Quantifying the stress induced by distress in patients with lumbar disc herniation in terms of natural killer cell activity measurements: chromium release assay versus multiparameter flow cytometric assay

STUDY DESIGN: A comparative study was conducted. OBJECTIVES: To attempt quantification of the stress in patients with lumbar disc herniation by measuring natural killer cell activity, and to evaluate the assay methodology. SUMMARY OF BACKGROUND DATA: Stressful events may have adverse effects on health. Distress in the patient with lumbar disc herniation also may be a stressful event. Previous findings have shown the activity of natural killer cells to be impaired in medical student volunteers and after bereavement or other stressful life events. However, the stress in patients with spinal disorders has not been evaluated. The standard assay for natural killer cell activity has been the chromium release assay. However, this assay requires the use of radioactive chromium. Flow cytometric assay is a nonradioactive method that analyzes the activated natural killer lymphocyte subsets: CD45+, CD56+, CD69+. METHODS: Peripheral blood lymphocytes were obtained from 20 patients with lumbar disc herniation (mean age, 30.8 years) and 20 healthy individuals (mean age, 38.9 years). Both chromium release assay and flow cytometric assay were performed for each patient. RESULTS: The mean natural killer cell activity in the patients (8.0% +/- 4.3%) was significantly lower than in the 20 healthy adult volunteers (12.6% +/- 4.5%). The mean natural killer cell activity in the healthy volunteers was 12.6% +/- 4.5% for the chromium release assay and 11.0% +/- 4.1% for the flow cytometric assay. The correlation (r = 0.77) of natural killer cell activity between the two methods was high. CONCLUSIONS: Natural killer cell activity in the patients with lumbar disc herniation was significantly lower than in healthy individuals, and the stress induced by pain and other distress may be present in patients with lumbar disc herniation. For measuring natural killer cell activity, flow cytometric assay is a reproducible assay, and it may be a viable alternative to the standard chromium release assay.