Published: 20 Apr 2025

The low and high reference ranges for blood tests can vary between labs due to differences in equipment, methodologies, and population demographics.
Here’s how they differ and how you can compare them effectively:

Why Do Reference Ranges Vary Between Labs?
Different Testing Methods and Equipment

Labs use various analyzers (e.g., Roche, Siemens, Abbott), each with unique calibration.

Example:

Creatinine (kidney function) may be measured via Jaffe method (higher range) vs. enzymatic assay (lower range).

Population-Based Adjustments

Some labs adjust ranges based on local demographics (age, sex, ethnicity).

Example:

Hemoglobin ranges differ for men (13.8-17.2 g/dL) vs. women (12.1-15.1 g/dL).

Units of Measurement

Some countries use mg/dL, others mmol/L (e.g., glucose, cholesterol).

Example:

Glucose → 70-99 mg/dL (US) vs. 3.9-5.5 mmol/L (Europe).

Lab-Specific Protocols

Fasting vs. non-fasting tests (e.g., triglycerides).

Time of day (e.g., cortisol peaks in the morning).

How to Compare Blood Test Ranges Across Labs?
1. Check the Lab’s Reference Range
Always refer to the lab-specific range printed on your report (e.g., "Normal: 0.6-1.2 mg/dL").

2. Look for Standardized Guidelines
Some tests follow universal standards:

HbA1c (diabetes): Standardized by NGSP (%) and IFCC (mmol/mol).

Thyroid (TSH): Most labs use 0.4-4.0 mIU/L, but some argue for narrower ranges.

3. Use Conversion Tools
For unit differences (e.g., mg/dL ↔ mmol/L):

Cholesterol: 1 mmol/L = 38.67 mg/dL.

Glucose: 1 mmol/L = 18 mg/dL.

4. Consult a Doctor for Interpretation
A value "normal" in one lab may be "high" in another.