PRO-2 Score in Ulcerative Colitis: What It Means

PRO-2 is a two-item score. You rate how many stools you are passing compared with your own normal, from 0 to 3, and you rate how much blood you are seeing, from 0 to 3. Add them together and you get a number between 0 and 6. That is the whole instrument.

It looks trivially simple, and that is exactly why it confuses people. A score with only two items and sixteen possible states is now used to decide whether a drug worked in a trial costing hundreds of millions, to decide whether you are "in remission" at a clinic visit, and increasingly to check in on you between appointments. This guide covers what each item is really asking, what the number can and cannot tell you about the inside of your colon, the four different things people call "the Mayo score", and how to read your own PRO-2 without either ignoring it or trusting it more than it deserves.

What the PRO-2 score is, and what each number means

PRO-2 combines two of the four components of the Mayo Clinic Score, the ones you report yourself rather than the ones a clinician or an endoscope supplies (Jairath 2015). Rectal bleeding, stool frequency and the Mayo endoscopic subscore are separate components of that parent score (Colombel 2017).

Here is exactly how each item is scored, as used in a study that recorded both items on three consecutive days in the week before colonoscopy (Dragasevic 2020):

Add the two and you have your PRO-2. Nothing is weighted, nothing is adjusted for how ill you feel, and there is no room for anything else.

That design has two consequences worth sitting with. First, there are only sixteen possible combinations, so the score is coarse. A single point is a large proportional move on a six-point scale, which is why a one-point change can flip you across a trial's remission line. Second, both items are scored relative to something: your own normal for stools, and a rough frequency judgement for blood. Neither is an absolute count.

Why a two-item score exists at all

PRO-2 exists because of a regulatory problem, not a clinical one. Drug regulators wanted a patient-reported endpoint for ulcerative colitis trials, and at the time there was not one.

The Mayo Clinic Score itself dates to a 1987 randomised trial of coated 5-aminosalicylic acid in 87 people with mildly to moderately active ulcerative colitis, which monitored outcomes through proctosigmoidoscopy, physicians' assessments and patients' own daily symptom records (Schroeder 1987). That combination of a scope reading, a clinician judgement and patient-reported symptoms became the standard activity measure for the next three decades.

The problem is that two of those components are not patient-reported. The US Food and Drug Administration issued formal guidance on the role of patient-reported outcome instruments in supporting product labelling claims, and as the authors of the PRO-2 paper put it, "no validated PRO exists for ulcerative colitis" (Jairath 2015). So rather than wait years for one to be built from scratch, they asked whether the patient-reported items already inside the Mayo score could be pulled out and used on their own.

Using data from a mesalazine induction trial and validating against a phase 2 trial of an anti-integrin antibody, they found that a two-item PRO consisting of rectal bleeding = 0 and stool frequency ≤ 1 or ≤ 2, combined with an endoscopy subscore of ≤ 1, produced statistically significant separation between drug and placebo with effect sizes and placebo rates most similar to the original trials. Crucially, when the patient-reported items were used alone, placebo remission rates were high (Jairath 2015).

Read that last point again, because it is the single most useful thing to know about PRO-2. Its own developers found that symptoms on their own were too easy to improve without an active drug, and recommended pairing them with endoscopy as a co-primary endpoint. Their conclusion described PRO-2 as something that "may be an appropriate interim outcome measure". The word interim is in the title of the paper.

The four different numbers people call "the Mayo score"

A large share of the confusion around PRO-2 is not about PRO-2 at all. It is that at least four different numbers get referred to casually as "your Mayo score", and they are on different scales with different meanings.

This matters in practice. In a thread on r/UlcerativeColitis, someone described a consultation in which they were told their "Mayo Clinic score is 1" and that, therefore, none of the gut symptoms they had experienced since diagnosis could be attributed to their ulcerative colitis. Another person replying to the same thread described being told something similar after a sigmoidoscopy scored Mayo 1 (r/UlcerativeColitis thread). In both cases the number being quoted was almost certainly the endoscopic subscore, which is about what the lining looks like, not a PRO-2 and not the full score.

