Why do laboratories have different reference ranges, and is it appropriate to use Henry's textbook reference ranges instead of the laboratory-specific ranges?

Why Laboratories Have Different Reference Ranges

You should always use the laboratory-specific reference ranges that performed your patient's test, not Henry's textbook ranges, because each laboratory's reference intervals are validated for their specific analytical methods, patient populations, and local demographics. 1

Why Reference Ranges Differ Between Laboratories

Technical and Methodological Factors

Laboratories have different reference ranges due to multiple technical variables that affect test results:

• Different analytical platforms and methods: Even for the same analyte, different manufacturers' instruments use different antibodies, calibration materials, and detection methods, producing systematically different numerical results 2, 3
• Lack of standardization: Many analytes (particularly immunoassays) lack primary reference materials that are commutable across all commercial methods, leading to substantial discrepancies between platforms 4
• Specimen type variations: Whether plasma versus serum is used, or different anticoagulants, affects measured concentrations 1

Population-Specific Factors

Reference ranges must reflect the specific demographics of the laboratory's patient population 1:

• Age, sex, and physiologic state significantly affect normal values
• Ethnicity influences certain analytes (e.g., CK-MB shows 2-3 fold higher concentrations in African Americans versus Caucasians) 4
• Geographic and seasonal variations exist
• Local health characteristics of the population served

Regulatory Requirements

CLIA regulations explicitly require each laboratory to establish reference ranges appropriate for their specific patient population and analytical methods 1. Laboratories must either:

1. Establish their own ranges by testing ≥120 healthy individuals from their population
2. Verify manufacturer or published ranges using their own patient specimens
3. Adopt published ranges only if appropriate for their population, with ongoing monitoring 1, 5

Why You Should NOT Use Henry's Reference Ranges

Critical Pitfalls of Using Textbook Ranges

Using Henry's or other textbook reference ranges instead of laboratory-specific ranges can lead to patient misclassification and inappropriate clinical management 2, 3:

• Method bias: Studies show that 25% of chemistry tests and 38% of immunoassay tests have upper or lower reference limits >20% different from manufacturer ranges 2
• No overlap scenarios: In extreme cases, one laboratory may flag a result as "low" while another considers the identical value "high" (e.g., hemoglobin 13.8 g/dL in women) 3
• Narrow versus wide ranges: Laboratory-derived ranges for electrolytes like sodium (138-144 mmol/L), potassium (3.8-4.9 mmol/L), and chloride (102-110 mmol/L) can be considerably narrower than published harmonized ranges 2

Evidence of Better Clinical Outcomes

Stratified, laboratory-specific reference ranges are more closely associated with postoperative outcomes than generic published ranges 6. When laboratory-specific ranges differ from standard ranges, the laboratory-specific ranges better predict:

• Acute kidney injury (AKI)
• Postoperative mortality
• Other adverse outcomes (P < .001)

The 5% Problem

By statistical definition, reference ranges (typically the central 95% of healthy individuals) will label 5% of healthy people as "abnormal" 7. Using inappropriate reference ranges from textbooks compounds this problem, potentially flagging even more healthy patients as abnormal or missing truly abnormal results.

Best Practice Algorithm

Follow this approach for interpreting laboratory results:

1. Always use the reference range printed on the laboratory report - this is validated for that specific method and population 1

2. If comparing results between laboratories, recognize that absolute values may not be directly comparable due to method differences 4

3. For clinical decision-making, focus on:

   • How far outside the reference range the value falls (not just "high" or "low")
   • Serial trends in the same laboratory
   • Clinical context and pretest probability
   • Whether the laboratory has stratified ranges by age, sex, or ethnicity when appropriate 4, 6

4. When laboratories change methods or platforms, expect reference ranges to change - this is appropriate and necessary 1

Special Considerations

Common caveats to avoid:

• Pediatric populations: Most laboratories rely on external sources for pediatric reference intervals due to difficulty obtaining samples from healthy children 3. Extra caution is warranted here.

• Highly variable analytes: For tests like TSH or ferritin, method-specific differences are particularly pronounced 2. Gender stratification for ferritin is essential (males: 29-441 ng/mL vs females: 8-193 ng/mL in one study) 2.

• Cardiac biomarkers: The 99th percentile cutoff for troponins varies 13-fold between different assays 4. Using the wrong reference limit could miss or overdiagnose myocardial infarction.

The laboratory performing your test has validated their reference ranges according to regulatory standards for their specific analytical system and patient population - textbook ranges have not undergone this validation for your specific clinical context 1, 5.