About the Boston Bowel Preparation Scale (BBPS)
Scored on withdrawal, after all washing and suctioning is finished — not on the first view going in. Each of three segments (right, transverse, left) is graded 0 to 3, giving a total from 0 to 9. A preparation counts as adequate when the total is 6 or more and no single segment scores below 2, and both halves of that rule are load-bearing: a total of 6 made up of 3 + 3 + 0 is not adequate, because a well-seen segment cannot compensate for one you never saw. In the derivation study, scores of 5 or more were associated with a polyp detection rate of 40% against 24% below that.
Formula
BBPS = right + transverse + left Adequate = (BBPS ≥ 6) AND (lowest segment ≥ 2)- 0
- Unprepared segment — mucosa not seen because of solid stool that cannot be cleared.
- 1
- Portion of the mucosa seen, but other areas of the segment obscured by staining, residual stool or opaque fluid.
- 2
- Minor residual staining, small fragments of stool or opaque fluid, but the mucosa of the segment is seen well. This is the minimum acceptable per-segment score.
- 3
- Entire mucosa of the segment seen well, with no residual staining, fragments or opaque fluid.
- Score after washing and suctioning, on withdrawal. Scoring the initial view measures the purgative rather than the examination, and produces systematically lower numbers.
- The adequacy rule is a conjunction. A total of 6 with a segment scoring 0 or 1 is an inadequate preparation, and this is the single most common misreading of the scale.
- Nine is the maximum, not ten. The original paper describes it as a 10-point scale because it counts the possible values 0 through 9, which has caused persistent confusion about the ceiling.
- There is no segment weighting. A poorly prepared right colon and a poorly prepared rectum cost the same points, even though their clinical consequences differ substantially.
- If the caecum was not reached, the right colon cannot be scored and the examination is incomplete on separate grounds — BBPS assumes a complete colonoscopy.
Interpreting the result
An adequate preparation — 6 or more with no segment below 2 — supports applying standard surveillance and screening intervals, and that is the whole practical point of scoring it. An inadequate preparation means the examination did not achieve diagnostic quality, and the guidance is to repeat rather than to apply the interval that the findings would otherwise suggest; most guidelines advise repeating within a year, and sooner where the prior probability of neoplasia is high. Read a total of 6 with suspicion until you have checked the lowest segment. Beyond the binary, the gradient matters: mean BBPS in the derivation cohort of 633 screening colonoscopies was 6.0, and scores of 5 or more were associated with a polyp detection rate of 40% against 24% below that — so higher is better even within the adequate range, and a 6 is not equivalent to a 9. Where the preparation was inadequate, the reason is worth recording as well as the score, because a regimen problem, a timing problem and a motility problem call for different fixes at the repeat.
| Score | Band | What it means | Action |
|---|---|---|---|
| 7–9, all segments ≥ 2 | Good to excellent preparation | Mucosa well seen throughout. Highest confidence that significant pathology has not been missed | Apply standard screening or post-polypectomy intervals |
| 6, all segments ≥ 2 | Adequate preparation | Meets the accepted threshold for a diagnostic examination, but sits at its floor | Standard intervals apply. Record the segment scores so the next endoscopist knows where the margin was thin |
| ≥ 6 but any segment 0 or 1 | Inadequate despite the total | At least one segment was not adequately visualised; a well-prepared segment does not compensate for an unseen one | Treat as inadequate — repeat rather than applying standard surveillance intervals |
| < 6 | Inadequate preparation | Adenoma detection is reduced and the examination cannot be relied on to exclude significant pathology | Repeat, generally within one year and sooner if neoplasia is likely; review the preparation regimen before doing so |
What the Boston Bowel Prep Scale needs (3 inputs)
- Right colon (caecum and ascending colon)
- Graded 0 to 3. The segment where inadequate preparation matters most, because it is where flat and sessile serrated lesions concentrate and where they are hardest to see.
- Transverse colon (including hepatic and splenic flexures)
- Graded 0 to 3. The flexures belong to this segment by convention, which is worth knowing since residual fluid pools there.
