Critical lab results – do they need to be repeated before reporting?

It is mandated that clinical laboratory staff should identify patient results that are grossly abnormal and have critical significance, so that clinical care staff can be informed immediately. Most laboratories have a policy of repeating the analysis before reporting such critical values in order to confirm that the result is valid and not simply an analytical error – but is this really necessary? 

Perhaps the inevitable delay in reporting critical values that flows from this repeat analysis policy can adversely affect patient care? These issues are addressed by the most recently published Q-probe study from the American College of Pathology. 

The authors of this study reasoned that because of the advances in analytical technology and sophistication of modern analyzers, the chances of analytical error is now so small that repeat testing is no longer necessary. Their study/survey, which involved the participation of 81 US laboratories and five laboratories outside the US, was designed principally to test this hypothesis.

Each participating laboratory was asked to submit 40 initial and repeat critical test results for each of the following four analytes: glucose; potassium; white blood cell count; and platelet count. For each of these paired results, timings of first identifying the result as critical and reporting the result were recorded. 

Also for each pair, participants were asked whether the repeat test result was judged still to be a critical value and whether it was judged to be ”significantly different”. In order to gauge the generality of policy surrounding critical values and their reporting, participating laboratories were asked a number of other questions.

In summary, analysis of submitted data revealed ”excellent” agreement between initial and repeat test results. For example, only 0.3 % of glucose paired results were judged to be ”significantly different”, and in more than 99 % of cases repeat testing did not change the judgment that the initial result was indeed a critical value. 

Repeat testing was found to delay reporting by 10-14 minutes in 25 % of laboratories and by 17-21 minutes in 10 % of hospitals. Twenty percent (20 %) of laboratories reported at least one instance during the previous year of clinical staff informing the laboratory that delay due to repeat testing had adversely affected patient care. 

The results of this study persuaded the authors to conclude that repeat testing is ”unlikely to be clinically useful and may adversely affect patient care”. The survey part of the study usefully reveals the extent of variability between laboratories with regard to the detail of repeat critical testing policy/practice.