Anorectal manometry is a diagnostic test that measures how well the muscles and nerves in your rectum and anal canal are working. A thin, flexible catheter with pressure sensors is inserted into the rectum to record muscle strength, reflexes, and sensation during a series of simple tasks like squeezing and bearing down. The test is most commonly ordered to investigate chronic constipation or fecal incontinence that hasn’t responded to basic treatments.
Why the Test Is Ordered
Chronic constipation and fecal incontinence are the two most common reasons for anorectal manometry, but the test serves a broader diagnostic role than many people realize. Constipation falls into different categories: some people have slow-moving bowels, while others have a coordination problem where the muscles that should relax during a bowel movement actually tighten instead. Standard imaging and blood work can’t distinguish between these, so manometry is often the only way to pinpoint the cause and determine whether targeted pelvic floor therapy would help.
For fecal incontinence, the test reveals whether the problem stems from weak sphincter muscles, impaired nerve reflexes, reduced rectal sensation, or some combination. This matters because treatment differs significantly depending on the underlying issue. Anorectal manometry is also used to evaluate Hirschsprung’s disease, a condition present from birth where nerve cells are missing from part of the bowel. Large or recurring hemorrhoids and chronic anal fissures can sometimes signal an underlying coordination disorder that manometry can identify.
How to Prepare
Your rectum and anal canal need to be empty for accurate results. You’ll be asked to avoid eating before the test and to use an enema at home beforehand. Your provider will give you specific timing and product recommendations. If stool is still detected during a rectal exam at the appointment, an additional enema may be given, with at least 30 minutes of wait time before the test begins.
What Happens During the Test
You’ll lie on your left side with your knees and hips bent at about 90 degrees. A thin, lubricated catheter is gently inserted into the rectum. Once it’s in place, the probe stays stationary for the entire study. There’s a five-minute rest period at the start so your muscles can return to their natural resting state.
From there, the test moves through a series of brief maneuvers:
- Resting pressure. The probe records your baseline sphincter tone over about 20 seconds, with no effort required from you.
- Squeeze. You’re asked to squeeze your anus as tightly and as long as you can, up to 30 seconds. This is repeated three times with a one-minute rest between each attempt.
- Cough reflex. You cough or blow against resistance while the probe checks whether your outer sphincter contracts automatically. This tests a specific spinal nerve reflex.
- Simulated evacuation. You bear down as if having a bowel movement. This is done once without and once with a small balloon inflated in the rectum, to see how your muscles coordinate during pushing.
- Sensation testing. A balloon at the tip of the catheter is gradually inflated to measure when you first feel it and the maximum volume you can tolerate. Each inflation is held for at least 30 seconds.
- Balloon expulsion. A small balloon is inflated in the rectum and you’re asked to push it out. This is a practical screening test for coordination problems during defecation.
The entire procedure typically takes 15 to 30 minutes. No sedation is needed, and complications are rare. The main precaution is letting your technician know if you have a latex allergy.
What the Test Measures
Anorectal manometry captures several distinct measurements, each pointing to a different aspect of how your rectum and sphincter muscles function.
Resting pressure reflects how well your internal sphincter (the muscle you don’t consciously control) maintains its tone. Normal resting pressure ranges from about 40 to 70 mmHg on conventional systems, though newer high-resolution equipment may record slightly different ranges. Squeeze pressure reflects voluntary external sphincter strength. Normal squeeze pressures range from 100 to 180 mmHg on conventional systems, with high-resolution readings showing wider variation, especially in men (up to 328 mmHg).
Rectal sensation is measured by the volume of air needed to trigger your first awareness of the balloon (typically 10 to 40 ml) and the maximum volume you can comfortably tolerate (100 to 300 ml on conventional testing). Values outside these ranges can indicate either heightened sensitivity or reduced sensation, both of which affect bowel function.
One particularly important reflex the test checks is whether the internal sphincter relaxes when the rectum stretches. This automatic relaxation is a normal part of how your body signals the urge to have a bowel movement. Its complete absence can suggest Hirschsprung’s disease.
How Results Are Interpreted
Results are categorized using a standardized system called the London Classification, which organizes findings into four main areas: reflex function, muscle tone and strength, coordination during pushing, and rectal sensation. Within each area, your results are graded as major findings, minor findings, or inconclusive.
Major findings that typically lead to a clear diagnosis include absent reflexes (which raises concern for Hirschsprung’s disease) and low sphincter tone with normal squeeze strength, which points to internal sphincter dysfunction. Minor findings include elevated resting pressure, which can contribute to conditions like anal fissures, and coordination patterns where pushing produces inadequate force.
Coordination problems during simulated evacuation are especially common in people with chronic constipation. The test can reveal dyssynergia, where the sphincter muscles paradoxically tighten when they should relax during pushing. It can also identify poor propulsive force, where the rectum doesn’t generate enough pressure to move stool forward, or a combination of both. These distinctions matter because pelvic floor physical therapy, specifically biofeedback retraining, can be highly effective for coordination disorders but wouldn’t help someone whose problem is purely slow transit.
Conventional vs. High-Resolution Manometry
Older conventional catheters use a handful of sensors spaced along the probe. Newer high-resolution systems pack many more sensors along the full length of the anal canal, measuring pressure in a continuous, circumferential pattern. The result is a detailed color-coded pressure map rather than individual point readings. Some systems add a third dimension, creating a 360-degree picture of how pressure distributes around the canal.
In practice, this means high-resolution manometry can detect asymmetric weakness or localized sphincter defects that conventional systems might miss. Reference ranges differ between the two technologies, so your results are always compared against norms specific to the equipment used.
After the Test
There’s no recovery period. The catheter is removed and you can return to your normal activities, including eating, right away. You won’t need anyone to drive you home, since no sedation is involved. Some people feel slight rectal fullness or mild discomfort during the balloon portions of the test, but this resolves immediately once the probe is removed. Results are typically reviewed by a gastroenterologist or colorectal specialist and discussed at a follow-up appointment, where the findings guide next steps for treatment or further testing.