The Rome III Criteria for functional constipation must include two or more of the following and present for the past three months, with symptoms starting for at least 6 months prior to diagnosis.

- Straining during defecation for at least 25% of bowel movements

- Lumpy or hard stools in at least 25% of defecations

- Sensation of incomplete evacuation for at least 25% of defecations

- Sensation of anorectal obstruction/blockage for at least 25% of defecations

- Manual maneuvers to facilitate at least 25% of defecations

- Fewer than 3 defecations per week

- Loose stools are rarely present without the use of laxatives

- There are insufficient criteria for irritable bowel syndrome

Functional constipation is common and does not warrant diagnostic testing. Imaging and laboratory tests are typically recommended for those with alarm signs or symptoms.

The laboratory tests performed depends on the suspected underlying cause of the constipation. Tests may include CBC (complete blood count), thyroid function tests, serum calcium, serum potassium, etc.

Abdominal X-rays are generally only performed if bowel obstruction is suspected, may reveal extensive impacted fecal matter in the colon, and may confirm or rule out other causes of similar symptoms.

Colonoscopy may be performed if an abnormality in the colon like a tumor is suspected. Other tests rarely ordered include anorectal manometry, anal sphincter electromyography, and defecography.

Colonic propagating pressure wave sequences (PSs) are responsible for discrete movements of the bowel contents and are vital for normal defecation. Deficiencies in PS frequency, amplitude, and extent of propagation are all implicated in severe defecatory dysfunction (SDD). Mechanisms that can normalize these aberrant motor patterns may help rectify the problem. Recently the novel therapy of sacral nerve stimulation (SNS) has been utilized for the treatment of severe constipation.

A 2014 meta-analysis of three small trials evaluating probiotics showed a slight improvement in management of chronic idiopathic constipation, but well-designed studies are necessary to know the true efficacy of probiotics in treating this condition.

Children with functional constipation often claim to lack the sensation of the urge to defecate, and may be conditioned to avoid doing so due to a previous painful experience. One retrospective study showed that these children did indeed have the urge to defecate using colonic manometry, and suggested behavioral modification as a treatment for functional constipation.

There is considerable research into the causes, diagnosis and treatments for FGIDs. Diet, microbiome, genetics, neuromuscular function and immunological response all interact. Heightened mast cell activation has been proposed to be a common factor among FGIDs, contributing to visceral hypersensitivity as well as epithelial, neuromuscular, and motility dysfunction.

Gastroparesis can be diagnosed with tests such as x-rays, manometry, and gastric emptying scans. The clinical definition for gastroparesis is based solely on the emptying time of the stomach (and not on other symptoms), and severity of symptoms does not necessarily correlate with the severity of gastroparesis. Therefore, some patients may have marked gastroparesis with few, if any, serious complications.

Investigations are performed to exclude other conditions:

- Stool microscopy and culture (to exclude infectious conditions)

- Blood tests: Full blood examination, liver function tests, erythrocyte sedimentation rate, and serological testing for coeliac disease

- Abdominal ultrasound (to exclude gallstones and other biliary tract diseases)

- Endoscopy and biopsies (to exclude peptic ulcer disease, coeliac disease, inflammatory bowel disease, and malignancies)

- Hydrogen breath testing (to exclude fructose and lactose malabsorption)

No specific laboratory or imaging test can be performed to diagnose irritable bowel syndrome. Diagnosis involves excluding conditions that produce IBS-like symptoms, and then following a procedure to categorize the patient's symptoms. Ruling out parasitic infections, lactose intolerance, small intestinal bacterial overgrowth, and celiac disease is recommended for all patients before a diagnosis of irritable bowel syndrome is made. In patients over 50 years old, they are recommended to undergo a screening colonoscopy. IBS sufferers are at increased risk of being given inappropriate surgeries such as appendectomy, cholecystectomy, and hysterectomy due to their IBS symptoms being misdiagnosed as other medical conditions.

Reducing opiate-based medication (when possible, tolerable, and safe; prescription medication changes should be done under the supervision of a physician), and adequate intake of liquids (water) and dietary fiber and daily exercise.