That distinction changes the conversation entirely. An endoscopic subscore of 1 means mild visible changes in the lining. It does not mean the patient's symptoms are imaginary, and it does not on its own resolve what should happen next. Whether a particular treatment is right for you is a decision for you and your IBD team with your full clinical picture in front of them, not something a single subscore settles. If you are ever quoted a number you do not recognise, the useful question is simply: which score is that, and what is its range?

"Normal for you" is doing a lot of work in that first item

The stool frequency item is not a count. It is a count relative to your personal baseline, and that baseline is rarely written down anywhere.

Scoring 0 requires knowing your normal number of stools. For someone diagnosed at twenty who has been symptomatic on and off since, "normal" may be a memory from a decade ago, or a guess, or the best stretch they have had recently. Two people with identical bowel habits today can score 0 and 2 purely because they anchored to different baselines. And an anchor tends to drift: if you have been going four times a day for a year, four times a day starts to feel like your normal.

This is the single biggest source of noise in a self-scored PRO-2, and it is fixable. Write down what your stool count looks like during your best stretch, date it, and use that as the reference every time. Our guide to knowing whether your ulcerative colitis is flaring goes into how to establish and hold a personal baseline, and covers the SCCAI, a longer self-scored index that adds urgency and general well-being to the same two symptoms.

There is a second, less obvious problem with the item. Stool frequency in ulcerative colitis is not driven only by inflammation. After years of disease, or after surgery, the bowel's capacity can be permanently changed. The authors of one cohort study concluded that non-inflammatory changes, such as bowel damage, may contribute to raised stool frequency even after the lining has healed (Colombel 2017). A stool frequency subscore of 1 that never comes down may be telling you something true and permanent about your anatomy rather than something alarming about your inflammation.

The rectal bleeding item is the sharper of the two

If you only look at one half of your PRO-2, look at the bleeding item. Across the evidence base, it is consistently the better signal.

In the 103-person EMBARK cohort, identifying people with inactive disease using symptom subscores gave the following results against an endoscopic subscore of 0 or 1: rectal bleeding, 77% sensitivity and 81% specificity; stool frequency, 62% and 95%; both combined, 54% and 95%. Against the stricter target of an endoscopic subscore of exactly 0, rectal bleeding reached 87% sensitivity and 66% specificity (Colombel 2017). Note that several of the authors of that paper were employees of Genentech, which funds work in this area.

A systematic review of 23 studies covering 3,320 people with ulcerative colitis reached the same conclusion from a different angle: composite clinical measures including rectal bleeding and stool frequency correlated moderately to strongly with endoscopic activity, and the absence of rectal bleeding identified people with inactive disease more sensitively than normalisation of stool frequency did. Symptoms also correlated more strongly with endoscopic activity in left-sided colitis than in extensive colitis (Restellini 2019). A 2025 systematic review of patient-reported measures, funded by Galapagos NV, likewise found that rectal bleeding subscores showed noticeably higher accuracy than stool frequency across the studies it reviewed (Calvet 2025).

One caution about the bleeding item that the score cannot handle: it does not ask where the blood is coming from. Haemorrhoids, anal fissures and other non-colitis causes all produce visible blood. That is a question for your clinician, and the score simply records what you saw. Either way, new or increasing rectal bleeding is a reason to contact your IBD team promptly rather than to adjust a number and move on.

What a PRO-2 of 0 does and does not prove

A PRO-2 of 0 is a genuinely good sign, and it is not proof that your colon has healed. The gap between those two statements is where most of the disappointment around this score lives.

The clearest numbers come from a pooled analysis of the ULTRA 1 and ULTRA 2 phase 3 adalimumab trials, funded by AbbVie, with several authors employed by the company (Jharap 2015). At week 8:

• A rectal bleeding subscore of 0 predicted an endoscopic subscore of 0 or 1 in 69% of patients.
• A stool frequency subscore of 0 predicted it in 84%.
• Both subscores at 0 predicted it in 90%.

