Slide 1
A range comes from comparison
A laboratory reference range describes results in a defined comparison population. It is a guide for interpretation, not a boundary between health and disease.
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Healthy people can have results outside a range, and people with illness can have results inside it. The meaning of a result depends on why the test was ordered.
Slide 2
Methods and people differ
Reference ranges can vary with laboratory methods and population characteristics. A number should be read with its units and the range supplied.
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A value copied without its unit can become misleading. The same concentration may be expressed on different numerical scales, so a larger-looking number is not automatically a larger biological quantity.
Slide 3
Preparation can influence a sample
Food, medicines and the conditions of collection can affect some test results. Laboratories specify preparation when it matters for interpretation.
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The relevant preparation differs among tests. A generic rule applied to every sample can be inappropriate, which is why the actual test instructions belong with the measurement.
Slide 4
A threshold may serve another purpose
A clinical decision threshold is chosen to guide a particular decision. It is not necessarily identical to a statistical reference boundary.
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A screening or treatment decision combines evidence about outcomes with the test value. Describing what is common in a reference population is a different task from deciding when an intervention helps.
Slide 5
Change can carry information
A series of results may show a pattern that one isolated measurement cannot. Comparability of methods matters when assessing a trend.
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A clinician may consider whether an observed change exceeds expected biological and measurement variation. A flag on a report starts interpretation; it does not finish it.
Sources
- How to Understand Your Lab Results
MedlinePlus Medical Test
- Laboratory Tests
MedlinePlus