Search and critical appraisal

Search results and study selection are described in Fig. 1. A total of twelve articles were critically appraised [9,10,11,12,13,14,15,16,17,18,19,20]. Most studies were rated as reasonable to good quality based on the cross-sectional appraisal tool from wordpress.com and the SIGN Methodology Checklist [8] http://www.sign.ac.uk/pdf/sign50annexc.pdf. Studies were mostly downgraded due to lack of control of possible confounders. None of the studies were graded high quality since the studies were of retrospective design and/or had small patient numbers and/or poor presentation of results. The results of the critical appraisal are depicted in Table 1.

Table 1 Study characteristics Full size table

Baseline characteristics

Study characteristics of the included studies are shown in Table 1. Of the twelve included studies, four had a retrospective cross-sectional design [14,15,16, 19] and seven had a retrospective cohort design [9,10,11,12,13, 17, 20]. There was one prospective cross-sectional study [18]. The 12 included articles evaluated a total of 4619 patients with diverticulitis. In all studies, the diagnosis (complicated) diverticulitis was proven by computed tomography (CT) or pathological examination. A total of 3661 (79%) patients had uncomplicated diverticulitis and 958 (21%) had complicated diverticulitis.

Main outcome—risk factors for complicated diverticulitis

Age

Ten studies reported on age as a risk factor for complicated diverticulitis [10,11,12,13,14,15,16,17, 19, 20]. A pooled data analysis was performed on studies that reported age as a dichotomous variable (older or younger than 50 years) [10,11,12,13, 17, 20]. The pooled analysis showed no significant difference. The pooled risk ratio was 0.74 (95% CI 0.27–2.02) in a random effects model (I 2 = 95%), as depicted in Fig. 2. Makela et al. reported the influence of age on the risk for complicated diverticulitis in three groups (< 50, 50–70, and > 70 years). They found a significant effect of old age (> 70 years) on the risk of complicated diverticulitis (p = 0.008) [15].

Fig. 2 Meta-analysis. Age ≤ 50 and > 50 years Full size image

Pooling of studies that described age as a continuous variable (mean and standard deviation) was not possible due to the fact some studies did not report the required standard deviation of the mean age. There was no consensus among these studies on the effect of age on the severity of diverticulitis. Van de Wall et al. found that patients with complicated diverticulitis were of a significantly (p < 0.05) higher age (63.9 years) as compared with patients with an uncomplicated episode (57.1 years) [19]. Nizri et al. and Longstreth et al. however did not find a significant effect. They respectively found a mean age of 63 and 57.3 years in patients with an uncomplicated episode compared to 59.3 and 56.6 years in patients with complicated diverticulitis (p = 0.182 and 0.71, respectively) [14, 16].

Gender

Four studies reported on gender [14,15,16, 19]. Pooled analysis demonstrated no significant difference in risk for complicated diverticulitis. The pooled risk ratio was 0.85 (95% CI 0.69–1.06) in a random effects model (I 2 = 60%), as depicted in Fig. 3. The absolute risk of developing complicated diverticulitis varied from 9 to 46% in women with an estimated average of 21%. In men, the absolute risk of developing complicated diverticulitis varied from 16 to 59% with an estimated average of 25%.

History of previous attacks

Two studies reported on history of previous attacks as a risk factor for complicated diverticulitis [16, 19]. Nizri et al. found that a primary episode of diverticulitis was at greater risk to be accompanied by complications compared to recurrent episodes (RR 1.98, 95% CI 1.26–3.11) [16]. Van de Wall et al. did not find a significant effect of previous attacks on the severity of diverticulitis. Twelve percent of the patients who presented with uncomplicated diverticulitis had had previous attacks, compared to 14% of the patients presenting with complicated diverticulitis [19].

Clinical signs and physical examination

Three studies reported on clinical signs (such as nausea, vomiting, bloating) as risk factors for complicated diverticulitis [14, 18, 19]. Longstreth et al. found that significantly more patients with complicated diverticulitis had signs of constipation (OR 2.32, 95% CI 1.27–4.23). Furthermore, patients with complicated diverticulitis presented less frequently with localized pain in the lower left abdomen (OR 0.54, 95% CI 0.29–0.99). These patients had more generalized abdominal pain [14].