Chronic idiopathic constipation is similar to constipation-predominant irritable bowel syndrome (IBS-C); however, people with CIC do not have other symptoms of IBS, such as abdominal pain. Diagnosing CIC can be difficult as other syndromes must be ruled out as there is no physiological cause for CIC. Doctors will typically look for other symptoms, such as blood in stool, weight loss, low blood count, or other symptoms.

To be considered functional constipation, symptoms must be present at least a fourth of the time.

Possible causes are:

- Anismus

- Descending perineum syndrome

- Other inability or unwillingness to control the external anal sphincter, which normally is under voluntary control

- A poor diet

- An unwillingness to defecate

- Nervous reactions, including prolonged and/or chronic stress and anxiety, that close the internal anal sphincter, a muscle that is not under voluntary control

- Deeper psychosomatic disorders which sometimes affect digestion and the absorption of water in the colon

There is also possibility of presentation with other comorbid symptoms such as headache, especially in children.

The psychiatric (DSM-IV) diagnostic criteria for encopresis are:

1. Repeated passage of feces into inappropriate places (e.g., underwear or floor) whether voluntary or unintentional

2. At least one such event a month for at least 3 months

3. Chronological age of at least 4 years (or equivalent developmental level)

4. The behavior is not exclusively due to a physiological effect of a substance (e.g., laxatives) or a general medical condition, except through a mechanism involving constipation.

The DSM-IV recognizes two subtypes: with constipation and overflow incontinence, and without constipation and overflow incontinence. In the subtype with constipation, the feces are usually poorly formed and leakage is continuous, and this occurs both during sleep and waking hours. In the type without constipation, the feces are usually well-formed, soiling is intermittent, and feces are usually deposited in a prominent location. This form may be associated with oppositional defiant disorder (ODD) or conduct disorder, or may be the consequence of large anal insertions, or more likely due to chronic encopresis that has radically desensitized the colon and anus.

Attempts must be made to determine whether there is a secondary cause amenable to treatment.

Primary (idiopathic) intestinal pseudo-obstruction is diagnosed based on motility studies, x-rays and gastric emptying studies.

Many pediatricians will recommend the following three-pronged approach to the treatment of encopresis associated with constipation:

1. cleaning out

2. using stool softening agents

3. scheduled sitting times, typically after meals.

The initial clean-out is achieved with enemas, laxatives, or both. The predominant approach today is the use of oral stool softeners like Movicol, Miralax, Lactulose, mineral oil, etc. Following that, enemas and laxatives are used daily to keep the stools soft and allow the stretched bowel to return to its normal size.

The child must be taught to use the toilet regularly to retrain his/her body. It is usually recommended that a child be required to sit on the toilet at a regular time each day and 'try' to go for 10–15 minutes, usually soon (or immediately) after eating. Children are more likely to be able to expel a bowel movement right after eating. It is thought that creating a regular schedule of bathroom time will allow the child to achieve a proper elimination pattern. Repeated voiding success on the toilet itself helps it become a releasor stimulus for successful bowel movements.

Alternatively, when this method fails for six months or longer, a more aggressive approach may be undertaken using suppositories and enemas in a carefully programmed way to overcome the reflexive holding response and to allow the proper voiding reflex to take over. Failure to establish a normal bowel habit can result in permanent stretching of the colon. Certainly, allowing this problem to continue for years with constant assurances that the child "will grow out of it" should be avoided.

Dietary changes are an important management element. Recommended changes to the diet in the case of constipation-caused encopresis include:

1. reduction in the intake of constipating foods such as dairy, peanuts, cooked carrots, and bananas

2. increase in high-fiber foods such as bran, whole wheat products, fruits, and vegetables

3. higher intake of water and liquids, such as juices, although an increased risk of tooth decay has been attributed to excess intake of sweetened juices

4. limit drinks with caffeine, including cola drinks and tea

5. provide well-balanced meals and snacks, and limit fast foods/junk foods that are high in fats and sugars

6. limit whole milk to 500 mL (16.9 ounces) a day for the child over 2 years of age, but do not completely eliminate milk because children need calcium for bone growth and strength.

