As per the Third International Consensus , sepsis is defined as “ Life-threatening organ dysfunction caused by a dysregulated host response to infection”[3]. Millions of people are affected every year due to sepsis and nearly one in three to one in six have associated mortality due to sepsis[5]. Sepsis outcomes can be improved by quick identification and proper management in the initial hours.
The primary pathophysiology of sepsis is the host's response to infection. Due the dysregulated host responsiveness, there is organ dysfunction. The underlying biochemical, pathological and physiological derangements due to sepsis are responsible for this.
Biomarkers have played a very important role in sepsis management over the years. As the years pass on, there are newer and novel biomarkers, which have greatly influenced the outcome of patient care. Pierrakos et al performed an analysis in 2019 using 5327 studies, evaluating 258 different biomarkers in sepsis [4]
Identifying the cytokines in the human body is difficult as they rapidly disappear from the circulation after their release. Also more often, the cytokines act locally. An indirect way to measure the immune reactions is to capture the biochemical changes induced by the cytokines. On such biochemical marker, which can help to analyse the state of cell mediated activation is Serum Neopterin.
Neopterin was initially detected in larva of bees in 1963. H. Rembold named it as “Novapterin”. Novum means new in Latin , Apis is derived from honey bee in Latin and pterin as it is pterin structure. Finally, the substance was given the name "Neopterin" to indicate that it may herald a new era in pteridine study (Neo means new in Greek).[6]
Interferons are produced by T-lymphocytes and activated macrophages and monocytes. Guanosine triphosphate is broken down by the macrophage enzyme GTP-cyclohydrolase (GTP-CH1) to produce 7,8-dihydroneopterin-triphosphate. After being hydrolysed by phosphatases, the aforementioned molecule is released as neopterin
Half-life of neopterin is 90 minutes and renal excretion may have modification on it.[7]
The enzyme-linked immunosorbent assays are the most recent measurement methods (ELISA).Neopterin is biochemically inert and excreted by the kidneys. Measurement of Neopterin rather than reflecting a single cytokine, is representation of cellular response. Neopterin can be measured in the serum or the urine. Normal serum Neopterin values is less than 10 nmol/L . Neopterin is an excellent diagnostic marker for viral infections[8]. Neopterin is a very good marker in predicting the clinical course in HIV patients [9]. Serum Neopterin levels also demonstrated a strong clinical relation in patients with pulmonary tuberculosis. Neopterin levels increased as the condition deteriorated.
It has very good predictive value in malignancies. Ozger et al did the study on COVID-19 patients and showed that Serum neopterin can be used as prognostic biomarker for COVID-19 infections.[10]
Neopterin also has a very important role in graft rejections. As it is a T cell stimulation mediated product, the levels are elevated in transplant rejection[11]
In our study, serum neopterin levels were studied across 3 groups , sepsis with MODS , sepsis without MODS and non-sepsis. There was significant elevation(p<0.001) in neopterin levels in patients with sepsis, 87.00(40.00, 129.00) as compared to non-sepsis group 22.00(12.00, 39.00). Hence Serum Neopterin is good marker in identifying sepsis. Moreover, there was significant elevation (p=0.001) in levels of group 1, 123.00 (79.25, 146.00) as compared to group 2 54.00(34.00, 88.50). Hence, serum neopterin could differentiate MODS in patients with sepsis.
The serum neopterin levels were checked dynamically at 0, 48 hours. The neopterin levels were higher in group 1 compared to the other groups across both the timelines. There was significant downtrend (p=0.002) in group 1 and p = 0.004 in group 2 and p= 0.501 in group 3 respectively. Hence neopterin can used as a marker to determine progression of sepsis.
The correlation of serum neopterin with different scores like SOFA, Qsofa and APACHE were studied. At 48 hours, serum neopterin had strong relation with Sofa (0.798), APACHE (0.789) and Qsofa (0.611). This shows the serum neopterin is good predictor of the clinical status of the patients. Sequential Organ Failure Assessment (SOFA) score is used to determine the level of organ dysfunction. Serum Neopterin levels had a strong correlation with SOFA scores at 0 hours, 48 hours, and 96 hours, hence serum neopterin is an effective marker in predicting organ failure. Girgin et al showed that serum neopterin had a positive correlation with APACHE scores in ICU patients[12], However, no previous tests for association with other markers were done.
The area under the curve (AUC) was plotted for different inflammatory marker namely the Serum Neopterin, Serum Procalcitonin, CRP, ESR and total counts to diagnose sepsis. The AUC was maximum with CRP (1.000, p<0.001) followed by Serum Neopterin (AUC= 0.979, P <0.001). Serum Neopterin had a sensitivity of 92.31 % and specificity of 100 % and accuracy of 94.55% in predicting sepsis. Hence Neopterin is a good marker in predicting sepsis.
Of the 5 markers compared, only neopterin and procalcitonin were good markers to diagnose MODS in patients with sepsis. The AUC for serum neopterin was 0.834(p<0.001) and AUC for procalcitonin was 0.714(p=0.023). The sensitivity was 92.31 % and specificity was 100 % and accuracy was 94.55 % for serum neopterin to predict MODS. In comparison, the sensitivity of procalcitonin was 59%, specificity was 76% and accuracy was 66 %. Hence serum neopterin is a better marker in diagnosing MODS in patients with sepsis than procalcitonin.
Based on the data obtained, cut offs were calculated for the different markers. To diagnose sepsis, the cut-off calculated for serum neopterin was >43 and the p value was <0.001. However, the normal neopterin levels are less than 10. Our study has a different cut off and hence further larger volume studies need to done to validate the obtained cut-off. To diagnose MODS, the cut off value for serum neopterin was > 122 and the p value obtained was <0.001. Hence in our study, we have obtained a new cut off value for diagnosing sepsis and also, we have a cut-off for diagnosing MODS.
Zhang et al in his study showed that neopterin can help in differentiating MODS from sepsis. Along with above, we have calculated cut off for neopterin and also other markers and we have also compared the efficacy of different markers in sepsis and also in sepsis with MODS, which is novel in our study[13] and also the correlation of serum neopterin with the different sepsis scores was also calculated in our study.
Our study has shown that serum neopterin is superior marker compared to others in diagnosing MODS.
The association serum neopterin and length of hospital stay was studied. There was a statistically significant (p=0.047) , mild positive correlation( correlation coefficient r =0.269) between length of hospital stay and serum neopterin levels at 0 hours, hence neopterin may not be a perfect marker in predicting length of hospital stay.
STRENGTHS AND LIMITATIONS
The study was performed across 3 groups of people and the results showed good statistical significance, which has a very good advantage in our study. The comparisions between neopterin and other markers had a good significance.
However, the main limitation of the study , was it was performed in a single centre, with 55 subjects. Larger volume studies, need to be performed to validate the results.