Abstract

Background and Objective: Treatment and triage decisions during influenza remain difficult due to lack of reliable severity of illness predictive score. Influenza A/H1N1 induces the expression and release of tissue-factor bearing microparticles (MP-TF), contributing to a prothrombic milieu. However, there are no studies reporting levels of circulating TF-expressing MPs during the course of human influenza. We sought to determine if MP-TF are an early predictor of mortality in critically ill patients with influenza A/H1N1.

Methods: This was a prospective, multicenter, case-cohort pilot study of three academic intensive care units. We prospectively studied 15 patients with primary influenza A/H1N1 that included 7 survivors and 8 non-survivors. For comparison, 27 healthy, medication-free, age- and gender-matched control subjects were also prospectively studied. Plasma was prepared from blood drawn upon ICU admission in influenza patients. MP-TF activity, thrombin-antithrombin complexes (TATc), and D-dimers were measured as markers of activation of coagulation. Plasma cytokine levels were measured on the same blood samples. Patients were followed for the primary outcome of 28-day mortality.

Results: The average admission APACHE II score of the influenza patients was 25.5±9.3, 60% of patients had shock, and the 28-day mortality rate was 53.3% (n=8/15). Compared to healthy controls, influenza patients had significantly higher plasma fibrinogen, C-reactive protein (CRP) MP-TF activity, TATc, D-dimer and a prolonged prothrombin time. However, of these procoagulant markers, only MP-TF activity predicted influenza related mortality (5.6±1.2 pg/ml in non-survivors vs. 1.8±0.8 pg/mL in survivors, p < 0.05; Table 1 and Fig. 1A). MP-TF activity, TATc levels, and D-dimer did not correlate with APACHE II score, platelet count, fibrinogen levels, CRP, or age or between patients with severe sepsis versus septic shock. Influenza non-survivors also had significantly higher plasma IL-8 levels compared with survivors (71.8±29.1 pg/ml vs. 17.3±3.7 pg/mL, p < 0.05; Figure 1B). MP-TF activity and IL-8 levels were significantly and positively correlated (r2 = 0.60, P =0.003; Figure 1C). Other cytokines, TATc, and D-dimer were not different between non-survivors and survivors.

Conclusions: This study demonstrates that plasma IL-8 and MP-TF activity measured upon admission in patients with severe, primary influenza A/H1N1 infection is associated with subsequent mortality. Thus, these biomarkers may serve as very early prognostic markers for patients with influenza A/H1N1.

Table 1.

Characteristics of the influenza patients. Laboratory values, coagulation markers, and plasma cytokines were measured within 24 hours of ICU admission.

