Evaluation of natural killer cell assay performance on shipped blood specimens.
Querec, Troy D, Abrams, Joseph, Stewart, Jennifer J et al. · Journal of immunological methods · 2021 · DOI
Quick Summary
This study tested different laboratory methods for measuring natural killer (NK) cell function—an immune system measurement that may be important for ME/CFS—using blood samples that were shipped overnight instead of tested immediately. Researchers compared three different testing approaches and found that two of them (CRCA and FCCA) gave similar results when blood samples were processed a day after collection, suggesting these tests could work for clinical settings where samples need to be shipped.
Why It Matters
NK cell dysfunction is a potential biomarker for ME/CFS, but research has been limited by the need to test samples immediately after collection. This study demonstrates that practical shipping and overnight storage protocols can maintain the validity of NK cell testing, which could enable standardized multi-site clinical trials and broader diagnostic implementation for ME/CFS patients.
Observed Findings
Same-day CRCA testing on whole blood showed median NK cytotoxicity of 10.0% (IQR 7.2%), serving as the reference standard.
Next-day FCCA on isolated PBMCs correlated strongly with same-day CRCA on PBMCs (R²=0.8, p=0.001).
Next-day CRCA testing was compromised in both whole blood and frozen PBMC specimens, making these conditions unsuitable.
CD107a surface expression did not correlate with direct cytotoxicity measures (CRCA and FCCA).
PBMCs isolated after overnight ambient temperature shipping and storage maintained sufficient viability for reliable NK function measurement.
Inferred Conclusions
NK cell cytotoxicity can be standardized and measured reliably in PBMCs after overnight shipping at ambient temperature using CRCA or FCCA assays.
FCCA offers a practical alternative to CRCA for shipped specimens, showing strong concordance and requiring less specialized equipment.
CD107a expression is not an adequate surrogate marker for direct NK cytotoxicity measurement in this context.
Remaining Questions
Does this assay standardization translate into clinically useful diagnostic accuracy for identifying NK dysfunction in ME/CFS patients?
How do these shipping-tolerant assays perform in larger, geographically diverse patient populations and clinical settings?
What This Study Does Not Prove
This study does not establish that NK cell dysfunction causes ME/CFS or prove its diagnostic utility; it only addresses technical feasibility of measuring NK function under shipping conditions. The small sample size (31 participants) and limited generalizability (only three clinics) mean results may not apply across all laboratory settings. Correlation between assays does not confirm their clinical relevance for ME/CFS diagnosis or prognosis.