When is “abnormal” abnormal? Dealing with the slightly out of range laboratory result

The perception by users that results which lie outside our quoted reference ranges are “abnormal” and therefore require action results in additional testing and further investigation. It is also a source of worry for patients.

The use of population reference ranges is an inexact science that often does not consider age, sex, ethnicicity and other influencing factors, and, in a setting of multiple testing, also does not consider the statistical likelihood of generating results that are out of range purely by chance. No simple answer exists of what should be done with the “slightly out-of-range” results, although providing better information for laboratories, users and patients will help in the most appropriate action (or inaction) being taken.

One of the questions occupying a large proportion of the primary care in pathology reviews in this journal¹ is the isolated “slightly abnormal” result in an otherwise fit person presenting with non-specific illness or as a result of “well-person” screening. This is a common cause of telephone calls, letters and referrals to secondary care and one that presents laboratory medicine and the user with a dilemma.

An abnormal result, however apparently clinically unimportant, is also a cause of concern for the patient and is potentially the origin of a cascade of further investigations. Although the answers in the primary care best practice reviews in this journal deal with specific test groups, some general trends emerge, which call for a pragmatic approach to the out-of-range result and for some basic information to be more …