 All Influenza A/H1N1 Patients
(n=15) 
Influenza Non-Survivors
(n=8) 
Influenza Survivors
(n=7) 
P value 
Admission Characteristic     
Age, years 43.3±11.0 45.8±4.6 40.4±15.5 0.37 
Male Gender, n (%) 7 (47%) 3 (38%) 4 (57%) 0.45 
Weight, kg 95.5±25.2 86.6±20.9 105.7±27.4 0.15 
BMI, kg/m2 33.3±7.2 31.5±5.0 35.4±9.1 0.31 
Obesity (BMI³30 kg/m210 (67%) 5 (63%) 5 (71%) 0.71 
Tobacco Use, n (%) 4 (27%) 3 (38%) 1 (14%) 0.31 
APACHE II Score 25.5±9.3 27.9±9.1 22.9±9.4 0.31 
Mechanically Ventilated, n (%) 15 (100%) 8 (100%) 7 (100%) -- 
Shock, n (%) 9 (60%) 6 (75%) 3 (43%) 0.21 
P/F Ratio 83±28 84±34 82±22 0.89 
Clinical Outcomes     
ICU Length of Stay, days 21.9±7.7 23.0±7.9 20.7±7.8 0.58 
Duration of Ventilation, days 8.2±1.0 8.5±0.9 7.6±0.9 0.11 
Secondary Bacterial Infection, n (%) 5 (33%) 4 (50%) 1 (14%) 0.28 
Overt DIC, n (%) 15 (100%) 8 (100%) 7 (100%) -- 
Laboratory Values     
Platelets, 103/µL 213±138 154±104 280±150 0.08 
White Blood Cells, K/µL 7.3±4.4 8.5±4.9 5.9±3.5 0.28 
Hemoglobin, g/dL 11.7±1.9 11.5±2.0 12.0±1.8 0.66 
Serum Creatinine, mg/dL 1.1±0.7 1.14±0.74 1.07±0.59 0.84 
Coagulation Markers     
Fibrinogen, mg/dL 571±240 461±253 700±157 0.07 
C-reactive Protein, mg/L 11.0±7.6 11.8±7.4 10.2±8.2 0.70 
PT, sec 20±7.0 19.2±4.7 20.9±9.3 0.67 
aPTT, sec 53.0±22.9 55.1±29.0 50.7±15.0 0.72 
MP-TF, pg/mL 3.8±0.9 5.6±1.2 1.8±0.8 < 0.05 
TATc, ng/mL 11.8±2.7 14.3±3.5 9.1±4.1 0.35 
D-dimer, ng/mL 2439±86 2568±98 2292±134 0.11 
 All Influenza A/H1N1 Patients
(n=15) 
Influenza Non-Survivors
(n=8) 
Influenza Survivors
(n=7) 
P value 
Admission Characteristic     
Age, years 43.3±11.0 45.8±4.6 40.4±15.5 0.37 
Male Gender, n (%) 7 (47%) 3 (38%) 4 (57%) 0.45 
Weight, kg 95.5±25.2 86.6±20.9 105.7±27.4 0.15 
BMI, kg/m2 33.3±7.2 31.5±5.0 35.4±9.1 0.31 
Obesity (BMI³30 kg/m210 (67%) 5 (63%) 5 (71%) 0.71 
Tobacco Use, n (%) 4 (27%) 3 (38%) 1 (14%) 0.31 
APACHE II Score 25.5±9.3 27.9±9.1 22.9±9.4 0.31 
Mechanically Ventilated, n (%) 15 (100%) 8 (100%) 7 (100%) -- 
Shock, n (%) 9 (60%) 6 (75%) 3 (43%) 0.21 
P/F Ratio 83±28 84±34 82±22 0.89 
Clinical Outcomes     
ICU Length of Stay, days 21.9±7.7 23.0±7.9 20.7±7.8 0.58 
Duration of Ventilation, days 8.2±1.0 8.5±0.9 7.6±0.9 0.11 
Secondary Bacterial Infection, n (%) 5 (33%) 4 (50%) 1 (14%) 0.28 
Overt DIC, n (%) 15 (100%) 8 (100%) 7 (100%) -- 
Laboratory Values     
Platelets, 103/µL 213±138 154±104 280±150 0.08 
White Blood Cells, K/µL 7.3±4.4 8.5±4.9 5.9±3.5 0.28 
Hemoglobin, g/dL 11.7±1.9 11.5±2.0 12.0±1.8 0.66 
Serum Creatinine, mg/dL 1.1±0.7 1.14±0.74 1.07±0.59 0.84 
Coagulation Markers     
Fibrinogen, mg/dL 571±240 461±253 700±157 0.07 
C-reactive Protein, mg/L 11.0±7.6 11.8±7.4 10.2±8.2 0.70 
PT, sec 20±7.0 19.2±4.7 20.9±9.3 0.67 
aPTT, sec 53.0±22.9 55.1±29.0 50.7±15.0 0.72 
MP-TF, pg/mL 3.8±0.9 5.6±1.2 1.8±0.8 < 0.05 
TATc, ng/mL 11.8±2.7 14.3±3.5 9.1±4.1 0.35 
D-dimer, ng/mL 2439±86 2568±98 2292±134 0.11 

Figure 1.

MP-TF activity and IL-8 predict mortality in patients with influenza A/H1N1.

(A) Plasma levels of MP-TF activity and (B) IL-8 levels in survivors and non-survivors. (C) Correlation between MP TF activity and IL-8 levelsin H1N1 influenza-infected patients (*P <0.05).

Figure 1.

MP-TF activity and IL-8 predict mortality in patients with influenza A/H1N1.

(A) Plasma levels of MP-TF activity and (B) IL-8 levels in survivors and non-survivors. (C) Correlation between MP TF activity and IL-8 levelsin H1N1 influenza-infected patients (*P <0.05).

Disclosures

No relevant conflicts of interest to declare.

Author notes

*

Asterisk with author names denotes non-ASH members.