The standard behavioral treatment for functional encopresis, which has been shown to be highly effective, is a motivational system such as a contingency management system. In addition to this basic component, seven or eight other behavioral treatment components can be added to increase effectiveness.

Doctors can diagnose proctitis by looking inside the rectum with a proctoscope or a sigmoidoscope. A biopsy is taken, in which the doctor scrapes a tiny piece of tissue from the rectum, and this tissue is then examined by microscopy. The physician may also take a stool sample to test for infections or bacteria. If the physician suspects that the patient suffers from Crohn's disease or ulcerative colitis, colonoscopy or barium enema X-rays are used to examine areas of the intestine.

The treatment of fecal impaction requires both the remedy of the impaction and treatment to prevent future recurrences. Decreased motility of the colon results in dry, hard stools that in the case of fecal impaction become compacted into a large, hard mass of stool that cannot be expelled from the rectum.

Various methods of treatment attempt to remove the impaction by softening the stool, lubricating the stool, or breaking it into pieces small enough for removal. Enemas and osmotic laxatives can be used to soften the stool by increasing the water content until it is soft enough to be expelled. Osmotic laxatives such as magnesium citrate work within minutes - 8 hours for onset of action, and even then they may not be sufficient to expel the stool.

Osmotic laxatives can cause cramping and even severe pain as the patient's attempts to evacuate the contents of the rectum are blocked by the fecal mass. Polyethylene glycol (PEG 3500) may be used to increase the water content of the stool without cramping; however, since it may take 24 to 48 hours for it to take effect, it is not well suited to cases where the impaction needs to be removed immediately due to risk of complications or severe pain. Enemas (such as hyperosmotic saline) and suppositories (such as glycerine suppositories) work by increasing water content and stimulating peristalsis to aid in expulsion, and both work much more quickly than oral laxatives.

Because enemas work in 2–15 minutes, they do not allow sufficient time for a large fecal mass to soften. Even if the enema is successful at dislodging the impacted stool, the impacted stool may remain too large to be expelled through the anal canal. Mineral oil enemas can assist by lubricating the stool for easier passage. In cases where enemas fail to remove the impaction, polyethylene glycol can be used to attempt to soften the mass over 24–48 hours, or if immediate removal of the mass is needed, manual disimpaction may be used. Manual disimpaction may be performed by lubricating the anus and using one gloved finger with a scoop-like motion to break up the fecal mass. Most often manual disimpaction is performed without general anaesthesia, although sedation may be used. In more involved procedures, general anaesthesia may be used, although the use of general anaesthesia increases the risk of damage to the anal sphincter. If all other treatments fail, surgery may be necessary.

Individuals who have had one fecal impaction are at high risk of future impactions. Therefore, preventative treatment should be instituted in patients following the removal of the mass. Increasing dietary fiber, increasing fluid intake, exercising daily, and attempting regularly to defecate every morning after eating should be promoted in all patients.

Often underlying medical conditions cause fecal impactions; these conditions should be treated to reduce the risk of future impactions. Many types of medications (most notably opioid pain medications, such as codeine) reduce motility of the colon, increasing the likelihood of fecal impactions. If possible, alternate medications should be prescribed that avoid the side effect of constipation.

Given that all opioids can cause constipation, it is recommended that any patient placed on opioid pain medications should be given medications to prevent constipation before it occurs. Daily medications can also be used to promote normal motility of the colon and soften stools. Daily use of laxatives or enemas should be avoided by most individuals as it can cause the loss of normal colon motility. However, for patients with chronic complications, daily medication under the direction of a physician may be needed.

Polyethylene glycol 3350 can be taken daily to soften the stools without the significant risk of adverse effects that are common with other laxatives. In particular, stimulant laxatives should not be used frequently because they can cause dependence in which an individual loses normal colon function and is unable to defecate without taking a laxative. Frequent use of osmotic laxatives should be avoided as well as they can cause electrolyte imbalances.