- Left colon (descending, sigmoid and rectum)
- Graded 0 to 3. Usually the best-prepared segment, which is precisely why relying on a global impression formed distally is misleading.
What it returns
- BBPS total (0–9)
- The sum of the three segment scores. Quoted alone it is insufficient, because it does not reveal whether one segment scored 0.
- Lowest segment score
- Reported separately because the adequacy rule depends on it. This is the field that stops 3 + 3 + 0 being read as a pass.
- Adequate or inadequate
- Adequate requires a total of 6 or more AND every segment at 2 or more. Both conditions, not either.
How it is calculated
The scale was designed for colonoscopy outcomes research, which explains its two distinctive features. Existing scales had been built to compare oral purgatives against each other, so they were scored on the initial view and treated endoscopist washing as a confounder to be avoided; BBPS deliberately scores after all cleansing manoeuvres, because what determines whether a lesion is found is the view the endoscopist actually had. Second, it is segmental rather than global, because preparation quality is not uniform along the colon and a single number for the whole organ conceals exactly the failure that matters. Reliability was established by having 22 clinicians score video footage of colonoscopies on two separate occasions, then the scale was applied prospectively during screening colonoscopies to check that it tracked something clinically real rather than merely being reproducible.
Facts & figures
| Score | What you can see | Counts as adequate? |
|---|---|---|
| 0 | Mucosa not seen — solid stool that cannot be cleared | No |
| 1 | Part of the mucosa seen; other areas obscured by stool, staining or opaque fluid | No |
| 2 | Minor residual staining, small fragments or opaque fluid, but mucosa well seen | Yes — this is the minimum |
| 3 | Entire mucosa seen well; no residual staining, fragments or opaque fluid | Yes |
The line between 1 and 2 is the one that decides adequacy, and it turns on whether the mucosa of that segment was seen well rather than on how much material remained.
| Measure | Result |
|---|---|
| Inter-observer reliability (ICC) | 0.74, across 22 clinicians |
| Intra-observer reliability (weighted kappa) | 0.77 (95% CI 0.66–0.87), scoring the same footage on two occasions |
| Mean BBPS in 633 screening colonoscopies | 6.0 (SD 1.6) |
| Polyp detection rate, BBPS ≥ 5 versus < 5 | 40% versus 24% (P < .02) |
| Correlation with procedure times | Inversely correlated with insertion (r = −0.16, P < .003) and withdrawal (r = −0.23, P < .001) |
The polyp-detection association is what makes the scale more than a reproducible description — it links the number to the outcome colonoscopy exists to achieve. The study was single-centre, which its authors listed as its main limitation.
Evidence
Derivation — Boston, academic medical centre
2009 · n = 633Reliability assessed from colonoscopy video footage scored on two separate occasions by 22 clinicians, then the scale applied prospectively during screening colonoscopies and compared with polyp-detection rates and procedure times.
Inter-observer ICC 0.74; intra-observer weighted kappa 0.77 (95% CI 0.66–0.87). Mean BBPS 6.0 (SD 1.6). Scores of 5 or more were associated with a polyp-detection rate of 40% versus 24% below 5 (P < .02), and scores were inversely correlated with insertion (r = −0.16) and withdrawal (r = −0.23) times.
Comprehensive validation — Calderwood & Jacobson 2010
2010Follow-up study extending validation of the scale beyond the original derivation, examining its performance across a wider range of procedures and endoscopists.
Confirmed the reliability and construct validity of the segmental scoring approach, supporting its use as the standard measure of preparation quality in outcomes research.
Defining 'adequate' — Calderwood 2014
2014Study specifically addressing which BBPS values correspond to a preparation adequate for detecting neoplasia, in order to give the scale an interpretable threshold rather than only a range.
Established that a total of 6 or more with every segment scoring at least 2 provides a standardised definition of an adequate preparation — the rule now used in guidelines and quality reporting.
