The use of error and uncertainty methods in the medical laboratory.

Error methods - compared with uncertainty methods - offer simpler, more intuitive and practical procedures for calculating measurement uncertainty and conducting quality assurance in laboratory medicine. However, uncertainty methods are preferred in other fields of science as reflected by the guide to the expression of uncertainty in measurement. When laboratory results are used for supporting medical diagnoses, the total uncertainty consists only partially of analytical variation. Biological variation, pre- and postanalytical variation all need to be included. Furthermore, all components of the measuring procedure need to be taken into account. Performance specifications for diagnostic tests should include the diagnostic uncertainty of the entire testing process. Uncertainty methods may be particularly useful for this purpose but have yet to show their strength in laboratory medicine. The purpose of this paper is to elucidate the pros and cons of error and uncertainty methods as groundwork for future consensus on their use in practical performance specifications. Error and uncertainty methods are complementary when evaluating measurement data.

External Quality Assessment Schemes in Latin America.

As professionals of the clinical laboratory we must generate clinically useful results, products and services for the patients' health care. Laboratories must participate in one or more proficiency testing (PT) or external quality assessment (EQA) programs as part of routine quality assurance. Nevertheless participating per se is not enough. There are critical factors to take into consideration when selecting a PT or EQA providers. In most cases the survey's providers offer assigned values obtained from consensus of results provided by the participants for comparison, it is critical to evaluate consistency of the comparison group before interpretation and decision-making.