Treatment includes dietary changes (low fiber diets) and, in some cases, restrictions on fat and/or solids. Eating smaller meals, spaced two to three hours apart has proved helpful. Avoiding foods that cause the individual problems, such as pain in the abdomen, or constipation, such as rice or beef, will help avoid symptoms.

Metoclopramide, a dopamine D receptor antagonist, increases contractility and resting tone within the GI tract to improve gastric emptying. In addition, dopamine antagonist action in the central nervous system prevents nausea and vomiting. Similarly, the dopamine receptor antagonist domperidone is also used to treat gastroparesis. Erythromycin is known to improve emptying of the stomach but its effects are temporary due to tachyphylaxis and wane after a few weeks of consistent use.

Sildenafil citrate, which increases blood flow to the genital area in men, is being used by some practitioners to stimulate the gastrointestinal tract in cases of diabetic gastroparesis.

The antidepressant mirtazapine has proven effective in the treatment of gastroparesis unresponsive to conventional treatment. This is due to its antiemetic and appetite stimulant properties. Mirtazapine acts on the same serotonin receptor (5-HT3) as does the popular anti-emetic ondansetron.

In specific cases where treatment of chronic nausea and vomiting proves resistant to drugs, implantable gastric stimulation may be utilized. A medical device is implanted that applies neurostimulation to the muscles of the lower stomach to reduce the symptoms. This is only done in refractory cases that have failed all medical management (usually at least 2 years of treatment). Medically refractory gastroparesis may also be treated with a pyloromyotomy, which widens the gastric outlet by cutting the circular pylorus muscle. This can be done laparoscopically or endoscopically.

Functional gastrointestinal disorders are very common. Globally, irritable bowel syndrome and functional dyspepsia alone may affect 16–26% of the population.

Physical examination can rule out anismus (by identifying another cause) but is not sufficient to diagnose anismus.

For severe constipation which has not responded to laxatives, dietary supplements or other lifestyle changes. Measures the patients ability to propel a stool through the anal canal. A simulated stool (balloon) is inserted into the rectum with the patient lying on his/her side, and the patient is asked to push the balloon out as they would a stool. Used to assess muscle strength and coordination.

Secondary chronic intestinal pseudo-obstruction is managed by treating the underlying condition.

There is no cure for primary chronic intestinal pseudo-obstruction. It is important that nutrition and hydration is maintained, and pain relief is given. Drugs that increase the propulsive force of the intestines have been tried, as have different types of surgery.

Diagnosis is achieved mainly by plain and contrasted radiographical and ultrasound imaging. Colonic marker transit studies are useful to distinguish colonic inertia from functional outlet obstruction causes. In this test, the patient swallows a water-soluble bolus of radio-opaque contrast and films are obtained 1, 3 and 5 days later. Patients with colonic inertia show the marker spread throughout the large intestines, while patients with outlet obstruction exhibit slow accumulations of markers in some places. A colonoscopy can also be used to rule out mechanical obstructive causes. Anorectal manometry may help to differentiate acquired from congenital forms. Rectal biopsy is recommended to make a final diagnosis of Hirschsprung disease.

Identification of the exact causes usually begins with a thorough medical history, including detailed questioning about symptoms, bowel habits, diet, medication and other medical problems. Digital rectal examination is performed to assesses resting pressure and voluntary contraction (maximum squeeze) of the sphincter complex and puborectalis. Anal sphincter defects, rectal prolapse, and abnormal perineal descent may be detected. Anorectal physiology tests assess the functioning of the anorectal anatomy. Anorectal manometry records the pressure exerted by the anal sphincters and puborectalis during rest and during contraction. The procedure is also able to assess sensitivity of the anal canal and rectum. Anal electromyography tests for nerve damage, which is often associated with obstetric injury. Pudendal nerve terminal motor latency tests for damage to the pudendal motor nerves. Proctography, also known as defecography, shows how much stool the rectum can hold, how well the rectum holds it, and how well the rectum can evacuate the stool. It will also highlight defects in the structure of the rectum such as internal rectal intussusception. Dynamic pelvic MRI, also called MRI defecography is an alternative which is better for some problems but not as good for other problems. Proctosigmoidoscopy involves the insertion of an endoscope (a long, thin, flexible tube with a camera) into the anal canal, rectum and sigmoid colon. The procedure allows for visualization of the interior of the gut, and may detect signs of disease or other problems that could be a cause, such as inflammation, tumors, or scar tissue. Endoanal ultrasound, which some consider to be the gold standard for detection of anal canal lesions, evaluates the structure of the anal sphincters, and may detect occult sphincter tears that otherwise would go unseen.

