Interleukin-6 is the Cytokine Used as a Prognostic Marker in Sepsis
Interleukin-6 (IL-6) is the cytokine that can be used as a prognostic marker in sepsis, with elevated levels strongly correlating with sepsis severity, shock development, and mortality.
Evidence for IL-6 as a Prognostic Marker
IL-6 has demonstrated significant value as a prognostic indicator in sepsis for several reasons:
Elevated IL-6 levels correlate with sepsis severity and shock development, with levels up to 7,500 times normal in severe cases 1
IL-6 shows significant correlation with important clinical parameters including:
- Plasma lactate levels (P < 0.0001)
- Heart rate (P = 0.05)
- Inverse correlation with mean arterial pressure (P = 0.01)
- Inverse correlation with platelet counts (P = 0.0002) 1
IL-6 has demonstrated prognostic significance for mortality:
- Higher levels in septic patients who subsequently died compared to survivors (P = 0.0003)
- Even stronger predictive value in patients with septic shock (P < 0.0001)
- All septic patients with levels <40 U/mL survived, while 89% with levels >7,500 U/mL died 1
Recent research confirms IL-6 as an independent predictor of sepsis diagnosis 2
Comparison with Other Cytokines
While multiple cytokines are involved in sepsis pathophysiology, IL-6 demonstrates superior prognostic value compared to other interleukins:
- IL-1β and TNF-α levels do not correlate with mortality rate as strongly as IL-6 3
- IL-6 is a better predictor of outcome than APACHE II score in severe intra-abdominal sepsis (sensitivity 86.4% vs 72.7%, specificity 78.9% vs 57.9%) 3
Clinical Application of IL-6 Measurement
When measuring IL-6 for prognostic purposes in sepsis:
- Timing is important - measurements should be taken within 24 hours of sepsis onset for best prognostic value 3
- Serial measurements may provide better information than single measurements
- IL-6 can be combined with other markers (BUN, MAP) for improved diagnostic accuracy 2
Limitations and Considerations
Despite its value, there are important caveats when using IL-6 as a prognostic marker:
- IL-6 is not specific to sepsis and can be elevated in other inflammatory conditions
- The World Society of Emergency Surgery (2017) notes that inflammatory biomarkers still require further controlled studies before their measurement can fully guide clinical care 4
- IL-6 should be interpreted as part of a systematic evaluation including clinical examination and other diagnostic techniques
Other Potential Biomarkers
While IL-6 shows the strongest evidence, other biomarkers may also have value:
- Procalcitonin (PCT) rises more quickly at onset of inflammation and is cleared more quickly as inflammation resolves 4
- C-reactive protein (CRP) correlates with inflammatory response and is valuable for monitoring treatment response 4
- A cytokine network including IL-6, IL-8, MCP-1, and IL-10 may provide additional prognostic information in the acute phase of sepsis 5
In conclusion, while several cytokines are involved in sepsis pathophysiology, IL-6 has the strongest evidence supporting its use as a prognostic marker, particularly for predicting mortality in septic patients.