Functional Constipation: Types and Diagnosis
Functional Constipation: Types and Diagnosis

Functional Constipation: Types and Diagnosis

Oof this is a big topic! So right off the bat, let's narrow our scope. And, if you missed my first article about talk (the basics of bowel function), you can check that out here.

By, Stephanie Dillon, PT, DPT, WCS

This post will be about functional constipation. What do I mean by that? Basically this means there are no other medical explanations for your constipation. No IBS, Crohn's or Celiac, or really serious pathologies like cancer, etc. So before we dive in, let's review some major symptoms that would require you to contact your doctor ASAP to get some more serious diseases ruled out:

  • Blood in the stool

  • A sudden change in bowel habits (especially after the age of 50 years)

  • Anemia

  • Unexplained weight loss

  • Any bowel changes if you have a family history of colon cancer

How do I know if I have functional constipation?

For starters, your symptoms must be present for 6 months or more, and also you must have had some symptoms in the last 3 months. Then, you also need 2 or more of these:

  • Straining for more than 25% of bowel movements (BMs)

  • Lumpy or hard stools for more than 25% of BMs (refer back to my last article for the Bristol stool scale—these would generally be types 1-2)

  • Sensation of incomplete emptying at least 25% of the time

  • Fewer than 3 spontaneous BMs/week (spontaneous meaning without the use of laxatives or other agents to produce a BM)

  • A sensation of something blocking your rectum/anus for at least 25% of BMs

  • Needing to "splint" your perineum (press a finger upwards against the tissue between your vagina and anus to help facilitate defection) or needing to put your finger in your rectum to help guide stool out for more than 25% of BMs (yes some people have to do this!)

  • Loose stools rarely present without the use of laxatives

  • Insufficient symptoms to diagnose IBS-constipation 

Are there different types of functional constipation?

Yes! Functional constipation generally falls into two categories:

  1. Slow transit constipation. Essentially this means that your intestines are not moving your waste along quickly enough through your colon. Symptoms include reduction in the urge to defecate, abdominal pain, and abdominal distension/bloating. This leads to hardened stool, as water from stool is lost as it moves through the colon. This hardened stool is slower to reach your rectum, and thus requires greater force to evacuate.  

  2. Defecation disorders. Sometimes called obstructed defecation, outlet dysfunction, or even a non-relaxing puborectalis, this essentially means you have lost the coordination/strength between your abdominals and pelvic floor  that is needed to evacuate your stool. Generally you will experience a long toileting time to produce a bowel movement, a lot of straining, and sometimes the need to use manual assistance to empty the rectum.

Generally the big differentiator here is that with slow transit constipation, you feel like your stool is just sitting in your belly and not even making it to your rectum (you know you should go, but can go a long time without the urge to go). With defecation disorders, you know the stool is in your rectum and you have the urge to defecate, but you can't get it out.

And of course for some people, there can be a mix of these two things occurring at the same time.

How do I know if my constipation is slow transit or a defecation disorder (or both)?

Basically, there are a series of typically not-so-fun tests you can undergo. Typically these tests are ordered by a gastroenterologist or a colorectal surgeon (or a nurse practitioner or physician assistant in one of those offices), so you will need a referral to a specialist before having any of these tests.  I'll give you a brief rundown of the options here.

For slow transit constipation:

This is the easiest/least-invasive test, commonly known as a Sitz-marker study. Basically it requires you to swallow a capsule containing 24 radiopaque markers. Then, via a series of abdominal x-rays, your doctor can tell how long it takes for those markers to move through your colon. Based on the method they prefer, they may ask you to:

  • Take one capsule, then have an abdominal x-ray 5 days later. The goal is to have less than 5 markers remaining in your colon.

  • Take one capsule on day 1, one on day 2, and then another on day 3. Then abdominal x-rays are taken on days 4 and 7.  If you have more than a total of 68 markers left (out of the original 72) between the tests on both days, then you earn the diagnosis of slow transit constipation.

There are also newer tests in the works, like a wireless pH-pressure capsule you can take, but that requires some fancier monitoring equipment and I don't believe is used regularly yet.