But against the stricter target of a completely normal-looking lining (endoscopic subscore of exactly 0), those same figures fell to 26%, 37% and 46%. And looking from the other direction: among people whose lining was completely normal at week 8, 87% reported no rectal bleeding but only 29% reported normal stool frequency. By week 52 that had only risen to 41%.

So a fully normal stool frequency is the exception even when the colon looks perfect. If your stool frequency subscore sits at 1 indefinitely while your bleeding item stays at 0, you are in the majority, not the minority.

A prospective study of 171 people with ulcerative colitis referred for endoscopy compared PRO-2 remission (rectal bleeding 0 and stool frequency ≤ 1) with the partial Mayo score and the SCCAI against three different endoscopic indices. All performed similarly, with areas under the curve from 0.72 to 0.93, and the authors found no clinically meaningful difference in accuracy between the scores or the definitions. In the same study, agreement between C-reactive protein and clinical or endoscopic remission was poor, while agreement between faecal calprotectin and either the bleeding subscore, PRO-2 or the endoscopic indices was moderate to strong (Golovics 2022).

There is one outlying result worth naming honestly. A cross-sectional study of 96 newly diagnosed people with ulcerative colitis found a strong correlation between PRO-2 and endoscopic activity, with a Spearman coefficient of 0.84 (Dragasevic 2020). That is much higher than most studies report, and the likely reason is the population: newly diagnosed, untreated people span the full range from quiet to severe, which inflates correlations. In the broader review, correlations between patient-reported measures and the Mayo endoscopic subscore ranged from 0.34 to 0.84, and the reviewers concluded that such measures "cannot replace objective measures of IBD activity" (Calvet 2025).

Both the American College of Gastroenterology guideline for ulcerative colitis in adults and the ECCO therapeutics guideline are built around combining symptoms with objective assessment rather than relying on either alone (Rubin 2019; Raine 2022). PRO-2 is one input among several.

The remission threshold is not one number

If you have seen PRO-2 remission defined three different ways, you have not misread anything. There genuinely are multiple definitions in active use.

The original paper tested rectal bleeding = 0 with stool frequency ≤ 1 or ≤ 2, and also looked at a total PRO-2 of 0 (Jairath 2015). Later work uses rectal bleeding = 0 plus stool frequency ≤ 1 (Golovics 2022). Some analyses report a total of 0 to 1 as remission.

This is a symptom of a wider problem. A systematic review of 83 placebo-controlled randomised trials in ulcerative colitis, covering 17,737 patients, found more than 50 different definitions of response or remission, with substantial variation in how clinical and composite endpoints were built (Ma 2018). The 2026 review of patient-reported measures across 132 IBD trials reached the same verdict: outcome definitions and reporting formats were highly heterogeneous, only a minority of instruments had been extensively validated, and none of those that had were developed following regulatory recommendations (Hanzel 2026).

An earlier systematic review of how patient-reported instruments in IBD were actually built found the body of evidence for content validity to be limited, with most evidence of low or very low quality, and recommended that future development studies should involve patients (van Andel 2020). PRO-2 was assembled from items that already existed in a physician-designed index, rather than built from interviews with people who have ulcerative colitis about what matters to them. That history explains a lot about what it leaves out.

The practical upshot: when you read that a drug achieved "clinical remission" in some percentage of patients, the number is only interpretable alongside the definition used in that specific trial. And when someone tells you that you are "in PRO-2 remission", it is a fair question to ask which threshold they are applying.

What PRO-2 leaves out, and why it matters more than you think

PRO-2 measures two symptoms. Ulcerative colitis produces considerably more than two, and the omissions are not minor.