Functional FI is common. The Rome process published diagnostic criteria for functional FI, which they defined as "recurrent uncontrolled passage of fecal material in an individual with a developmental age of at least 4 years". The diagnostic criteria are, one or more of the following factors present for the last 3 months: abnormal functioning of normally innervated and structurally intact muscles, minor abnormalities of sphincter structure/innervation (nerve supply), normal or disordered bowel habits, (i.e., fecal retention or diarrhea), and psychological causes. Furthermore, exclusion criteria are given. These are factors which all must be excluded for a diagnosis of functional FI, and are abnormal innervation caused by lesion(s) within the brain (e.g., dementia), spinal cord (at or below T12), or sacral nerve roots, or mixed lesions (e.g., multiple sclerosis), or as part of a generalized peripheral or autonomic neuropathy (e.g., due to diabetes), anal sphincter abnormalities associated with a multisystem disease (e.g., scleroderma), and structural or neurogenic abnormalities that are the major cause.

Bile acid malabsorption is common in Crohn's disease but not always recognised. Most patients with previous ileal resection and chronic diarrhea will have abnormal SeHCAT tests and can benefit from bile acid sequestrants.

Patients with primary bile acid diarrhea are frequently misdiagnosed as having the irritable bowel syndrome as clinicians fail to recognize the condition. When SeHCAT testing is performed, the diagnosis of primary bile acid diarrhea is commonly made. In a review of 18 studies of the use of SeHCAT testing in diarrhea-predominant irritable bowel syndrome patients, 32% of 1223 patients had a SeHCAT 7-day retention of less than 10%, and 80% of these reported a response to cholestyramine, a bile acid sequestrant.

Estimates of the population prevalence taken from this review suggest that 1% of the adult population could have primary bile acid diarrhea (Type 2 bile acid malabsorption).

The two key features of obstructed defecation are:

1. An inability to voluntarily evacuate rectal contents

2. Normal colonic transit time

A 5 item questionnaire was validated for diagnosis and grading of obstructed defecation syndrome. The parameters were:

1. Excessive straining

2. Incomplete rectal evacuation

3. Use of enemas and/or laxatives

4. Vaginal-anal-perineal digitations (needing to press in the back wall of the vagina or on the perineum to aid defecation)

5. Abdominal discomfort and/or pain

Treatment for proctitis varies depending on severity and the cause. For example, the physician may prescribe antibiotics for proctitis caused by bacterial infection. If the proctitis is caused by Crohn's disease or ulcerative colitis, the physician may prescribe the drug 5-aminosalicyclic acid (5ASA) or corticosteroids applied directly to the area in enema or suppository form, or taken orally in pill form. Enema and suppository applications are usually more effective, but some patients may require a combination of oral and rectal applications.

Another treatment available is that of fiber supplements such as Metamucil. Taken daily these may restore regularity and reduce pain associated with proctitis.

Several severity scales exist. The Cleveland Clinic (Wexner) fecal incontinence score takes into account five parameters that are scored on a scale from zero (absent) to four (daily) frequency of incontinence to gas, liquid, solid, of need to wear pad, and of lifestyle changes. The Park's incontinence score uses four categories:

The fecal incontinence severity index is based on four types of leakage (gas, mucus, liquid stool, solid stool) and five frequencies (once to three times per month, once per week, twice per week, once per day, twice or more per day). Other severity scales include: AMS, Pescatori, Williams score, Kirwan, Miller score, Saint Mark's score and the Vaizey scale.