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Knowledge

Understanding Laboratory Test Results

An educational overview of how laboratory results relate to reference information, method, specimen quality, and clinical context.

5 min read Laboratory Quality Assurance #specimen #time
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Learning Objectives

By the end of this resource you should be able to:

- Explain why laboratory results should not be interpreted in isolation.
- Distinguish reference intervals from clinical decision limits.
- Identify factors that can affect result meaning.
- Explain the importance of method and specimen context.
- Distinguish critical values from ordinary reference intervals.

Understanding Laboratory Test Results

Overview

A laboratory result is a measurement, observation, or finding produced by a defined examination procedure.

The result is one component of clinical information. Its meaning depends on the examination, method, specimen, patient, timing, and appropriate reference or decision framework.

Reference intervals

A reference interval describes the distribution of results observed in a defined reference population under specified conditions.

Reference intervals are not necessarily universal. They can vary with:

  • Population
  • Age
  • Sex or other biological characteristics where relevant
  • Specimen
  • Analytical method
  • Laboratory procedures
  • Statistical approach

LabGoTo's Reference Ranges section should therefore be used for dedicated reference information.

Clinical decision limits

A clinical decision limit is different from a reference interval. It is a threshold used for a particular clinical decision or purpose.

A result can therefore be outside a reference interval without automatically establishing disease, or fall within a reference interval without excluding a clinical condition.

Analytical context

When assessing a result, consider:

  • Method
  • Calibration
  • Quality-control status
  • Analytical measurement characteristics
  • Potential interference
  • Specimen quality
  • Units
  • Reporting conventions

Pre-analytical context

The result can also be affected by:

  • Patient preparation
  • Collection
  • Tube or container
  • Transport
  • Processing
  • Storage
  • Timing

Trends over time

Serial results can sometimes provide more useful information than a single measurement.

When comparing results, consider whether:

  • The same or comparable method was used
  • Units are the same
  • Specimen types are comparable
  • Timing is relevant
  • The laboratory reference framework changed

Critical or alert results

Some laboratories define critical or alert values that require prompt communication because they may indicate a potentially serious condition.

These values are laboratory- and policy-specific and should not be confused with ordinary reference intervals.

Interpretation and diagnosis

Laboratory results contribute to clinical decision-making but do not automatically constitute a diagnosis.

Interpretation should consider the clinical question, patient context, laboratory method, and other relevant findings.

Key points

  • A laboratory result should not be interpreted in isolation.
  • Reference intervals and clinical decision limits are different concepts.
  • Method, specimen quality, timing, and patient factors can affect interpretation.
  • Serial results require appropriate comparability.
  • Critical-result communication follows defined laboratory procedures.

References

  • World Health Organization. Laboratory Quality Management System: Handbook.
  • ISO 15189:2022. Medical laboratories — Requirements for quality and competence.