Before any patient result can be confidently reported for patient care, a laboratory must confirm that the reference interval in use accurately reflects values expected from a healthy population.
Although reference intervals may be adopted from manufacturers or published resources, these may not automatically be appropriate to newly implemented analyzers or methods. Verifying reference intervals prior to routine patient testing therefore is a crucial step to ensure reliable clinical diagnosis.
What is a Reference Interval?
A Reference Interval is defined as the range of values expected from a healthy population. This is expressed as the central 95% of test results from healthy individuals, allowing lab results to distinguish between expected and potential health concerns.
A 95% reference interval is used because it offers a reliable and practical way to define what “normal” looks like in a healthy population. By focusing on the central 95% of results, labs capture most of the natural variation in biology while keeping the number of healthy individuals who fall just outside the range to a minimum.
When a laboratory adopts a reference interval from published sources including manufacturer claims, Clinical and Laboratory Standards Institute EP28 recommend verifying that these ranges works for your laboratory setting by testing healthy patient samples and confirming their results fall within the adopted range.
Reference Interval Experiment Design
- 20 healthy patient samples spanning the reference interval claim
Reference Interval Experiment Steps
Step 1 – Define Criteria for Healthy Individuals
- Establish an age range appropriate for the reference interval being verified
- Confirm health status: individuals should be asymptomatic and free of relevant chronic conditions
Step 2 - Prepare Samples to be used
- Collect 20 samples from individuals who meet the defined healthy criteria
Step 3 - Perform the Experiment
- Analyze the samples under routine laboratory conditions
Step 4 - Record and Compare Results
Document test results and determine how many values fall outside the claimed reference interval
Step 5 - Determine Reference Interval Acceptability
- The reference interval experiment is considered passed if no more than 2 out of 20 results fall outside the claimed interval
- Document all findings clearly for quality assurance and accreditation purposes
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