Are immature granulocytes and derivatives early predictors of acute appendicitis and acute complicated appendicitis in adults?

Abstract

Background: 

The aim of this study was to investigate the usability of immature granulocyte count (IGC), immature granulocyte percentage (IG%), and IGC to neutrophil ratio (IGC/N ratio), a new inflammatory marker, in both diagnosing acute appendicitis (AA) and differentiation of simple and complicated appendicitis (SA and CA).

Materials and Methods: 

This study was conducted on 262 adult patients who underwent appendectomy. The patients were histopathologically divided into positive and negative appendectomy groups. The patients in the AA group were also divided into SA and CA subgroups. The demographic and laboratory data of the patients were compared.

Results: 

The mean values of white blood cell count, neutrophil-to-lymphocyte ratio, IGC, IG%, IGC/N, and C-reactive protein (CRP) are the parameters that can be used both to diagnose AA and to differentiate CA from SA. In our study, the ability of IGC to predict AA was found to be greater than that of other parameters. For IGC, the area under the receiver operating characteristic curve (AUC) was 0.784, the sensitivity was 98.3% and the specificity was 80%. CRP and IGC/N ratio had the highest specificity predictive values in differentiating CA from SA. For IGC/N, the AUC was 0.702, the sensitivity was 63.9%, and the specificity was 72.3%.

Conclusion: 

IGC is a reliable inflammatory marker in the diagnosis of AA but immature granulocytes and derivatives (IGC, IG%, and IGC/N) cannot be used for predicting CA because of low sensitivity and specificity.

INTRODUCTION

Acute appendicitis (AA) is the most common cause of acute abdominal pain requiring urgent surgical intervention. The life-long risk of developing AA is 7%.[¹²] The majority of the AA cases are simple appendicitis (SA) without any complication. Acute complicated appendicitis (CA) is a serious problem that delays the healing process of patients and causes prolonged length of hospital stay and increased medical costs.[¹] Increased time from onset of symptoms to surgical treatment is a risk factor for CA. A successful treatment depends on early diagnosis and treatment.[³]

Many studies have been conducted for early diagnosis and treatment of AA and its complications. There are many studies indicating that increased white blood cell count (WBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR) can be used as a biomarker to show CA.[⁴⁵] However, despite the use of these biomarkers, it is not easy to differentiate between SA and CA. Therefore, new and more specific biomarkers are needed.

Immature granulocytes are indicative of increased myeloid cell production and these have been shown to increase in infectious and inflammatory conditions.[⁶] Immature granulocyte count (IGC) and immature granulocyte percentage (IG%) are new biomarkers indicative of inflammation that can be easily and rapidly measured from routine complete blood count.[⁷] Studies have demonstrated the ability of IGC and IG% to predict infectious conditions.[⁶⁷⁸⁹] To the best of our knowledge, there are very few studies on IGC and IG% indicating the diagnosis and presence or absence of CA; however, there is no study on IGC/neutrophil (IG/N) ratio. Therefore, we aimed to investigate the usability of IGC, IG% and IGC/neutrophil ratio (N ratio), new inflammatory markers, both in the diagnosis of AA and in differentiating SA from CA.

METHODS

The study was designed as a single-center, retrospective cohort. The patients were selected among patients admitted to a tertiary emergency department and diagnosed with AA between March and September 2019. Our hospital has a capacity of 2000 beds and approximately 360,000 patients are admitted to the emergency department annually. The study was conducted in accordance with the Declaration of Helsinki and was approved by the local ethics committee of the institute. The study protocol was reviewed and approved by the independent review board of our institution (IRB No. 2019-314 obtained on October 10, 2019), written informed consent was obtained from all the patients, who agreed to participate in the study.

All patients were retrospectively reviewed on the hospital information-record system. Our patient population consisted of patients diagnosed with AA according to the ICD-10 (International Classification of Diseases) coding system in the emergency department. The exclusion criteria of our study were patients under the age of 18 years, pregnant patients and those with any comorbid diseases that may affect inflammation. All patients underwent appendectomy and were categorized into two groups as positive appendectomy (PA) and negative appendectomy (NA) according to their histopathological diagnosis. Subsequently, the patients were categorized into the CA and SA subgroups. Catarrhal and phlegmonous appendicitis were considered as SA, while gangrenous and perforated appendicitis and abscess were considered as CA. The laboratory results including demographic data and complete blood count (CBC) results were recorded.