Van de Wall et al. found that patients with a complicated episode presented more frequently with vomiting (26 versus 11%) and diffuse abdominal pain (20 versus 9%) than patients with an uncomplicated episode [19].

Tursi et al. investigated the severity of symptoms in uncomplicated and complicated diverticulitis graded on a quantitative scale. They found that patients with complicated diverticulitis had more severe constipation, abdominal pain, and, when present, more severe rectal blood loss [18].

Body temperature

Body temperature at presentation was reported in three studies. Tursi et al. found that a temperature greater than 37 °C was associated with complicated diverticulitis. Almost all patients (9 out of 11) with complicated diverticulitis presented with a temperature greater than 37 °C while all the patients with uncomplicated diverticulitis (39 out of 39) had a temperature below 37 °C [18].

Longstreth et al. demonstrated that patients presenting with a temperature greater than 37.5 °C had a higher risk of having complicated diverticulitis (OR 2.13, 95% CI 1.27–3.57). Van de Wall reported on mean body temperature and did not find a significant effect. The mean temperature in patients with uncomplicated diverticulitis was 37.5 °C (36.2–38.9) and 37.6 °C (36.3–39.0) for complicated cases [14].

C-reactive protein

Four studies reported on CRP level as a risk factor for complicated diverticulitis [15, 16, 18, 20]. All studies found a significant effect of CRP level on the risk of complicated diverticulitis. The overall mean CRP among patients with uncomplicated diverticulitis was 68 mg/L with a range of 25 to 96 mg/L. This was 186 mg/L with a range of 134 to 224 mg/L among patients with complicated diverticulitis.

Three studies calculated the optimal threshold value of CRP level to distinguish uncomplicated from complicated diverticulitis. Makela et al. found an optimal cutoff point of 149.5 mg/L (sensitivity 65%, specificity 85%) [15]. The studies of Nizri et al. and van de Wall et al. found an optimal cutoff point of 90 mg/L (sensitivity 88%, specificity 75%) and 175 mg/L (sensitivity 61%, specificity 82%), respectively [16, 19].

White blood cell count

Four studies reported on this risk factor [14, 15, 18, 19]. Tursi et al. and van de Wall et al. reported on WBC as a continuous variable showing a significant effect of WBC on the risk of complicated diverticulitis. Average mean WBC count was 10.4 × 109/L (range 8.7–12.0 × 109/L) in uncomplicated diverticulitis and 14.4 × 109/L (range 12.5–15.3 × 109/L) in complicated diverticulitis [18, 19].

Two studies reported WBC as a dichotomous value [14, 15]. Makela et al. reported a sensitivity of 51% and specificity of 46% for a cutoff value of 10 × 109/L (p = 0.672) [15]. Longstreth et al. found a sensitivity of 82% and specificity of 45% for a cutoff value of 11 × 109/L (p = < 0.0001) [14].

Body mass index

Only one study reported on body mass index (BMI) as a risk factor for complicated diverticulitis. Longstreth et al. found no significant difference between patients with a BMI greater or smaller than 25 (OR 1.00 (CI 0.96–1.04) [14].

Comorbidity

One study reported on comorbidity and found that the group of patients with complicated diverticulitis consisted of patients with a higher American Society of Anesthesiologists (ASA) classification (ASA I 26%; ASA II 65%; ASA III 10%) compared to the group with uncomplicated diverticulitis (ASA I 41%; ASA II 51%; ASA III 8%) [19].

Diabetes mellitus

The effect of diabetes mellitus (DM) on the risk of complicated diverticulitis was reported in one retrospective cohort study. Approximately 16% of the patients without DM had complicated diverticulitis compared to 27% of the patients with DM (p < 0.003) [9].

Steroid use and immunosuppression

One study reported on the use of steroids. Patients with complicated diverticulitis more frequently used steroids compared to patients with uncomplicated diverticulitis (7.3 versus 3.3%; p = 0.015) [16].