Description of Irritable Bowel Syndrome (IBS)

Irritable bowel syndrome (IBS) is a common problem that affects the large intestine and causes abdominal cramping, bloating and a change in bowel habits. See MedlinePlus® - Health Topics - Irritable Bowel Syndrome for more information.

Background Information

IBS is a difficult condition to investigate in population-based research because there is no single diagnostic test to confirm disease presence and the symptoms of IBS may also be associated with other conditions, including infections.

The Rome criteria have been developed to provide physicians with a systematic methodology to classify individuals with functional gastrointestinal disorders, including IBS (Thompson et al., 2002). These criteria evolved from the work by Manning et al. (1978) which are provided in Table 1 (Yale et al., 2008, Rome Foundation). All Rome I, Rome II and Rome III criteria, the latter being the most recently developed criteria are available to physicians.

Literature Review

The following four studies provide descriptions of how IBS is defined in the literature.

1. Lix et al. (2010)

Lix et al. (2010) used records for both inpatient hospitalizations (from hospital abstracts data) and outpatient billing claims (medical services data) to identify IBS cases from Manitoba administrative data. Both ICD-9-CM codes and ICD-10-CA were used to identify IBS cases:


• ICD-9-CM code: 564.1
  
• ICD-10-CA code: K58

Because IBS is likely to be underreported in administrative data, Lix used other relevant diagnosis and procedure codes for initial case finding from inpatient hospitalizations and outpatient billing claims data. Diagnosis and procedure codes selected for identifying IBS cases are listed in Table 2.

Two case-ascertainment algorithms were investigated. For the first, Manitoba health insurance registrants were identified as IBS cases if they had at least one IBS diagnosis in hospital or physician data in a one-year period. For the second method, registrants were identified as IBS cases if they had at least one IBS diagnosis in a three-year period. One-year estimates were based on data for the 2004/05 fiscal year and three-year estimates were based on data from fiscal years 2002/03 to 2004/05.

In the study by Lix et al. (2010) population-based administrative data and survey data for IBS diagnoses were compared. The survey interview schedule included the following directions: "Now I'd like to ask about certain chronic health conditions which you may have. We are interested in 'long-term conditions' that have lasted or are expected to last six months or more and that have been diagnosed by a health professional." Respondents were asked whether they had ever been diagnosed with a number of chronic conditions, including a bowel disorder, specifically: "Do you suffer from a bowel disorder such as Crohn's disease, ulcerative colitis, irritable bowel syndrome, or bowel incontinence?" If the response was affirmative, respondents were asked to identify the type of bowel disorder with which they had been diagnosed: Crohn's disease, ulcerative colitis, irritable bowel syndrome bowel incontinence, or other bowel disorder (type was not specified).

Agreement was investigated for two periods of time both before and after the survey interview date, and results indicated that agreement was low. Agreements for 3 years before and 1 year after the interview date was 0.22 (%95 CI, 0.22, 0.23) and 0.11 (95% CI, 0.11, 0.12) consecutively.

2. Goff et al. (2008)

Goff et al. (2008), uses a retrospective study sample consisting of patients aged 18 years or above who are enrolled in nine geographically dispersed health plans participating in the HMO Research Network Centre for Education and Research on Therapeutics. ICD-9-CM code 564.1 for IBS is used for both inpatient and outpatient services between May 1, 2002 and September 15, 2002. Patients who have the following diagnosis were excluded from the study because symptoms might overlap with IBS:


• Crohn's disease, ulcerative colitis, ischemic colitis, microscopic or collagenous colitis, pseudo-membranous colitis, iron deficiency anemia, rectal bleeding, colon cancer, or weight loss.

Goff proposed 5 chart review selection criteria for identification of potential cases of IBS (see Table 3.)

3. Legorreta et al. (2002)

Legorreta et al. (2002) defined IBS based on the presence of at least one claim with an ICD-9-CM code 564.1. HMO administrative database were used to identify potential patients with IBS between January 1, 1998 and December 31, 1998.

Diagnosis claims that presents similar symptoms of IBS are excluded. The excluded diagnosis ICD-9-CM codes are as follows:


• 555.xx: Crohn's disease
  
• 556.xx: Ulcerative colitis
  
• 558.xx: Enteritis/ inflammatory bowel disease
  
• 150.xx - 159.xx, 197.8, 199.x or 234.9: GI cancer

4. Sands et al. (2006)

In the study by Sands et al. (2006), claims-based algorithms to identify colonic ischemia, hospitalized complications of constipation, and irritable bowel syndrome (IBS) were validated.

ICD-9-CM code for IBS, Irritable colon is 564.1 (associated with facility or physician service).

The research database is comprised of four components:


1. An enrollment database with demographic information
   
2. A medical claims database, consisting of records from all health care sites for virtually all types of services provided to enrollees, including physician specialty, preventive and office-based treatments
   
3. An outpatient pharmacy dispensing claims database
   
4. Laboratory files that capture the results of a variety of outpatient tests.

Medical chart data were abstracted and reviewed to accurately identify true cases of each condition of interest. The criteria for IBS were:


• Findings typical of classic diagnostic criteria (Rome or Manning criteria)
  
• No alternative diagnoses accounting for patient's symptoms, based upon diagnostic studies such as lower endoscopy, colonic biopsy, or laboratory studies.

The study sample consists of patients aged 20 years or older who had at least one day of health plan enrollment during the period of 1 January 1995 to 31 December 1999.