Comparative study of procalcitonin versus c-reactive protein in the diagnosis of sepsis in children below 16 years-a single centre observational study

Introduction: Given the limitation of non-specific nature of signs, symptoms and physical examination in diagnosing sepsis; especially in young children, a diagnostic marker that will aid in an early diagnosis is needed. Procalcitonin satisfies most of the criteria for smart biomarker of sepsis. The present study is done to compare procalcitonin (PCT) with C-reactive protein (CRP) as a diagnostic marker of sepsis in children. Materials & Methods: A prospective observational study was done in the Department of Paediatrics, ASRAM Medical College and Hospital, Eluru from July 2015 to June 2016. Children admitted to PICU during the above tenure are included in the study. Specific inclusion and exclusion criteria are formulated with a sample size of 100. Procalcitonin level is analyzed by enzyme linked immunoluminometric assay using Elecsys Brahms PCT kit.CRP analysis is done using immunoturbidometry which is a quantitative method. Results: Out of 100 children 72 have sepsis. The mean procalcitonin level in children with sepsis is 19.09 ± 24.53 ng/ml compared to 0.34 ± 0.49 ng/ml in children without sepsis. In comparing sepsis with asepsis, PCT (Cutoff value of 0.58ng/ml) have a better sensitivity (90.3%) and specificity (92.9%) than CRP (Cut off value of 0.7mg/dl) sensitivity of 87.5% and specificity of 57.1%. Conclusion: PCT offers better sensitivity and specificity than CRP, to differentiate sepsis from asepsis. In febrile children PCT is a better diagnostic marker of sepsis than CRP.


Introduction
Fever is the most common reason for visits to paediatrician. Given the limitation of non-specific nature of signs, symptoms and physical examination in diagnosing sepsis; especially in young children, a diagnostic marker that will aid in an early diagnosis is needed. The utility of a biomarker is enhanced if it reflects the severity of infection and progression of the disease as well as the effectiveness of therapy.
Blood culture is the gold standard but requires precious 48 hours and the positivity yield is low. PCT satisfies most of the criteria for smart biomarker of sepsis [1].
Procalcitonin, a polypeptide identical to prohormone of calcitonin is initially described as a potential marker of bacterial disease by Assicot et al [2]. When its elevated levels were reported in patients with bacterial infection, PCT became an important protein in the detection and differential diagnosis of inflammatory states [3].

Cut off Values of Procalcitonin
Plasma PCT has a normal half-life of 25-30 hours and 30-45 hours in patients with severe renal dysfunction. PCT detectable in the plasma during inflammation is not produced by C-cells of the thyroid [3]. The probable sites of PCT production in inflammation are the neuroendocrine cells in the lungs or intestine. The expression of mRNA coding PCT has been demonstrated in vitro in monocytes, stimulated by endotoxin or inflammatory cytokines [4]. PCT is not elevated by viral infections or autoimmune inflammation, or by the presence of neoplasm's [5]. Physiologically PCT can be raised in neonates up to 72 hours. Birth weight and gestation did not significantly affect normal PCT values [6]. Sequential measurements of procalcitonin have shown a rapid fall within 48 hours of antibiotic administration. An immunoluminometric procalcitonin assay is now commercially available (BRAHMS diagnostika) and values can be obtained within two hours of blood sampling.
Volanakis and Kaplan identified the specific ligand for CRP in the pneumococcal C polysaccharide as phosphocholine; part of the techoic acid of pneumococcal cell wall. CRP, an acute phase protein involved in coagulation, acts as opsonin for gram positive bacteria to aid in phagocytosis. CRP is synthesized by the liver in response to and as a part of the inflammatory response. IL-6 is the major stimulus for production of CRP along with IL-1, TNFα [6]. CRP is synthesized within 6-8 hours of exposure to an infective process or tissue damage.
Its half-life is 19 hours and may show a thousand fold rise during an acute phase response. Serial measurements at 24 and 48 hours after the onset of illness considerably improve the sensitivity to 82% and 84% respectively [7]. Sequential measurements of CRP levels are helpful in determining the response to anti-microbial therapy and duration of treatment.
Aims and objectives of the study: To compare Procalcitonin (PCT) versus C-reactive protein (CRP) as a diagnostic marker of sepsis in children and to assess the utility of PCT as an early marker in diagnosis of sepsis.