Urgency. The sudden, immediate need to get to a toilet is, for many people, the symptom that dictates whether they can take a train, sit in a meeting or leave the house. It is not in PRO-2. An Urgency Numeric Rating Scale was developed from qualitative interviews with people who have ulcerative colitis and validated separately, asking for the worst urgency over the past 24 hours on a 0 to 10 scale (Dubinsky 2022a). In a psychometric evaluation across 1,162 phase 3 trial participants, it showed strong test-retest reliability, an improvement of 3 or more points represented meaningful change, and a score of 1 or less marked a urgency remission threshold associated with clinical, endoscopic and histological remission. Notably, correlations with the modified Mayo rectal bleeding item were only weak to moderate, meaning urgency carries information the bleeding item does not (Dubinsky 2022b). Both papers were authored substantially by Eli Lilly employees, the manufacturer of a drug whose trials used the instrument.

Abdominal pain, fatigue and night-time stools. None of these appear in PRO-2 either. Fatigue is among the most commonly reported problems in IBD: a meta-analysis of 20 studies put pooled prevalence at 47%, rising to 72% in active disease and remaining at 47% in remission, with sleep disturbance, anxiety, depression and anaemia as the most commonly reported associated factors (D'Silva 2022). A score of 0 on PRO-2 is entirely compatible with being exhausted.

The field has started to correct for this. The mirikizumab phase 3 programme included improvement in bowel-movement urgency among its major secondary endpoints (D'Haens 2023), and a dedicated symptom-control analysis of the same programme tracked stool frequency, rectal bleeding, bowel urgency, abdominal pain and fatigue as separate strands, plus a "comprehensive symptom control" composite (Danese 2024). A further analysis found that urgency remission was associated with substantially higher rates of quality-of-life remission, and with improvements in fatigue, abdominal pain and nocturnal stool (Long 2024).

At guideline level, the STRIDE-II consensus of the International Organization for the Study of IBD set symptomatic relief and normalisation of serum and faecal markers as short-term targets, while confirming clinical remission and endoscopic healing as long-term targets and adding absence of disability and restoration of quality of life (Turner 2021). PRO-2 speaks to the first of those and is silent on the rest.

A worked example: two people, both scoring 2

The clearest way to see why the total is the least informative part of a PRO-2 is to look at two people who score the same.

Person A: stool frequency 2, rectal bleeding 0. Total: 2. Three to four more stools a day than their normal, no visible blood at all. They were diagnosed eleven years ago and have had two significant flares. Their last calprotectin was 38 µg/g, their last scope was clean. The bleeding item, the better predictor of a quiet lining, is at its best possible value. Their raised stool count may be the durable, non-inflammatory change in bowel capacity that shows up in the cohort data, or overlapping IBS-type symptoms, which affect roughly a quarter to a third of people with IBD in remission (Fairbrass 2020; Colombel 2017). This is a conversation about symptom management and, possibly, a dietitian referral.

Person B: stool frequency 0, rectal bleeding 2. Total: 2. Their stool count is entirely normal, but there is obvious blood with the stool most of the time, and it started three weeks ago. Same total, completely different situation. Visible blood most of the time points towards inflamed or ulcerated lining, and it is the item that most reliably tracks endoscopic activity (Restellini 2019). This warrants contacting the IBD team promptly.

The number 2 told you nothing useful in either case. The pair of numbers told you almost everything. Whenever you record or report a PRO-2, record both items separately and keep the total as an afterthought.

Scoring yourself is not quite the same measurement

Trials do not collect PRO-2 the way most clinic visits do, and the difference is larger than it sounds.

In research use, both items are recorded in a daily diary and then averaged, typically over about three consecutive days (Dragasevic 2020). What usually happens in a clinic is that someone asks you how things have been, and you reconstruct an average from memory across weeks. Those are different instruments wearing the same name.