When to repeat — Clark 2014 meta-analysis
2014Systematic review and meta-analysis of adenoma miss rates by level of bowel preparation quality, addressing which preparations warrant early repeat colonoscopy.
Quantified the adenoma miss rate associated with poorer preparation and supported early repeat examination rather than application of standard surveillance intervals after an inadequate preparation.
Quantifying adequacy — Clark 2016
2016Cohort study in men undergoing screening or surveillance colonoscopy, examining how much preparation quality is needed before adenoma detection stops improving.
Supported the segment-level threshold, showing that detection continued to differ across the range conventionally described as adequate rather than plateauing at the cut-off.
How it compares
Boston Bowel Prep Scale vs Aronchick scale
Aronchick is a single global rating scored before cleansing; BBPS is segmental and scored after, which is why BBPS can identify the unseen segment that a global rating hides.
The Aronchick scale grades the whole colon on one categorical scale — excellent, good, fair, poor, inadequate — and was built for comparing purgatives, so it is applied to the view before the endoscopist washes. Two consequences follow. It cannot record that the right colon was unseen while the left was pristine, which is the specific failure that leads to missed proximal lesions; and its rating reflects the preparation the patient took rather than the examination the endoscopist achieved. BBPS was designed to correct both. Aronchick remains simpler and is still widely used descriptively, but it does not support a defensible adequacy threshold.
Boston Bowel Prep Scale vs Ottawa Bowel Preparation Scale
Both are segmental and validated; Ottawa also scores fluid volume separately, which makes it more granular but harder to apply consistently in routine practice.
The Ottawa scale grades three segments on a 0–4 cleanliness scale and adds a separate 0–2 score for the overall quantity of fluid, giving a 0–14 range. The extra fluid dimension is a genuine refinement, since pooled fluid obscures mucosa differently from adherent stool. In practice BBPS has become the more widely adopted instrument, largely because it has a single agreed adequacy definition — total 6 or more with all segments at 2 or more — that maps directly onto the decision about surveillance intervals. Ottawa is a reasonable choice for research where fluid burden is of interest; BBPS is the better fit where the output has to drive a clinical interval.
Boston Bowel Prep Scale vs Global 'prep quality' description in the report
A free-text rating cannot support an interval decision — 'fair preparation' is uninterpretable three years later, which is the problem BBPS exists to solve.
Descriptive terms are not standardised between endoscopists, are not segmental, and carry no threshold. The practical harm is downstream: an endoscopist reading a report that says 'prep fair, no polyps' cannot tell whether the caecum was visualised, so the negative examination gets treated as diagnostic and the interval is set accordingly. When a lesion appears before the next scheduled procedure it is classified as an interval cancer rather than as a missed lesion from a non-diagnostic examination. Recording three numbers and an adequacy verdict costs nothing and makes the interval decision auditable.
Pearls & pitfalls
- A total of 6 is not automatically adequate. Check the lowest segment — 3 + 3 + 0 sums to 6 and is an inadequate examination.
- Score on withdrawal, after washing and suctioning. Scoring the view on insertion measures the purgative, not the examination, and is the commonest procedural error.
- The maximum is 9, not 10. The original paper calls it a 10-point scale because it counts the ten possible totals from 0 to 9.
- The flexures belong to the transverse segment. Assigning the hepatic flexure to the right colon shifts scores between segments and can flip an adequacy decision.
- Segments are unweighted, but their consequences are not. An unseen right colon matters more than an unseen rectum, because that is where flat and sessile serrated lesions hide and where miss rates are highest.
- Record the three segment scores in the report, not just the total. The total alone loses the only information the next endoscopist needs.
- An adequate score is not a good score. Mean BBPS in the derivation cohort was 6.0, and polyp detection continued to differ across the adequate range — a 6 and a 9 are not equivalent examinations.
- BBPS presumes a complete colonoscopy. If the caecum was not intubated, the right colon has not been assessed and the examination is inadequate for a separate reason the score does not capture.
- An inadequate preparation is a reason to repeat, not a reason to lengthen the interval on the assumption that nothing was found.
