Why Different Laboratories May Produce Different HTMA Results

Why two HTMA reports may not look identical

Receiving two different-looking HTMA reports does not necessarily indicate that one laboratory has made an analytical error. Several independent variables influence the final laboratory result. These include:

• sample preparation procedures
• washing protocols
• digestion methodology
• analytical instrumentation
• calibration standards
• laboratory quality control
• reference intervals
• interpretation methodology

Even when two laboratories analyse hair collected from the same individual, differences in one or more of these stages may influence the reported concentrations of individual elements.

This is not unique to HTMA. Many areas of laboratory medicine require laboratories to establish their own validated analytical methods while operating within recognised quality standards. Consequently, small analytical differences between laboratories are expected rather than exceptional.

See HTMA Testing Options: A Comparison of Leading Laboratories for an overview of internationally recognised HTMA providers.

Why consistency matters

For individuals monitoring mineral patterns over time, consistency is often more important than comparing reports from different providers.

When follow-up samples are analysed by the same laboratory using the same methodology, changes observed over time are more likely to reflect biological variation rather than methodological differences.

For this reason, many laboratories recommend using the same provider for repeat HTMA testing whenever long-term monitoring is the objective. Related reading: Why Interpretation Quality Matters More Than the Raw Numbers.

Sample preparation and washing protocols

Before elemental analysis begins, every laboratory must prepare the submitted hair sample. This stage is one of the most important contributors to analytical consistency.

Hair may contain external contamination originating from:

• dust
• sweat
• cosmetic products
• swimming pools
• environmental pollutants
• occupational exposure

Because laboratories aim to measure elements incorporated within the hair shaft rather than contaminants adhering to its surface, washing protocols play a critical role.

Different laboratories use different combinations of:

• detergents
• organic solvents
• ultrapure water
• sequential washing procedures

The objective is always the same: to remove external contamination while preserving endogenous mineral content. However, washing hair too aggressively may remove naturally incorporated elements, while insufficient cleaning may leave external contaminants behind.

Finding the appropriate balance has been the subject of scientific discussion for decades. This explains why laboratories using different validated washing protocols may report slightly different elemental concentrations.

Standardisation remains challenging

Unlike many routine blood analyses, no universally adopted international washing protocol exists for HTMA. Individual laboratories therefore validate their own procedures based on published research, internal quality assurance and accumulated analytical experience.

This does not necessarily mean one protocol is universally superior. Rather, it reflects the complexity of analysing biological samples that are continuously exposed to the external environment.

Laboratories with long-term analytical experience generally develop highly standardised preparation procedures designed to maximise reproducibility while minimising contamination-related variability.

Related reading: How Laboratories Prepare Hair Samples for HTMA and What Hair Tissue Mineral Analysis Can and Cannot Show.

ICP-OES vs ICP-MS: Does the instrument explain the difference?

One of the most common assumptions is that differences between HTMA reports are primarily caused by the analytical instrument used by the laboratory. In practice, the answer is more nuanced.

Most modern HTMA laboratories use either Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) or Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Both technologies are internationally recognised analytical techniques capable of accurately measuring trace and major elements in biological samples when operated under validated laboratory conditions.

ICP-MS generally offers lower detection limits for ultra-trace elements, whereas ICP-OES provides excellent precision for the concentration ranges commonly encountered in Hair Tissue Mineral Analysis. For routine HTMA, both analytical methods are capable of producing reliable elemental measurements.

The analytical instrument itself is therefore only one part of the overall laboratory process. Equally important are:

• sample preparation
• digestion procedures
• calibration standards
• instrument maintenance
• quality assurance
• operator expertise
• interpretation methodology

Two laboratories using the same analytical instrument may still produce different reports if any of these variables differ. Likewise, two laboratories using different instruments may obtain highly comparable results when standardized analytical procedures are followed.

For a deeper comparison, see ICP-OES vs ICP-MS in Mineral Analysis.

Laboratory reference ranges

Another important reason HTMA reports differ is the use of laboratory-specific reference intervals. Reference ranges are not universal.

Each laboratory establishes its own intervals based on factors such as:

• reference populations
• analytical methodology
• historical laboratory data
• statistical validation
• quality assurance procedures

As a result, the same measured calcium concentration may appear "within range" in one laboratory while being reported as "above reference" in another. This does not necessarily indicate disagreement between laboratories. Rather, it reflects differences in how reference intervals have been established.

Readers should therefore avoid comparing numerical values against reference ranges from different laboratories. The most meaningful comparison is usually between results generated by the same laboratory using the same analytical methodology.

Interpretation methodology

Analytical measurements represent only the first stage of an HTMA report. The second stage — interpretation — is often where laboratories differ the most.

Some reports focus primarily on numerical concentrations. Others place greater emphasis on:

• mineral relationships
• calculated ratios
• long-term mineral patterns
• nutritional context
• toxic element exposure
• educational explanations

Although laboratories may analyse identical elemental concentrations, the interpretation provided to the reader can vary considerably depending on the methodology used.

Modern evidence-based interpretation generally aims to:

• explain what laboratory findings may indicate
• acknowledge scientific limitations
• distinguish established evidence from hypotheses
• avoid deterministic conclusions
• encourage interpretation alongside clinical information

Reports that explain uncertainty and context are often more useful than reports that simply classify values as "high" or "low." Related reading: Why Interpretation Quality Matters More Than the Raw Numbers and Can HTMA Diagnose Disease?.

