Abstract: Objective To investigate the relationship between plasma helper T cell 1 (Th1)/helper T cell 2 (Th2) cells, endotoxin (ET), prothrombin activity (PTA) and procalcitonin (PCT) and the severity and outcome of sepsis in children. 
Methods Ninety-six children with sepsis in our hospital were selected, and the severity of sepsis was assessed by the Pediatric Critical Care Score (PCIS) and classified into non-critical group (PCIS score >80, n=39), critical group (PCIS score 71-80, n=32), and very critical group (PCIS score ≤70, n=25). The three groups were compared in terms of general data, plasma Th1/Th2 cells, ET, PTA, and PCT levels at admission, and the relationship between plasma indicators and PCIS scores of children with sepsis was analyzed. The 28 d prognosis of children with sepsis was recorded, and plasma Th1/Th2 cells, ET, PTA, and PCT levels at admission in children with different prognosis were compared, and the relationship between plasma indicators and the prognosis of children with sepsis as well as the value of plasma indicators in predicting the prognosis of children with sepsis was analyzed. 
Results The level of Th1/Th2 cells and PTA in very critical group was lower than that in critical group and non-critical group, and lower in critical group than in non-critical group. The levels of ET and PCT in very critical group were higher than those in critical group and non-critical group, and higher in critical group than in non-critical group, and the difference was statistically significant (P＜0.05). Plasma Th1/Th2 cells and PTA levels were positively correlated with PCIS scores of children with sepsis, and plasma ET and PCT levels were negatively correlated with PCIS scores of children with sepsis (P＜0.05). Plasma Th1/Th2 cells and PTA levels at admission were lower in deceased children than in surviving children, and plasma ET and PCT levels were higher than in surviving children (P＜0.05). Plasma Th1/Th2 cells and PTA levels were positively correlated with the prognosis of children with sepsis, and plasma ET and PCT levels were negatively correlated with the prognosis of children with sepsis (P＜0.05). The area under the curve (AUC) of Th1/Th2 cells, ET, PTA, and PCT in predicting the prognosis of children with sepsis as death was 0.808, 0.836, 0.720, and 0.748, respectively, and the combined prediction had the largest AUC of 0.933. 
Conclusion The levels of plasma Th1/Th2 cells and PTA were closely associated with the severity of sepsis in children, and the levels of plasma ET and PCT were negatively correlated with the severity of the disease and closely correlated with the prognosis of the children. The early combined detection of the levels of each index can assist in clinical prediction of the prognosis of the children. 

Key words: plasma Th1/Th2 cells, endotoxin, prothrombin activity, calcitoninogen, sepsis