Why reference ranges differ between labs

A reference interval describes the values measured in a reference group of people, usually the central 95% of them. It is a statement about that group and that measurement method. It is not a statement about what any one person's value means, and it is not the same thing as a clinical decision limit, a cut-off used to decide on action. The two are often confused, and laboratory scientists have written about the confusion for years.

• The method. Different analysers and reagents measure the same marker slightly differently, so each method has its own interval.
• The population. An interval can be set for a particular group, for example by age or sex. A lab may use its own reference group or adopt the manufacturer's.
• The conditions. Fasting, time of day and the type of sample can all change what is measured.
• The lab's choice. Labs verify or transfer intervals in different ways, and update them when a method or a reagent changes.

• Keep each report's range with its result. Do not copy a range from one lab onto another lab's results, or from the internet.
• Expect shifts when a lab changes method. A new analyser can move both the values and the range, so look at both before reading a change.
• Compare a value with the range from the same report. That is the only comparison the lab itself stands behind.

BiomarkerHQ never supplies a range of its own. Each result is stored with the range printed on its report, or with one you type in, and a result is labelled below, within or above only against that range. A result with no range printed is shown without a label. Charts draw the range from your report behind the values.