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Chapter: Biology of Disease: The Nature and Investigation of Diseases

Quality of Test Results and Clinical Auditing

The results of tests performed in pathology laboratories assist with diagnosis of disease or the monitoring of treatment.


The results of tests performed in pathology laboratories assist with diagnosis of disease or the monitoring of treatment. Thus they can greatly influence the management of patients, and it is essential to assure the quality of laboratory results. Erroneous results have the potential to cause considerable harm (both physical and psychological) to patients and must be avoided. All laboratories have practices and procedures to ensure erroneous results are minimized and that good quality results are provided. Errors can arise at the three different stages of analysis, that is, preanalytical, analytical and postanalytical. Preanalytical errors occur before the sample has been analyzed. Analytical errors arise during the laboratory testing procedure. Postanalytical errors arise after the specimen has been analyzed.


In general, preanalytical mistakes result from inappropriate methods of collection or incorrect labeling, handling, transport or storage of the specimen. Experimental mistakes that can give rise to analytical errors are detected by introducing systems for each clinical test to warn when errors occur. This is normally achieved by analyzing a control sample within each batch of tests. A control sample is one that is identical in composition to the test samples except that it contains a known concentration of the test analyte. All samples, including the control sample, must be treated identically. For example, if the concentration of glucose in serum is being determined, then the control should be serum, not water, containing a known concentration of glucose.

The control sample is usually an aliquot from a larger sample for which the mean and standard deviation have already been determined. The results for control samples are usually recorded graphically so that changes in the quality of the method are detected as soon as they arise. A common chart used for quality control purposes is the Levey-Jennings chart (Figure 1.22) in which the control limits are set at the mean ± 2 SD and ± 3 SD. If the control values fall outside the ± 2 SD limit, that is, there is drift away from the accepted limits, there is only a 5% probability that the result lies in a normal distribution around the mean and is still valid. Any results that lie outside the 3 SD warning limit suggests that a problem is occurring with the method. Problems could include unstable reagents in the analyzer, problems with temperature control or contamination, all of which require investigation. Occasionally there are gross (and usually very obvious) inaccuracies in the value of a test result such that it bears no resemblance to values seen in health or disease. These are referred to as ‘blunders’. Blunders usually arise because of transcriptional errors in reporting the result. To reduce the number of blunders, results should be checked thoroughly by senior staff before being sent to clinicians.

Most laboratories have their own quality control samples and these are used for internal quality assurance purposes. Many countries now participate in external quality assurance, whereby quality control samples are sent to participating laboratories from a central source to assess the analytical performance of their methods for particular analytes. Furthermore, to ensure quality of service provision, many laboratories follow a set of procedures required for accreditation by external agencies. These procedures ensure good laboratory practice (GLP) and cover all aspects of the laboratory that are involved in the production of test results. These procedures ensure that all laboratory staff are adequately trained and have clearly defined responsibilities. The equipment used should be of adequate standard with a logbook showing a full record of maintenance and faults. All methods used in the laboratory are standardized, fully documented and appropriate for the analysis. Full details of each method are provided as a standard operating procedure (SOP) that includes details of specimen handling, the analytical method, equipment used and quality control procedures.

To improve the quality of the services they provide, many laboratories participate in some form of audit. Clinical audit (Figure 1.23) is a process whereby practices and procedures involved in patient care are monitored and, if necessary, revised to provide a more efficient and cost-effective service that should ultimately benefit the patient. Audit is part of the process of ensuring

quality and is usually divided into five stages. The first is the observation and review of current practice and procedures in the laboratory. The second stage involves the identification of areas of concern that could be improved and questions are asked as to whether the current service can be provided more economically. Third, a series of changes are devised to rectify and improve the identified area(s) of concern. Fourth, these changes are implemented and steps taken to ensure compliance and, finally, at the fifth stage, the changes are monitored and compared with previous procedures in order to assess whether there is indeed any improvement in the service provided or whether the revised procedures are actually more cost effective.

A clinical audit is usually followed by a re-audit after an appropriate period of time. The audit may include several processes such as the initial stages of test requesting, specimen collection and transport. The audit may wish to investigate whether appropriate advice is available to clinicians requesting tests, whether the test request forms are easy to use or whether appropriate containers are provided for specimen collection. Other types of audit processes may relate to the analytical service provided by the laboratory, such as whether the repertoire of tests offered is appropriate to the needs of the clinical service. A clinical audit may wish to investigate whether provision of the laboratory service out of hours is efficient and cost-effective and whether test results are being returned to the clinicians at the right place and within an appropriate time.

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