranges indicating that both are normal! 

A further point is that blood from the same person but taken at different times can produce varying results for identical tests even performed by the same laboratory, let alone different ones. 

Blood sugar and lipids, for example, can vary significantly between a fasting sample and one collected after a hearty meal. 

Turning now to comparison of test results from different laboratories and subsequent interpretation, the norm is to use a statistical analysis to arrive at the sample means and standard deviations for each result, ignoring “spurious’’ or “rogue’’ at both extremes. 

This is only possible when the sample “population’’ is large enough and more meaningful if the same equipment/methodology is employed. 

The former condition is definitely not met (with a population of five) and the latter very likely as well in the CAP survey. 

Finally, we are already aware that modern healthcare has been transformed from one of diagnosis, symptomatic treatment and cure to that of prevention (screening), maintenance and health enhancement. 

Thus the increasing critical role of laboratory investigations for health monitoring and clinical support, despite the inherent variations is within acceptable limits. 

As regards regulation of medical laboratories through a Pathology Act, the Malaysian Association of Private Medical Laboratories has already provided our inputs to the Health Ministry. 

We would definitely welcome this legislation and trust that it would clearly define the respective complementary roles of each stake-holder, including “consumers’ right for self-requests based on informed decision’’. 

At the same time MAPML has always been encouraging medical laboratories to seek accreditation to international standards in preparation for the Act. 

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