WBC, neutrophil, IGC, IGC%, and also CRP were recorded in the patients' CBC examined during the application to the emergency department. NLR, PLR, and lymphocyte-to-monocyte ratio (LMR) were calculated by proportioning these parameters. Samples were drawn prior to antibiotic administration and patients did not use of NSAIDs or other anti-inflammatory agent. Blood samples were studied from the peripheral vein in Sysmex XN-1000 (Sysmex Corp., Kobe, Japan) automated hematological analyzer using ethylene diamine tetraacetic acid tube and the flow cytometry method. Normal values were respectively considered as 4–10.5 × 10³ mm³ for WBC, 0–0.6 × 10³ mm³ for IG%, 0–0.09 × 10³ mm³ for IGC and 0–5 mg/dl for CRP.

Statistical analysis

Standard deviation and mean values were calculated for the continuous variables. Each of the independent variables was compared using the Chi-square test and according to suitability, the independent t-test. The descriptive statistical analysis of all variables was carried out using SPSS 18.0. The optimal cutoff value of WBC, CRP, IGC, IG%, and IGC/N parameters as diagnostic biomarkers in AA diagnosis and differential diagnosis of CA/SA was analyzed by receiver operating characteristic (ROC) analysis.

RESULTS

Our study included 262 patients who underwent appendectomy with the diagnosis of AA preoperatively. One hundred and fifty-nine patients were male (60.7%) and the mean age was 34.5 years. According to the pathology results, there were 20 patients (7.6%) in the NA group and 242 patients (92.4%) in the PA group. The rate of NA was statistically significantly higher in females than in males (60% vs. 37.7%, respectively, P = 0.043). The mean WBC, IGC, and CRP values were significantly higher in the PA group than in those with NA (P < 0.001 in each parameter). In addition, the mean NLR, IG% and IGC/N values were significantly higher, while the mean LMR was significantly lower in the PA group than in those with NA. The comparison between the PA and NA groups is shown in Table 1.

Table 1: Comparison between positive and negative appendectomy groups regarding the studied parameter

According to the pathology results of the patients with AA, there were 206 patients (85.1%) in the SA group and 36 patients (14.9%) in the CA group. According to gender, male patients were the majority in both the SA group and the CA group. The mean age of the CA group was significantly higher than that of the SA group (46.11 ± 16.68 vs. 35.14 ± 13.8, respectively, P < 0.001). The mean IGC, IGC/N and CRP values were significantly higher in the CA group than in the SA group (P < 0.001 in each parameter). In addition, the mean WBC, NLR, PLR, IG% values were significantly higher in the CA group than in the SA group. The comparison between the CA and SA groups is shown in Table 2.

Table 2: Comparison of demographic and laboratory parameters between groups

The effectiveness of WBC, CRP, IGC, IG%, and IGC/N parameters in diagnosing AA and in differentiating CA from SA was calculated by plotting ROC curves [Figures 1 and 2]. The ability of IGC to predict AA was greater than that of other parameters. At a cutoff value of 15, which is the optimum cutoff value for IGC, the sensitivity was 98.3% and the specificity was 80%. Moreover, this showed that the sensitivity was higher than CRP and the specificity was close to CRP [Table 3]. At a cutoff value of 0.085, which is the optimum cutoff value for IGC/N, the sensitivity was 63.9% and the specificity was 72.3%. The sensitivity and specificity for the optimum cutoff value of IGC/N ratio in showing CA were similar to CRP [Table 4].

Figure 1: Receiver operating characteristic curve analysis of laboratory parameters in the discrimination between positive appendectomy and negative appendectomy groups

Figure 2: Receiver operating characteristic curve analysis of laboratory parameters in the discrimination between simple appendicitis and complicated appendicitis

Table 3: Receiver operating characteristics analysis of parameters for the prediction of acute appendicitis

Table 4: Receiver operating characteristics analysis of parameters for the prediction of complicated appendicitis

DISCUSSION

AA is a disease which is most commonly suspected and may require urgent surgical intervention in patients presenting to the emergency department with abdominal pain. In the initial evaluation of these patients, a comprehensive anamnesis and physical examination are followed by blood tests.[¹⁰¹¹] Despite advanced imaging and laboratory tests, it is complicated by perforation in 18%–34% of AA cases.[¹²] As CA rates increase, the mortality, morbidity, length of hospital stay, and medical cost will increase.[⁷] Therefore, biomarkers that can be used both in the diagnosis of AA and in the early diagnosis of complications are needed.