The classic demonstration of why daily entry matters came from a chronic pain study that secretly instrumented paper diaries to record when the binder was actually opened. Participants submitted diary cards corresponding to 90% of assigned times, but electronic records showed actual compliance was 11%. On 32% of study days the binder was never opened, yet reported compliance for those days still exceeded 90%. With an electronic diary that timestamped entries, actual compliance was 94% (Stone 2003). That study was not in IBD, and pain is not stool frequency, but it is the reason regulators favour timestamped daily capture over retrospective recall.

Practically, this means three things if you want your own PRO-2 to be worth anything:

1. Record on the day, not at the end of the week and certainly not in the waiting room.
2. Score against a written baseline, not against a remembered one.
3. Label it as a self-score when you hand it over, so nobody mistakes it for a clinician-administered measurement.

If you are choosing a way to capture this, our comparison of apps for tracking ulcerative colitis walks through what a UC tracker actually needs to capture and why most tracking habits fade within three weeks. Clairop records both PRO-2 items alongside urgency, pain and medication, and turns them into a single-page report you can take to an appointment; you can see how that works on the how it works page.

PRO-2 is quietly moving out of trials and into clinic visits

The reason this keyword is being searched at all is that PRO-2 is escaping the trial setting.

An international multi-stakeholder consensus involving 136 participants, including 45 patient advocates, 74 clinicians and researchers, 13 industry representatives and four regulators across 20 countries, defined a core outcome set for IBD. It recommended PRO-2 and the IBD-Control questionnaire to collect disease-specific patient-reported outcomes at every contact with an IBD practitioner, with generic measures collected annually (Fierens 2024). Implementation is starting in Vienna, Berlin, Barcelona, Leuven and Rotterdam.

That is a meaningful shift. It also raises the stakes on understanding what the score is, because you are increasingly likely to be asked for it, to see it in a portal, or to be told a decision rests partly on it.

It is worth keeping expectations calibrated about what remote score collection achieves on its own. A Cochrane review of 19 randomised trials covering 3,489 people found that web-based disease monitoring was probably equivalent to usual care for disease activity, for the occurrence of flares or relapses, and for quality of life, all on moderate-certainty evidence, with a small probable improvement in medication adherence in one study (Gordon 2023). Collecting a number more often is not, by itself, treatment. What it can do is replace "it's been bad for a while" with a dated series.

Nor is PRO-2 the only, or necessarily the best, non-invasive index. A prospective comparison of all the non-invasive activity indices available at the time, in 86 adults with ulcerative colitis, concluded that the Walmsley index (the SCCAI) and the paediatric PUCAI performed best across validity, reliability and responsiveness, with the partial Mayo score performing well on three of the four properties tested (Turner 2009). PRO-2's advantage is brevity and its match to how trials report results, not superior measurement.

How to use your own PRO-2 without over-reading it

A few habits turn this score from a source of anxiety into something useful.

Track the two items separately, always. The total obscures the only distinction that reliably matters. A move from 1 to 2 driven by bleeding is a different event from the same move driven by stool count.

Treat one reading as noise and the trend as signal. A single bad day moves a six-point score considerably. Three weeks of daily entries showing bleeding climbing from 0 to 1 to 2 is information. Tuesday's score is not.

Pair it with an objective test rather than substituting for one. Faecal calprotectin showed moderate to strong agreement with both the bleeding item and endoscopic indices, while C-reactive protein agreed poorly (Golovics 2022). Our guide on knowing whether your ulcerative colitis is flaring covers calprotectin thresholds and day-to-day variation in detail.

Record the things PRO-2 ignores alongside it. Urgency on a simple 0 to 10 scale, whether you were woken at night, abdominal pain, fatigue, and whether you took your maintenance treatment. These are the items that change the picture, and several of them now have validated instruments of their own (Dubinsky 2022a).

Agree a trigger in advance. Ask your IBD team, at a calm appointment, what change in your numbers should prompt a call rather than a wait. A score that leads nowhere is a score not worth keeping.

Do not use it to make treatment decisions on your own. PRO-2 was built to compare groups of patients in trials. It was never designed to tell an individual whether a medication is working, and no score should be the basis for starting, stopping or changing anything. That conversation belongs with your IBD team.

