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Many decisions within healthcare are based on results from laboratory tests. These results all have an uncertainty, which can be either neglectable or large enough to affect the clinical assessment. In external quality assessment (EQA) the laboratories make independent observations on the same control sample, with values unknown for the participants. The results can be used to determine if quality improvement is needed. We present EQA data for laboratory tests with three different measurement scales; quantitative, ordinal and nominal. Results from EQA should be used in the discussions of quality in test results and necessary analytical performance specifications should be agreed upon.

When communicating results from laboratory investigations from the laboratory to the requesters and further between different information systems, it is important that the value as well as the unique identity and name of the laboratory investigation are correctly cited. A committee under the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC) and International Union for Pure and Applied Chemistry (IUPAC) has developed a systematic nomenclature for the correct classification of laboratory investigations. Each generic laboratory investigation is provided with a unique NPU code. The system is in use among approximately 30 different clinical laboratories in Sweden, and has capacity to be the common denominator of all laboratory investigations, and to be used as the identifier in various information systems. The NPU system for the Swedish laboratories is currently administered by EQUALIS and partly financed by the participating laboratories. Other ways of funding, of benefit for the whole health care sector, will be investigated.

In 2003, The National Academy of Clinical Biochemistry published a consensus monograph on thyroid tests (available via Internet from 2002). The document, a result of international collaboration, describes the pathophysiological background and clinical application of the measurements as well as principles for their technical performance. Of value, and of definite clinical relevance, is the detailed description of factors affecting the results in health and disease. However, we lack a description of the sometimes large differences in values obtained with different generally available methods, as well as a presentation of the occurrence and evaluation of analytical interference and related technical factors affecting results. Readers with little experience from quantitative measurement in the clinical laboratory, therefore, are not stimulated to obtain a better understanding of causes and evaluation of unexpected results.

In 1999 a new and simplified procedure for calibration of the Owren prothrombin time (Owren PT) assay was introduced in Sweden by the national external quality assessment scheme (Equalis). The new protocol allowed local calibration by means of lyophilised national plasma calibrators and expression of results as an international normalised ratio (INR). A two-year follow-up involving analysis of data from all laboratories that have returned results to Equalis is reported. There was a significant reduction in both between-laboratory and within-laboratory variation after the introduction of the new calibration procedure. For the larger hospital laboratories analysing external controls with INR > 2, the mean coefficient of variation (CV) was reduced from 9.1% to 5.6% (P < 0.0001). The corresponding results from smaller laboratories in the primary health care units showed a similar decrease in CV from 8.8% to 6.3% (P < 0.0001). This study shows that the Owren PT assay is well suited for INR calibration employing calibrant plasmas.