For defecation disorders:

These tests are significantly more invasive and less fun than for slow transit. I'll outline them here, but also know in most states you can just make an appointment with a pelvic floor physical therapist (PT) who can also diagnose the same thing with an intra-rectal exam. A rectal exam is also not super fun, but when you read the rest of these you may want to take that option.

  • Rectal Balloon Expulsion Test: Basically you sit on a toilet-like object, have a balloon inserted into your rectum that is then filled with water, and finally you try to poop it out. If it takes you longer than one minute to expel the balloon, then you earn the diagnosis of a defecation disorder. HOWEVER, this test is not valid for anyone with prolapse or pelvic floor laxity.

  • Anorectal Manometry: This test is a measure of the pressure inside the rectum and anus, both at rest and when you use your pelvic floor muscles. It can also test your ability to sense when your rectum is full. Essentially you lay on your left side, have a catheter inserted into your rectum, and then that catheter is pumped with air. It can measure the pressure at various points along the rectum, and then also can measure what happens when you squeeze your muscles or try to bear down as if having a BM. For more details, check out this article.  Many times this test is done at the same visit as the rectal balloon expulsion test.

  • Defecography: This test is generally done only if the anorectal manometry test results don't match up with your symptoms, or if your doctor suspects you have a large rectocele. This is a visual test to actually see what happens in your rectum when you try to poop. So as a result, it requires either a fluoroscopic x-ray or an MRI. Basically your rectum is filled with a barium paste (similar to the consistency of poop) so that the radiology technician can see the paste as you bear down to eliminate it. Then, you sit on a "special toilet" inside a specialized MRI or x-ray machine. You will try to eliminate the barium paste while a series of pictures is taken of your insides as you do so.  For more of the lovely details, click here.  

So, remember what I said about a rectal exam from a pelvic floor PT (1:1 in a private room) being possibly preferable to these types of tests (definitely not 1:1, and now you are trying to poop on command in front of strangers 😬)??  Yeah...I'd take the PT exam any day!

What's the first step in treating functional constipation?

Generally, the basics you already know. If you tell your doctor you are constipated, they will generally tell you to increase water and fiber, and may recommend short-term use of laxatives (again, see my first article for fiber and water basics). However, this guidance will fail in about 50% of people. But on the other hand, then it means just basic info can help 50% succeed! The problem is that while constipation may be dietary-related for a lot of people, it doesn't get to the root cause of the constipation for many others. So, make sure your fiber and water intake are good first, and if that doesn't help, move on to some other treatments.

Also, long-term use of stimulant laxatives is NOT recommended (see this article for a full breakdown on types of laxatives). This is because then your body gets really used to relying upon the laxative to push your stool through your colon, rather than the colon doing the work itself.  Stimulant laxatives are typically things like Ducolax and senna. Other types of laxatives, such as osmotic laxatives (lactulose, Miralax) and stool-softening laxatives (Colace, aka ducosate) do not have the same problems and are safe for long-term use. However, it is well-known that Colace is no better than placebo, so honestly, don't even bother in my opinion! And of course, with my PT hat on I'd rather have you get to the bottom of your constipation rather than just relying upon laxatives anyway.

If I'm already good on fiber and water, what's next?

I know this question probably applies to a lot of you! However, the answer to this is SO big that I needed to save it for another article. So, click here to read about treatment options for functional constipation.


Bharucha, A. E., & Wald, A. (2019). Chronic Constipation. Mayo Clinic proceedings, 94(11), 2340–2357. (the 2 last images come from this article as well!)

LaCross, Jennifer A. PT, DPT, PhD(c)1; Borello-France, Diane PT, PhD2; Marchetti, Gregory F. PT, PhD2; Turner, Rose MLIS3; George, Susan PT, DPT4. Physical Therapy Management of Functional Constipation in Adults Executive Summary: A 2021 Evidence-Based Clinical Practice Guideline From the American Physical Therapy Association's Academy of Pelvic Health Physical Therapy. Journal of Women's Health Physical Therapy 46(3):p 147-153, July/September 2022. | DOI: 10.1097/JWH.0000000000000245

Photo by Andrea Piacquadio: