Does the timing of prednisone (corticosteroid) intake affect Natural Killer (NK) cell test results?

Effect of Prednisone on NK Cell Testing

Taking prednisone before an NK cell test can significantly alter the results, as corticosteroids directly suppress NK cell activity and cytotoxicity, making the test results unreliable. 1

Impact of Prednisone on NK Cell Function

Prednisone and other corticosteroids have been shown to have significant effects on Natural Killer (NK) cell function:

• Direct suppression: Methylprednisolone (which prednisone converts to in the body) significantly inhibits NK cell proliferation, cytotoxicity, and anti-viral effects 1
• Timing matters: The FDA label for prednisone indicates that its effects on the body follow a diurnal pattern, with maximal adrenal cortex activity between 2 am and 8 am 2
• Suppressive mechanism: Corticosteroids inhibit NK cell activity by:
  • Reducing NK cell adhesion to target cells 3
  • Inhibiting expression of NK cell activation markers 1
  • Decreasing production of interferon-γ 1

Comparison of Test Results

In the patient's case:

• First test: Prednisone taken at 9 am, test at 10 am (1 hour after medication)
• Second test: No prednisone taken, test at 10 am

The second test without prednisone will provide more accurate results of the patient's true NK cell function. Research shows that prednisone can suppress NK cell cytotoxicity by approximately 18.5% 1, which would significantly impact the first test results.

Clinical Implications

For accurate NK cell testing:

• Timing recommendation: Ideally, prednisone should be held before NK cell testing
• Duration of effect: If prednisone cannot be held, it's important to note that its suppressive effects on immune function can last for 1-1.5 days following a single dose 2
• High-dose considerations: For patients taking ≥20 mg daily of prednisone, the immunosuppressive effects are even more pronounced 4

Guidance for Future Testing

• Optimal timing: Schedule NK cell testing before daily prednisone dose when possible
• Consistency: For serial monitoring, always perform tests under the same conditions (either always before or always after prednisone) to ensure comparable results
• Documentation: Always note prednisone timing and dosage when interpreting NK cell test results

Common Pitfalls

• Failing to account for medication effects when interpreting NK cell results
• Inconsistent timing of prednisone administration relative to testing
• Not considering that different corticosteroids have varying durations of immunosuppressive effects
• Overlooking that the return to normal NK cell function may take several days after stopping corticosteroids 5

For this patient, the second test (without prednisone) will likely provide a more accurate assessment of her baseline NK cell function, as it avoids the direct suppressive effects of prednisone on NK cell activity.