Quality assurance and laboratory standards

Reliable HTMA results depend not only on analytical technology but also on laboratory quality systems. Professional laboratories typically implement multiple layers of quality assurance designed to improve analytical consistency.

These commonly include:

• certified reference materials
• routine calibration verification
• internal quality control samples
• instrument performance monitoring
• analytical reproducibility testing
• documented laboratory procedures

Quality assurance reduces analytical variation and helps laboratories maintain consistent performance over time. It is important to recognise that quality assurance extends far beyond the analytical instrument itself. Every stage of the laboratory workflow contributes to the overall reliability of the final report.

Laboratory experience

Long-term analytical experience can also contribute to consistency. Laboratories that have performed HTMA for many years often refine:

• sample preparation procedures
• contamination control
• analytical workflows
• interpretation frameworks
• report structure

This accumulated experience may improve internal consistency between successive reports, particularly for individuals undergoing repeated testing over several years. Experience alone, however, should always be considered together with transparent laboratory methodology and appropriate quality assurance practices.

Why comparing reports from different laboratories is difficult

People occasionally submit samples from the same individual to two different laboratories expecting identical reports. In reality, identical reports should not necessarily be expected. Differences may arise from:

• sample preparation
• washing methodology
• analytical instrumentation
• calibration procedures
• laboratory reference intervals
• interpretation systems
• reporting style

For this reason, comparing reports line-by-line may lead to misleading conclusions. The more appropriate question is not whether every numerical value is identical, but whether each laboratory follows a standardized analytical process capable of producing internally consistent and scientifically defensible results.

When monitoring mineral status over time, changing laboratories may introduce methodological variation that makes longitudinal comparison more difficult. Whenever possible, repeat testing should therefore be performed using the same laboratory and comparable sampling procedures.

Related reading: HTMA Testing Options: A Comparison of Leading Laboratories and HTMA vs Blood Mineral Testing.

Example of a standardized HTMA testing workflow

While analytical instrumentation is an important component of Hair Tissue Mineral Analysis, consistency depends on the entire laboratory workflow rather than on a single technology.

A standardized HTMA process typically includes:

• standardized sample collection guidelines
• validated washing procedures
• controlled sample digestion
• ICP-OES or ICP-MS elemental analysis
• routine calibration and quality control
• laboratory-specific reference intervals
• structured interpretation methodology
• educational reporting

When all of these components are integrated into a consistent analytical workflow, laboratories are better positioned to provide reproducible results suitable for long-term monitoring.

Readers interested in seeing an example of an international HTMA testing service using a standardized laboratory workflow can find additional information here: International HTMA testing service. This resource is provided as an example of how an international HTMA testing workflow may be organized, including laboratory analysis and structured educational reporting.

Conclusion

Different HTMA laboratories may produce reports that appear different while still following scientifically valid analytical procedures. Variation may arise from:

• sample preparation
• washing protocols
• analytical methodology
• calibration procedures
• laboratory reference intervals
• interpretation systems
• report presentation

Understanding these factors helps explain why direct comparison between reports from different laboratories is often inappropriate. Rather than focusing on isolated numerical differences, readers should consider whether a laboratory demonstrates:

• standardized analytical procedures
• transparent methodology
• quality assurance
• evidence-based interpretation
• consistency across repeated analyses

For individuals monitoring long-term mineral patterns, remaining with the same laboratory is generally the most reliable approach for evaluating biological change over time.

Frequently Asked Questions

Further Reading

• What Hair Tissue Mineral Analysis Can and Cannot Show
• HTMA Testing Options: A Comparison of Leading Laboratories
• ICP-OES vs ICP-MS in Mineral Analysis
• How Laboratories Prepare Hair Samples for HTMA
• HTMA vs Blood Mineral Testing
• Why Interpretation Quality Matters More Than the Raw Numbers
• Can HTMA Diagnose Disease?
• International HTMA testing service

References

1. Kempson IM, Lombi E. Hair analysis as a biomonitor for toxicology, disease and health status. Chemical Society Reviews. 2011.
2. Pozebon D, Scheffler GL, Dressler VL. Hair as a biomonitor in human exposure studies. Analytical and Bioanalytical Chemistry. 2017.
3. Mikulewicz M, Chojnacka K, Gedrange T, Górecki H. Reference values of elements in human hair: A systematic review. Environmental Toxicology and Pharmacology. 2013.
4. Bass DA, Hickok D, Quig D, Urek K. Trace element analysis in hair: Factors determining accuracy, precision and reliability. Alternative Medicine Review. 2001.
5. Seidel S, Kreutzer R, Smith D, et al. Assessment of Commercial Laboratories Performing Hair Mineral Analysis. Journal of the American Medical Association (JAMA).
6. World Health Organization. Trace Elements in Human Nutrition and Health.
7. International Atomic Energy Agency. Human Hair Reference Material for Trace Element Analysis.
8. CLSI. Defining, Establishing and Verifying Reference Intervals in the Clinical Laboratory.
9. EFLM. Evidence-Based Laboratory Medicine Resources.