Inter-Laboratory Variability

Inter-laboratory variability refers to differences in test results when the same sample, or similar samples, are analyzed by different laboratories. In asbestos science, it describes how fiber counts, mineral identifications, and lung tissue burden measurements can vary meaningfully from one lab to another, even when each lab follows accepted methods.

Origin

The concept comes from analytical chemistry and metrology, where round-robin testing programs in the mid-20th century revealed that identical samples often produced different results across labs. It became a recognized issue in asbestos analysis in the 1980s as electron microscopy methods (TEM, SEM) and fiber-counting protocols (NIOSH 7400, ISO 10312) were standardized in response to these discrepancies.

Significance in Asbestos Context

Inter-laboratory variability matters because asbestos cases often turn on quantitative measurements, fiber counts in air samples, asbestos body counts in lung tissue, or trace fiber identifications in talc or insulation. Defendants frequently use variability between labs to challenge a plaintiff's expert findings, arguing that the numbers are unreliable or that another lab would have reported lower exposure. Conversely, when multiple independent labs reach similar conclusions about a sample or a worker's lung burden, that agreement strengthens the scientific case. Understanding this issue helps explain why your legal team may seek confirmatory testing at a second laboratory, why qualifications and accreditation of the testing lab matter, and why expert witnesses spend time discussing methodology rather than just results.

Example Sentence

The defense expert pointed to inter-laboratory variability to argue that the plaintiff's fiber-burden analysis was unreliable, but our expert showed that two separate accredited laboratories had reached nearly identical conclusions about the lung tissue sample.

Related Terms

Fiber Burden Analysis, Transmission Electron Microscopy (TEM), NIOSH 7400, Quality Assurance, Round-Robin Testing, Analytical Sensitivity

Notes

• Ask whether the laboratory analyzing your samples is accredited (for example, by NVLAP, AIHA-LAP, or A2LA) and what proficiency testing programs it participates in.
• If fiber counts or tissue burden results are central to your case, your legal team may arrange split-sample testing at a second independent lab. Preserve any remaining tissue or sample material to allow this.
• Request that pathology blocks, slides, and unused tissue from biopsies or autopsies be retained rather than discarded, since these may be needed for future or confirmatory analysis.
• When reviewing expert reports, look for the specific method used (e.g., TEM with SAED, PLM, SEM-EDS) and the lab's detection limits. These directly affect how results from different labs should be compared.