Background: Anti-Saccharomyces cerevisiae antibodies (ASCA) are a specific but only moderately sensitive diagnostic marker for Crohn’s disease. We sought to explore the role of ASCA as a prognostic marker for aggressive disease phenotype in Crohn’s disease.
Aims: To determine the role of ASCA status as a risk factor for early surgery in Crohn’s disease.
Subjects: We performed a case control study in a cohort of patients, newly diagnosed with Crohn’s disease, between 1991 and 1999. All patients were followed for at least three years. Case subjects (n = 35) included those who had major surgery for Crohn’s disease within three years of diagnosis. Controls (n = 35) included patients matched to cases for age, sex, disease location, and smoking status, and who did not undergo major surgery for Crohn’s disease within three years of diagnosis.
Methods: Blinded assays were performed on serum for ASCA (immunoglobulin (Ig)A and IgG). A paired analysis of cases-controls was performed to test for the association between ASCA status and risk of early surgery.
Results: ASCA IgA was strongly associated with early surgery (odds ratio (OR) 8.5 (95% confidence interval (CI) 2.0–75.9); p = 0.0013). ASCA IgG+ and ASCA IgG+/IgA+ patients were also at increased risk for early surgery (OR 5.5 (95% CI 1.2–51.1), p = 0.0265; and OR 5.0 (95% CI 1.1–46.9), p = 0.0433, respectively). The association between ASCA and early surgery was evident in patients requiring surgery for ileal or ileocolonic disease.
Conclusions: Patients with Crohn’s disease who are positive for ASCA IgA, IgG, or both, may define a subset of patients with Crohn’s disease at increased risk for early surgery.Keywords: Crohn’s disease, serology, surgery, case control study, inflammatory bowel disease
Medical therapy for Crohn’s disease (CD) is not curative, and relies on a variety of approaches to suppress bowel inflammation and the mucosal immune response. As reliable indicators of prognosis are lacking, medical therapy is usually guided by signs and symptoms. Treatment usually progresses sequentially through less effective therapies with few side effects, such as 5-aminosalicylates and antibiotics, to more efficacious therapies that may be associated with increased risk of serious adverse events, such as corticosteroids, immunomodulators, and anti-tumour necrosis factor (TNF) treatments.1
Despite this empiric approach to medical therapy, published data indicate that approximately 80% of CD patients require surgery by 20 years2 while 20–40% require their first surgery within three years of diagnosis.2–5 As resection is not curative, surgery is usually reserved for medically refractory disease, or for individuals with inflammatory sequelae such as stricture, fistula, or abscess. It is not known whether a more aggressive approach to medical therapy, such as treatment with immunomodulators or anti-TNF antibodies given soon after diagnosis, might alter the course of disease and decrease the rate of surgery. A limiting factor in such an approach is the poor ability to identify at the time of diagnosis those patients with an unfavourable prognosis. Given the increased risk of side effects associated with these medications, the risk-benefit analysis of this alternative approach would likely favour its application to the subgroup of patients at increased risk for poorer prognosis.
In 1988, Main et al observed that serum titres of both immunoglobulin (Ig)A and IgG antibodies against Saccharomyces cerevisiae (ASCA) were higher among patients with CD compared with controls.6Approximately 60% of CD patients may be found to have ASCA present.6–9 Despite this modest sensitivity, several studies have found ASCA expression (either IgA or IgG) to be nearly 95% specific for CD.8,10,11
In addition to its utility as a diagnostic marker for CD, more recent evidence suggests that ASCA serology may also correlate with disease behaviour. ASCA titres have been shown to be positively associated with early age of disease onset, fibrostenosis, and internal fistulas.12,13 Additional evidence suggests an association of ASCA with disease location, with a reported linkage to ileal involvement.13 Furthermore, among patients with CD with ileal involvement, ASCA has been associated with a higher incidence of small bowel surgery.12,13
In a cohort of patients in New England diagnosed with CD, we have found that 20% underwent early surgery (defined as occurring within three years of diagnosis, exclusive of surgery that was simultaneous with diagnosis).14 Baseline clinical characteristics independently associated with early surgery were disease location (decreased risk associated with isolated colonic localisation) and cigarette smoking (increased risk). The aim of this study was to determine if ASCA serological status is associated with increased risk for early surgery.Go to:
METHODS
Study population
A consortium of 16 investigative sites in New England (referral centres and community based physicians) characterised 345 patients diagnosed with CD between 1991 and 1999 and followed for at least three years.14 Diagnosis was confirmed according to standard radiographic, endoscopic, and histological criteria. Retrospective data collection was performed on baseline characteristics, medication use in the first three years, and incidence of surgery within three years of diagnosis.14
Among this cohort of 345 patients, 69 required major surgery within three years of diagnosis, excluding surgery performed at diagnosis. Major surgery was defined as any intra-abdominal surgical procedure, complex abscess drainage, or complex perianal fistula surgery performed for CD. Isolated incision and drainage of perianal abscess and simple perianal fistulectomy did not qualify as surgery in this outcome definition.
Written informed consent was obtained to collect blood for serology from 35 such “cases” (major surgery within three years of diagnosis, exclusive of surgery performed at diagnosis) from this cohort. Blood was drawn from 30 “controls” (no major surgery within three years of diagnosis) who were matched to cases on the basis of sex, age±7 years, location of disease, and smoking behaviour at the time of diagnosis. An additional five control subjects were enrolled from the personal practice of one of the authors (BES) when no match could be found within the cohort of 345 patients.
A sample of venous blood was drawn from each paired subject. Serum was separated by centrifugation and stored at −80°C. Blinded samples were sent to Prometheus Laboratories (San Diego, California, USA) for ASCA (IgA and IgG), DNAse sensitive perinuclear antineutrophil cytoplasmic antibody (pANCA), and anti-OmpC (Escherichia coli outer membrane porin C) Ig A testing.
Serological assays
ASCA
Standard ELISA assays were performed using an oligosaccharide mannan preparation derived from Saccharomyces uvarum. Results were reported as EU, a ratio of sample OD to that obtained with the standard. An ASCA IgA ELISA of greater than 20.0 EU/ml and an IgG ELISA of greater than 40.0 EU/ml were considered positive test results.
DNAse sensitive pANCA
Patient serum samples were screened for the presence of IgG anti-ANCA using an ELISA format with Ficoll-Hypaque gradient purified human neutrophils. Serum samples were applied to PMN coated slides and the presence of a peripheral pattern of staining was determined by immunofluorescence microscopy. Sera which were considered to be positive for DNase sensitive pANCA were positive on both ELISA screening and in addition were observed to have a DNAse sensitive immunofluorescence pattern.
Anti-OmpC
ELISA wells were coated with purified OmpC antigen. Patient samples, serum standard, and low and high serum controls were diluted 1:100 and added to the wells. After incubation and wash steps, the presence of bound human IgA antibodies was demonstrated with goat antihuman IgA-alkaline phosphatase antibody. An anti-OmpC IgA ELISA of greater than 16.5 EU/ml was considered a positive test result.
Statistical analysis
A two tailed McNemar’s test was used to compare paired proportions (matched cases and controls) of the frequency of positive serum values for ASCA, pANCA, and anti-OmpC. Results are reported as odds ratio (OR) and 95% confidence interval (CI), with p values. Statistically significant findings were identified at an alpha level of p⩽0.05. Correlations between ASCA titre and time from diagnosis to serology and between ASCA titre and time from surgery to serology were explored using Pearson’s correlation coefficient. Two tailed Fisher’s exact tests were used to obtain nominal p values for exploratory comparisons of baseline demographic and clinical features of the groups of patients comprising cases and controls. Exploratory analyses of the association of ASCA titre and risk of early surgery were performed using a Wilcoxon rank sum test. Cochran-Mantel-Haenszel tests were used to perform a stratified analysis of the risk of early surgery in association with ASCA while controlling for the presence or absence of pANCA and OmpC. The study was approved by the Institutional Review Board at the Massachusetts General Hospital.