In the diagnosis of AA, increased WBC count, CRP, and ESR are important, but not diagnostic.[¹³] NLR and PLR are inexpensive, simple parameters that can be studied in almost any center and have recently been used in many diseases, including inflammatory conditions.[¹⁴¹⁵] In a recent study, NLR was found to be a useful parameter in the diagnosis of AA and in the differentiation between CA and SA. In this study, it was demonstrated that NLR is a useful parameter in the diagnosis of AA with a sensitivity of 73.3% and a specificity of 69.2% at a cutoff value of 3.5 and in the differentiation between CA and SA with a sensitivity of 79.1% and a specificity of 61.1% at a cutoff value of 5.6.[⁷] In a study of 102 patients by Kim et al., it was indicated that only CRP was statistically significant, although WBC and CRP were found to be higher in the CA group than in the SA group.[¹⁶] Moreover, in this study, serum delta neutrophil and myeloperoxidase index helped differentiate acute CA from uncomplicated appendicitis. The studies by Aydin et al. and Beecher et al. showed increased probability of CA in cases where NLR and CRP levels were high.[¹⁷¹⁸] In our study, a NLR of >3.62 supported the diagnosis of AA and a NLR of >5.08 supported the diagnosis of CA. We suggest that WBC, NLR, and PLR are more suitable because they are more sensitive in showing AA complications.

IG is a routine CBC parameter that is automatically measured by an automated blood cell analyzer and is recently begun to be used as a new inflammatory biomarker.[¹⁹²⁰] This measures the fraction of immature circulating granulocytes or, in other words, the increase in myeloid cell production. These cells are an indicator of inflammation.[⁹²¹] In a study by Kim et al., it was reported that IG% had a sensitivity of 25% and a specificity of 96.7% in predicting CA at a cut-off value of 5%.[²²] In a study by Mathews et al., the mean IG% was significantly higher in CAs than in SAs (0.34 ± 0.14 vs. 0.29 ± 0.19, respectively, P = 0.02).[²³] In a study by Shin et al., it was reported that IG% showed a sensitivity of 67.7% and a specificity of 90% in predicting CA at a cutoff value of 1.4.[²⁴] In a study of 412 patients conducted in 2018, WBC, NLR, IGC, IG% were reported to be a parameter that can be used both in the diagnosis of AA and to show complication. In this study, it was shown that IGC was more specific in the diagnosis of AA compared to other parameters area under the receiver operating characteristic curve (AUC): 0.795, sensitivity: 55.5%, specificity: 96.1%), and IG% could predict CA better than other parameters (AUC: 0.979, sensitivity: 94.4%, specificity: 97.9%).[⁷] However, the role of CRP in diagnosing AA and showing complication was not indicated in this study. In our study, we demonstrated the effectiveness of WBC, CRP, IGC, IG%, and IGC/N parameters in diagnosing AA and differentiating between CA and SA. To the best of our knowledge, there is no study including IGC/N ratio in the literature. In our study, we found that the ability of IGC to predict AA was greater than that of other parameters. At a cutoff value of 15, which is the optimum cutoff value for IGC, the sensitivity was 98.3% and the specificity was 80%. CRP and IGC/N ratio had the highest predictive values in differentiating between SA and CA. At a cutoff value of 0.085, which is the optimum cutoff value for IGC/N 0.085, the sensitivity was 63.9%, and the specificity was 72.3%.

Our study had some limitations. The first is the retrospective design of our study. The second is that it was not possible to include the time from onset of symptoms to the collection of samples, which is an important limitation as it may affect inflammation. Since the measurement of the IG parameter in the CBC was not available before March 2019, this study included cases after that date. Thus, the number of patients was limited. In addition, clinical symptoms and physical examination other than laboratory findings were not analyzed in this study.

CONCLUSION

IG is a routine CBC parameter that is rapid and does not incur additional cost to the patient. Based on the results of our study, we can speculate that IGC is a reliable marker in the diagnosis of AA. An IGC value of >15 in routine CBC is an important and early indicator in the diagnosis of AA but immature granulocytes and derivatives (IGC, IG%, and IGC/N) cannot be used for predicting CA because of low sensitivity and specificity.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.