Materials and Methodology
This is a prospective observational study done in the department of Pediatrics, ASRAM medical college and hospital, a tertiary care centre, Eluru, Andhra Pradesh. The study is conducted from August 2015 to September 2016 over a period of 13months.
Inclusion criteria: Children less than 16years of age admitted to PICU with rectal temperature of≥38°C.
Exclusion criteria: Children treated with antibiotics and those who received vaccination in past 48hrs. Known cases of chronic inflammatory disorder and immunodeficiency are also excluded.
Sample size calculation: Based on the mean and SD of previous studies [8,9] with an α value of 0.05 and power (1-α) of 0.8, a sample size of 100 is found to be adequate. Prospective cases were analyzed and data recorded. All children included in the study had fever. Those with symptoms and signs of sepsis are included in sepsis group and rest of the children with no signs and symptoms are included in asepsis group.
Based on International consensus definitions of paediatric sepsis [10,11] children included in the study are divided into two groups -Asepsis and Sepsis. Children satisfying any of the criteria for definite or probable sepsis are included in the sepsis group and the rest are included in asepsis group. After the Institutes ethical committee clearance and informed consent from the guardians, data collected is entered into a structured proforma.

Cohort of Study Identification, Inclusion & Exclusion
Procalcitonin level analysis is done using enzyme linked immunoluminometric assay by using Elecsys BRAHMS PCT kit.Range:0.02-100 ng/mL. CRP analysis is done using immunoturbidometry, with the minimal detectable concentration being 0.1mg/dl. Blood culture is done by Bactec-9050/Micro scan system. The data is analyzed using windostat version 8.6.

Results
Age distribution: In the present study around half of the study population is between 1-20 months of age and 72% of the subjects are under 5 years of age indicating that the most common age group with fever requiring PICU admission is < 5 years.

Final Sample size =100
Written consent not given -255 Children with Fever -675 Using the student's test for statistics, 95% confidence limits, it is found that there is no significant difference in the mean age distribution among two groups (sepsis and asepsis). (p = 0.564).
Gender distribution: Of the 100 children included in the study 57 are males and 43 females. The mean age in males is 32.5 ± 42.5 months. The mean age in females is 49.9 ± 47.2 months. In the present study significant difference does not exist in gender variation among two groups (p = 0.36) Procalcitonin: According to our lab reference parameters, PCT ≤ 0.5 ng/ml is negative and PCT > 0.5 ng/ml is positive.
Distribution of PCT among sepsis and asepsis: Number of children with sepsis and asepsis are 72 and 28 respectively. Distribution of PCT among sepsis and asepsis.
Among 28 patients with asepsis PCT is positive in 2 children (7%) and negative in 26 children (93%). Among 72 patients with sepsis PCT is positive in 65 children (90.3%) and negative in 7 children (9.7%). ROC curve for PCT is constructed comparing children with asepsis and sepsis. These curves are used to identify cut off values and sensitivity and specificity. In comparing asepsis with sepsis the ROC area under the curve (AUC) for PCT is 0.92, a cut off value of 0.58ng/ml yielded.

Asepsis
ROC curve for CRP is constructed comparing children with asepsis and sepsis. These curves are used to identify cut off values and sensitivity and specificity. In comparing asepsis with sepsis the ROC area under the curve (AUC) for CRP is 0.75, a cut off value of 0.7 mg/dl yielded.

Discussion
Interpretation of the literature dealing with Procalcitonin in children is complicated by the diverse age range and nature of the study population and variation in the choice of the cut off value of Procalcitonin.
Age group: Mean age of presentation in our study among asepsis and sepsis is 35. 8  In a Meta analysis, Liliana Simon et al., [19] evaluated the accuracy of determination of PCT and CRP levels for the diagnosis of bacterial infection. PCT level was more sensitive (88% vs. 75%) and more specific (81% vs. 67%) than CRP level for differentiating bacterial from non-infective causes of inflammation. On the basis of this analysis, the diagnostic accuracy of PCT markers was higher than that of CRP markers among patients hospitalized for suspected bacterial infections. In a study by Fernandez Lopez et al [14] the optimum cut off values suggested for detecting any bacterial infection was 0.53 ng/ml (sensitivity : 65% ; specificity: 94%; PPV : 96% ;NPV : 59% ). For detecting invasive bacterial infections was 0.59 ng/ml (sensitivity: 91.3%; specificity: 75 %; PPV: 69%; NPV: 81%).
A study by Mark Hatherill et al., [18]concluded that in critically ill children the admission procalcitonin concentration of 2ng/ml or more is a better diagnostic marker of infection than C reactive protein or leucocyte count. A study by Deis JN et al., [20] compared PCT with interleukin 6 and CRP, and found that IL-6 performed better than PCT which performed better than CRP.

Conclusion
In febrile children admitted to paediatric intensive care unit the admission Procalcitonin concentration is a better diagnostic marker of sepsis than C -reactive protein. A PCT concentration of 0.58 ng/ml might be useful in differentiating sepsis in infants and children.
Funding: Nil, Conflict of interest: None initiated, Perission from IRB: Yes Bibliography