Myths about the PRO-2 score

"PRO-2 of 0 means I'm in remission." It means you are in symptomatic remission on two symptoms. Among people whose lining looked completely normal, fewer than half had both subscores at 0 at week 8 (Jharap 2015), and conversely a low score does not rule out ongoing inflammation. Symptomatic, endoscopic and histological remission are different things, and STRIDE-II treats them as separate targets (Turner 2021).

"The higher the total, the more inflamed I am." Only loosely. Correlations between patient-reported measures and the Mayo endoscopic subscore ranged from 0.34 to 0.84 across studies, and the two items behave differently, with bleeding consistently the more accurate (Calvet 2025).

"PRO-2 replaces colonoscopy." No guideline says this and no study supports it. The developers themselves recommended pairing PRO-2 with endoscopy as a co-primary endpoint precisely because symptoms alone produced high placebo response (Jairath 2015), and the most recent systematic review concluded that patient-reported measures cannot replace objective measures of activity (Calvet 2025).

"My stool frequency subscore should reach 0 if treatment is working." For most people it will not, even with a healed colon. Only 29% of people with a completely normal lining reported normal stool frequency at week 8, rising to 41% at week 52 (Jharap 2015).

"PRO-2 is a validated patient-reported outcome measure." It is a pragmatic extract from an older physician-designed index, explicitly described as interim by its developers (Jairath 2015). A 2026 review of patient-reported measures in IBD trials found that of the minority of instruments that had undergone extensive validation, none were developed following regulatory recommendations (Hanzel 2026).

"A normal PRO-2 means my symptoms are IBS, not colitis." It means these two symptoms are quiet. IBS-type symptoms are genuinely common in IBD remission, at around 28.7% in ulcerative colitis (Fairbrass 2020), but attributing symptoms to one cause or another is a clinical judgement made with tests, not an inference from a two-item score. Someone in r/UlcerativeColitis described a colonoscopy showing a Mayo endoscopic score of 0 while still getting intermittent diarrhoea and a lot of wind, which is exactly the situation where this question arises (r/UlcerativeColitis thread).

When to contact your IBD team

Scores are for tracking, not for triage. Some things warrant a call regardless of what any number says.

Contact your IBD team promptly if you develop or notice:

• New rectal bleeding, or bleeding that is increasing
• Passing blood alone, without stool
• Being woken at night by the need to open your bowels
• Fever, or feeling generally unwell alongside gut symptoms
• Severe or persistent abdominal pain
• Unexplained weight loss
• Symptoms of anaemia such as breathlessness or unusual tiredness with pallor
• Six or more bloody stools a day, or any sudden, severe worsening

Seek urgent medical attention for severe abdominal pain with a distended abdomen, a high fever, persistent vomiting, or an inability to keep fluids down. These can indicate complications that need assessment the same day.

Also worth a conversation, though not urgently: urgency or incontinence that is restricting your life, fatigue that is not improving, and any symptom that matters to you but does not show up anywhere in PRO-2. Given that clinicians were unaware of urgency in over half of the people reporting it in one survey (Wang 2024), saying it out loud is often the only way it enters the record.

The honest bottom line

PRO-2 is a useful, extremely short score that captures two real and important symptoms. It is not a measure of inflammation, it is not a validated instrument in the way the term is usually meant, and it was assembled as a stopgap that has outlived the gap it was meant to fill.

Read it as two numbers rather than one. Weight the bleeding item more heavily than the stool frequency item. Expect stool frequency to stay slightly raised even when everything else is quiet. Record the symptoms it ignores alongside it. Pair it with calprotectin and with the judgement of your IBD team, and treat it as one line in a longer story rather than a verdict.

If you want to go deeper on the related questions, our guides on knowing whether your ulcerative colitis is flaring and whether food can trigger a UC flare pick up where this one stops.