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Year : 2019  |  Volume : 62  |  Issue : 4  |  Page : 578-581
Role of procalcitonin, Il-6 and C- reactive protein in suspected cases of sepsis

Department of Microbiology, PGIMER, Dr. RML Hospital, New Delhi, India

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Date of Web Publication14-Oct-2019


Objectives: To study the role of serum procalcitonin as a diagnostic biomarker in sepsis and to compare it with other sepsis markers (IL-6, CRP) in patients of suspected sepsis. Materials and Methods: A total of 80 patients were included in this study from ICU and each patient was investigated for serum Procalcitonin, Interleukin-6 and C-reactive protein levels by ELISA along with blood cultures by BacT/Alert system. Result: Procalcitonin along with CRP is a better diagnostic tool for sepsis.

Keywords: Blood culture, CRP, IL-6, procalcitonin, sepsis

How to cite this article:
Sharma S, Duggal N. Role of procalcitonin, Il-6 and C- reactive protein in suspected cases of sepsis. Indian J Pathol Microbiol 2019;62:578-81

How to cite this URL:
Sharma S, Duggal N. Role of procalcitonin, Il-6 and C- reactive protein in suspected cases of sepsis. Indian J Pathol Microbiol [serial online] 2019 [cited 2023 Jun 7];62:578-81. Available from:

   Introduction Top

Sepsis is a life-threatening infection, affecting approximately 27 million people worldwide each year. Without appropriate treatment, sepsis can progress to severe sepsis (sepsis with organ dysfunction) and septic shock, which causes some 8 million deaths per year.[1] A recent study in India reported that 28.3% of patients contact sepsis during their ICU stay and have 34% mortality rate.[2]

Sepsis is characterized by non-specific symptoms and clinical diagnosis remains difficult. Even when microbiologic diagnostics is available, bacteremia is only identified in a proportion of patients. Early institution of an appropriate antimicrobial regimen is associated with a better outcome.[3] Delays in empirical treatment for sepsis increases mortality and cost, making timely recognition of infection and initiation of appropriate therapy an important goal.[4] Due to the involvement of multiple organs in sepsis, the inflammatory response expand the number of potential biomarker testing for its diagnosis. An ideal biomarker for bacterial infections should facilitate early rapid diagnosis, predict the course and prognosis of the disease and guide therapeutic decisions (e.g., antibiotic stewardship).[5]

Irrespective of numerous studies, a single ideal biomarker has not yet been identified; thus an alternative approach is to shift research focus to determine the diagnostic relevance of multiple biomarkers when used inconcert. Our study was designed with the objective of evaluating the efficacy of PCT as a diagnostic marker of sepsis and compared with other markers, such as CRP and IL-6 and relate these biomarkers with blood culture positivity, in a tertiary care hospital as ours.

   Materials and Methods Top

Our study comprised of 80 patients >18 years of age, either sex, admitted in medical ICU fulfilling the American College Of Chest Physician's Criterion (ACCP) for the diagnosis of sepsis (≥2 of the following) (a) Temperature >38°C/<36°C, (b) Heart rate >90 bpm, (c) Respiratory rate >20 breaths/min or paCO2 <32 mm Hg and (d) WBC count >12,000 cells/mm 3 or <4000 cells/mm 3 or >10% immature (band) forms.

Patients admitted with history of trauma, surgical procedures and diagnosed with medullary carcinoma of thyroid were excluded. Samples were collected after informed consent at inclusion. For PCT, IL-6 and CRP 2-3 ml of blood was collected aseptically. It was clotted, centrifuged and serum was separated and further stored at 2-8°C for up to 3 days or frozen at −20°C for longer period. Testing for these inflammatory markers was done by commercially available ELISA (enzyme linked immunosorbent assay) kits. Blood cultures were done by the automated BacT/Alert BioMerieux system. A paired blood sample (10-20 ml each) was collected in BacT/Alert bottles from two non-continuous veins with strict aseptic precautions.[6]

Statistical analysis

Categorical variables were presented in number and percentage and continuous variables were presented as mean ± SD and median. Normality of data was tested by Kolmogorov-Smirnov test. (Rejected normality, non-parametric test was used). Quantitative variables were compared using Unpaired t-test/Mann-Whitney Test (when the data sets were not normally distributed) between the two groups and Anova/Kruskal wallis test (for non-parametric data) between more than two groups. Qualitative variables were correlated by Chi-square test. A P value <0.05 was considered statistically significant. The data was entered in MS EXCEL spreadsheet and analysis was done using Statistical Package for Social Sciences (SPSS) version 21.0.

   Results Top

Procalcitonin levels

To study the values of PCT obtained, they were divided into four groups based on the severity of sepsis, thus helping in diagnosing sepsis patients. Similar PCT grouping have also been used in other studies.[7],[8]

  1. PCT >10 ng/ml: Severe bacterial sepsis or septic shock
  2. PCT 2-10 ng/ml: Severe systemic inflammatory response, most likely due to sepsis
  3. PCT 0.5-1.9 ng/ml: SIRS; A systemic infection cannot be excluded
  4. PCT <0.5 ng/ml: Local bacterial infection possible; sepsis unlikely.

Out of 80 patients, procalcitonin was positive in 67 patients. The minimum value of procalcitonin which was obtained was 0.18 ng/ml and maximum was 40.64 ng/ml, mean being 16.08 ng/ml; 7 patients had PCT <0.5 ng/ml with a median value of 0.28 ng/ml; 6 patients had PCT between 0.5 and 1.9 ng/ml with a median of 1.63 ng/ml; 10 patients were in 2-10 ng/ml group with median of 6.99 ng/ml and 57 patients had PCT >10 ng/ml with median value of 20.77 ng/ml [Table 1].
Table 1: Distribution of procalcitonin levels

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Distribution of IL-6 and CRP as per the PCT levels: To study the correlation of PCT with IL-6 and CRP, the IL-6 and CRP levels were distributed into the four PCT groups. The minimum value of IL-6 obtained was 4.4 pg/ml and maximum was 280.28 pg/ml. The mean ± SD values of IL-6 in 10 patients with sepsis was 27.59 ± 14.3 and in 57 patients with severe sepsis, median value of IL-6 was 94.82 ± 78.21. The minimum value of CRP obtained was 10 mg/l and maximum value was 220 mg/l. The mean ± SD of CRP in 10 patients with sepsis was 73.5 ± 24.73 and in 57 patients with septic shock was 124.3 ± 39.67 [Table 2].
Table 2: Distribution of IL-6 and CRP levels as per the PCT values

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Blood culture

Out of 80 patients, 37 (46.25%) blood samples were culture positive and 43 (53.75%) were culture negative. In 37 culture positive cases, the most common organisms obtained were Gram negative bacilli 18 (48.64%), maximum being Klebsiella spp. 8 (44%), followed by Pseudomonas spp. 5 (28%) and Acinetobacter spp. 5 (28%). Gram positive cocci were 13 (35.13%) of the total culture positive cases including Staphylococcus aureus 5 (38%).

Correlation of blood culture with three biomarkers [Table 3]
Table 3: Correlation of culture positive cases with the three biomarkers

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In patients who had local infection and SIRS, none had positive blood cultures. Out 10 patients who had sepsis, 3 (30%) had positive cultures (PCT mean value 5.42 ng/ml) and out 57 patients with septic shock, 34 (59.65%) had positive culture (PCT mean value 22.2 ng/ml). The mean values of IL-6 in 3 culture positive cases in sepsis group was 16.5 pg/ml and in 34 culture positive patients in severe sepsis group was 86.96 pg/ml. Similarly, the mean value of CRP in the two groups was 63.33 and 128.53 mg/L, respectively.

   Discussion Top

Out of 80 patients, 7 patients had PCT <0.5 ng/ml with a median value of 0.28 ng/ml; 6 patients had PCT between 0.5 and 2 ng/ml with a median of 1.63 ng/ml; 10 patients were in 2-10 ng/ml group with median of 6.99 ng/ml and 57 patients had PCT >10 ng/ml with median value of 20.77 ng/ml.

These results were similar to the results obtained from studies by Harbarth et al. and Viallon et al. In the study by Harbarth et al. median PCT levels were 0.6 ng/ml for SIRS; 3.5 ng/ml for sepsis, 6.2 ng/ml for severe sepsis; and 21.3 ng/ml for septic shock.[9],[10] In another study, the median PCT serum levels were 3.2, 13.8, and 26.5 ng/ml in patients with sepsis, severe sepsis, and septic shock, respectively. In our study, 67 out of 80 patients could be diagnosed as sepsis on basis of the PCT values. The range of PCT obtained in patients with sepsis was 4.15-8 ng/ml and in septic shock was 10.65-40.64 ng/ml. These ranges can help in diagnosing a patient with sepsis if the patient is tested for PCT and the value falls in between the range. Similarly, the range of PCT obtained in our study for SIRS was 1.2-1.9 ng/ml, which can help in early diagnosis of sepsis by testing for PCT and monitoring the range in a patient with suspected sepsis. This signifies that PCT can be used as a tool for diagnosis of sepsis.

IL-6 levels in patients with sepsis and in septic shock were observed to be significantly increased. The mean value ± SD of IL-6 in sepsis was 27.59 ± 14.3 pg/ml and in septic shock was 94.82 ± 78.21 pg/ml supporting the high PCT values in these groups thus helping in the diagnosis of sepsis and septic shock. IL-6 levels were not significantly increased in patients with local bacterial infection and in patients with SIRS. Thus, no role of IL-6 was seen in diagnosis of SIRS.

The minimum value of CRP obtained was 10 mg/l and maximum value was 220 mg/l, mean being 103.4 mg/l. The median value of CRP in six patients with SIRS was 45 mg/l, whereas in 10 patients with sepsis was 80 mg/l and in 57 patients with septic shock was 120 mg/l. The values of CRP were observed to be raised in all three groups. This signifies that high levels of CRP supported the high PCT values, thus helping in the diagnosis of SIRS, sepsis and septic shock. Our results were similar to results of other studies.[3],[11]

Considering blood culture as the gold standard, the sensitivity of PCT was 83.78% and specificity was 72.09% (P < 0.0001). On the other hand, the sensitivity and specificity of CRP (cut-off >80 mg/l, P value 0.001) and IL-6 (cut off 20.22 pg/ml, P value 0.055) were 78.38%, 48.84%, 78.38% and 46.51%, respectively. Using ROC analysis, PCT best predicted septicemia, followed by CRP (0.78 vs. IL-6 0.62 and CRP 0.69). Similar findings were observed by other studies stating PCT as the best predictor of sepsis when compared with IL-6 and CRP with 73% sensitivity and 70% specificity with a cut-off of 0.5 ng/ml.[12] A meta-analysis evaluated 30 studies with 3244 patients yielded a sensitivity of 77% and specificity of 79% indicating PCT as a useful biomarker for diagnosis of early sepsis.[13] In one study,[11] the cut-off for the diagnosis of sepsis was 50 mg/l (sensitivity 98.5% and specificity 75%) and in another study,[14] the cut-off value was 79 mg/l (sensitivity 71.8%, specificity 66.6%). However, the most discriminatory CRP level has not yet been found and it may be different in diverse infections in patients with suspected sepsis. Published data point to a CRP value between 50 and 100 mg/l for diagnosing sepsis, but CRP response is considered as non-specific and should never be used as a single diagnostic tool. A study stated that PCT but not CRP, was a good predictor of infection in intensive care patients with suspected sepsis.[15] Another study found PCT to be useful and better than CRP in predicting infections and multiorgan dysfunction syndrome in patients with suspected sepsis.[16] On the other hand, studies have suggested that the diagnostic accuracy of IL-6 is limited in critically ill patients which is due to the nonspecific elevation caused by the accompanying inflammation, independent of the infection. In contrast to IL-6, PCT does respond rather to an infection than to the inflammation.[17] Moreover, blood cytokine concentrations are rather erratic and their time course is not clearly in concert with the course of sepsis, making interpretation difficult.[18],[19]

Correlation with blood cultures

In patients who had local infection and SIRS, none had positive blood cultures [Table 3]. Out of 10 patients who sepsis, 3 (30%) had positive cultures (mean value 5.42 ng/ml) whereas out of 57 Patients who had severe sepsis, 34 (59.65%) had positive cultures (mean value 22.2 ng/ml). It was observed that more culture positive cases were seen in severe sepsis, that is, septic shock than in sepsis and higher PCT levels were observed in culture positive cases (P value <0.05). The IL-6 and CRP levels were observed to be correlated with the high PCT levels in blood culture positive cases (P value <0.05). Our findings were similar to other studies.[20],[21] Studies have stated that culture-positive sepsis is associated with severity of sepsis, longer hospitalizations, and higher mortality. Another study by Nakamura et al. observed that elevated procalcitonin levels were correlated with positive blood culture findings, confirming its diagnostic value in general ICU settings. Another study showed that CRP and IL-6 were correlated with the levels of PCT in positive blood culture sepsis, improving their diagnostic probability. Blood culture reflects the current gold standard for the detection of bloodstream infection, since viable microorganisms isolated from the blood can be analysed to identify species and susceptibility to antimicrobial therapy.[22] The practical value of culture in the diagnosis of sepsis, however, is impaired by the delay in the time to results and the fact that positive blood cultures can be found for only approximately 30% of these patients.[23] Furthermore, it is known that the sensitivity for many slow-growing and fastidious organisms is low.[24] Another study stated that if all microbiological cultures are negative and a clear source of infection has not declared itself by 24 hour, a repeat low PCT, combined with clinical judgement, provides a strong argument for discontinuing antimicrobial therapy and searching for an alternative diagnosis. Such an approach is likely to avoid ≥3–4 days of broad-spectrum antibiotic therapy per patient. Studies have proposed sequential measurement of PCT in identifying healthcare-associated infection with some evidence that PCT measured twice or thrice weekly and on the day infection is suspected for the first time might be sufficient and clinically useful.[25] However, testing of PCT is expensive and although this approach is attractive, it is yet to be subjected to robust cost-effectiveness analyses especially in Indian settings.

   Conclusion Top

In a tertiary care hospital such as ours, our study has helped us to diagnose cases of sepsis on basis of PCT, CRP and blood cultures. Among the biomarkers tested (PCT, IL-6 and CRP), PCT was found to be a valuable and reliable marker for early diagnosis of sepsis especially in critical care patients where early recognition and prompt treatment can reduce morbidity and mortality. Thus, PCT in combination with CRP and blood cultures is a good diagnostic tool for sepsis.

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Conflicts of interest

There are no conflicts of interest.

   References Top

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Correspondence Address:
Shiwangi Sharma
Department of Microbiology, PGIMER, Dr. RML Hospital, New Delhi - 110 001
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/IJPM.IJPM_762_18

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