Seminar - Do clinicians use the concepts of biological variation and reference change values

23 February 2012

Full title: Do clinicians use the concepts of biological variation and reference change values (critical differences) when monitoring patients with laboratory tests?

Speaker: Adjunct Professor Sverre Sandberg, University of Bergen, Norway, Laboratory of Clinical Biochemistry, Haukeland University Hospital and Norwegian Quality Improvement of Primary Care Laboratories


Background The majority of laboratory tests are requested to monitor patients' condition and response to treatment. Laboratory monitoring can be performed using test results from a central laboratory, from instruments on wards, outpatient clinics, at the general practitioners' office or in the hands of the patients, e.g. self-monitoring of blood glucose, measurement of HbA1c or PT-INR monitoring. When patients are monitored a key clinical question is: Is this patient stable; i.e. does the test result reflect that no fundamental change has taken place in the patients┬┤ condition or does the test result indicate a clinically significant change that needs to be acted upon? Laboratory tests requested for monitoring purposes should be able to help clinicians answering these fundamental questions and guide management actions and treatment accordingly.

Interpretation of monitoring test results can be performed by use of the 'reference change value' (RCV) or critical difference concept which takes into account both the analytical and within-subject biological variation of the test. This presentation will focus on how clinicians monitor patients with different clinical conditions using laboratory tests, and to what extent they follow the concepts of reference change values (RCV) when making decisions about patient management.

Methods We circulated questionnaires (between 4 000 - 10 000) containing case histories to clinicians in Norway and in different European and non-European countries, including Australia. The case histories mimicked common clinical scenarios in general practice and investigated the interpretation of HbA1c, Hb, INR and urinary albumin (micro-albuminuria). We also estimated the within-subject variation for these constituents in healthy and diseased persons and compared these findings with the results from the questionnaires. Each participant received a feedback report where their own results were compared to that of their peers. In addition, to support evidence-based best practice some advice on how to monitor these conditions was given.

Results and Discussion Our international survey revealed that there is great variation in what critical differences (RCVs) physicians will react upon. We found that GPs usually react and make medical decisions on smaller changes than what one would expect if the RCV concept, based on analytical and biological variation, was used. A discussion about the clinical utility of the RCV concept and its limitations will be given as well as how RCV can be calculated in an unstable situation (e.g. pregnancy). A model for how the RCV concept can be expanded using likelihood ratios and post-test probabilities will be presented.

Hosted by Screening & Test Evaluation Program (STEP), School of Public Health

Time: 1 - 2pm

Location: Chemistry Lecture Theatre 4, University of Sydney

Contact: Jessica Frazer

Phone: 02 9351 5994

Email: 0e0837050d265866210325350c151243350c390615593632171c264c