Identifying and Reducing Pre-analytical Errors in the Medical Laboratory

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Medical laboratory professionals must comply with stringent and robust standards in all aspects of their daily activities. The set of standards to which a laboratory must comply will differ depending on the scientific discipline of the laboratory, however, ISO 15189:2022 – Medical Laboratories – Requirements for quality and competence, applies to all medical laboratories. This recent version of the standard introduces increased focus on risk stratification and mitigation for patients and laboratory stakeholders, placing more emphasis on quality control to improve the accuracy and validity of the results obtained.

In a clinical chemistry laboratory, as in others, internal quality control is of upmost importance. Internal quality control (IQC) is the process used to ensure that all results produced are accurate, reliable, and reproducible. To achieve this, a laboratory must carry out checks on the pre-analytical, analytical, and post-analytical phases of testing.

The pre-analytical phase of laboratory testing includes collection, handling, transportation, storage, and preparation of samples. Even when the highest level of care is taken to ensure that all aspects of the pre-analytical phase are suitable and correct, errors can occur, exhibiting the need for clear and efficient quality control processes.

As part of our Acusera quality control range, Randox has developed the Serum Indices quality control to aid in the detection of the common pre-analytical error’s haemolysis, icterus and lipemia, collectively known as HIL. HIL interference can have disastrous effects on the quantification of many analytes, and it is therefore vital to determine levels of interference to improve laboratory efficiency and reduce the frequency of erroneous results. Figure 1 shows a graph of wavelengths at which each of these interferents may affect assays and the table below describes these forms of interference:

 

Interference Description
Haemolysis The degradation of red blood cells causes interference between 340-440nm and 540-580nm. Red blood cells experience membrane disruption due to tangential stress which results in degradation of cellular integrity and the release of interfering cellular components such as haemoglobin, K+ ions  and aspartate aminotransferase. Haemolytic interference may be evident in assays such iron, lipase, albumin, and creatine kinase.
Icterus Interference as a result of high bilirubin concentrations, affecting assays measured between 400-550nm. The high bilirubin levels result in a yellowish pigmentation of the sample, caused by hepatic necrosis, sepsis, or several other conditions.  Most prevalent in neonatal departments, icteric interference can cause inaccuracies in assays for phosphate, creatinine, cholesterol, triglycerides, and uric acid.
Lipemia Interference caused by an aggregation of lipoproteins which affects the turbidity of samples. Lipemic interference can be cause by several mechanisms, the most common being the light scattering effect caused by aggregations of chylomicrons or other large forms of LDL. The larger the LDL molecule, the larger the lipemic effect.  Lipemic interference is evident in assays measured between 300-700nm, however, interference increases as wavelength decreases.

Classical determination of HIL interference took the form of a visual assessment. A sample was examined for tell-tale signs of one or more of these types of interference. However, these methods are subject to operator interpretation and lack harmonisation and uniformity across the industry.  These signs are detailed in the table below and illustrated in figure 2.

Interference Visual indicator
Haemolysis Red discoloration of serum samples which is directly proportional to the concentration of haemoglobin and other interfering erythrocyte components.
Icterus Yellow pigmentation of serum samples increases proportionally to the concentration of conjugated and unconjugated bilirubin.
Lipemia Increased sample turbidity proportional to lipid concentration.

Modern clinical chemistry analysers have onboard HIL detection capabilities which offer objective, semi-qualitative or qualitative analysis of these forms of interference in a more precise and consistent manner. Automation of HIL detection improves laboratory throughput along with test turnaround times and enhances the reportability of the results.

Errors at any stage of the analytical process will result in retesting of the sample. Errors in the pre-analytical phase can have repercussions such as increased cost of repeated sample collection and testing, poor test turnaround times, and more seriously, delayed or incorrect diagnosis causing an exacerbation in the condition of the patient. To add to the adverse outcomes on patients, repeated testing places additional stress on laboratory resources and staff which ultimately affects every aspect of a laboratory’s daily activities.

We hope that by using the Acusera Serum Indices quality control and EQA scheme we can help to improve the accuracy of laboratory testing around the world and remove some of the excessive strain placed on laboratories and the professionals who continually strive for the highest levels of quality in all their work.

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