Critical actions
- Score each segment after all washing and suctioning is complete, on withdrawal.
- Document all three segment scores plus the total in the endoscopy report, so the adequacy judgement can be checked rather than taken on trust.
- Where the preparation is inadequate, say so explicitly in the report and state a repeat interval — do not record standard surveillance.
- Repeat within one year after an inadequate preparation, and sooner where the prior probability of neoplasia is high.
- Review the regimen before the repeat: split-dose preparation, the interval between the last dose and the procedure, constipating medication, opioids, diabetes and previous inadequate preparations all change what to prescribe next time.
- Where the right colon specifically scored poorly, weigh that more heavily than the total when setting the repeat interval, regardless of what the arithmetic says.
- Audit the proportion of adequate preparations at unit level — it is a recognised quality indicator and an individual endoscopist cannot see their own rate without it.
Why this score exists
The authors' complaint about existing scales was specific: they had been designed to compare purgatives in drug trials, which meant they were scored before the endoscopist cleaned anything, and the endoscopist's washing and suctioning was therefore treated as noise. For a trial of two laxatives that is defensible. For a study asking whether preparation quality affects polyp detection it is exactly backwards, because the thing that determines detection is the view the endoscopist ends up with, not the view they started with. Two design choices follow directly: score on withdrawal after all cleansing, and score by segment rather than globally. Both were made to serve outcomes research, and the scale's adoption as a clinical quality metric came afterwards — which is worth knowing, because the segment-level adequacy rule that clinicians now rely on was not in the original paper at all. It was added five years later by the same group, once it became clear the scale needed an interpretable threshold and not just a number.
About the creator
First author, BBPS derivation
First author of the 2009 paper that developed and validated the scale.
Senior author, BBPS derivation and subsequent validation
Senior author of the derivation study and of the later work establishing the adequacy threshold.
Co-author; led the validation and adequacy-definition studies
Led the 2010 comprehensive validation and the 2014 study that defined a total of 6 or more with all segments at 2 or more as an adequate preparation.
Limitations
- Derived at a single academic centre, which the authors identified as the study's principal limitation.
- Inter-observer reliability of 0.74 is good but not excellent, so the same procedure scored by two endoscopists can land either side of the adequacy threshold.
- Segments are unweighted despite unequal clinical consequence — an unseen right colon and an unseen rectum cost the same three points.
- Requires a complete colonoscopy to caecal intubation; it has no way to express that a segment was not reached rather than not clean.
- Scoring depends on the endoscopist's own assessment of their own examination, which is a structural conflict when adequacy determines whether a repeat is needed.
- Does not record fluid volume separately, unlike the Ottawa scale, though pooled fluid obscures mucosa in a different way from adherent stool.
- The adequacy threshold was defined for detecting neoplasia in screening and surveillance; it is not specifically validated for other indications such as assessing inflammatory bowel disease extent.
- Says nothing about why the preparation failed, which is what determines the fix — regimen, timing, adherence or motility all produce the same low score.
If you are the patient
The Boston Bowel Preparation Scale is how your endoscopist records how clean your bowel was during a colonoscopy. The colon is divided into three parts, each given a mark out of 3, so the total is out of 9. The examination counts as good enough when the total is 6 or more and no single part scored below 2 — both matter, because if one section could not be seen properly it does not help that the others were spotless. The reason this is recorded is straightforward: polyps can only be removed if they can be seen, and a poorly cleaned bowel means small ones may have been missed. If the score shows the preparation was not good enough, you will usually be offered a repeat colonoscopy sooner — often within a year — rather than waiting the usual interval. That is not a criticism of you; preparation is affected by constipation, some medications, diabetes and simply how the timing of the doses worked out, and your team will usually adjust the plan for next time. The single most useful thing you can do is follow the timing instructions exactly, particularly taking the second dose on the morning of the procedure if you have been told to — the gap between the last dose and the test makes more difference than almost anything else.
Frequently asked questions
What is a good Boston Bowel Preparation Scale score?#
A total of 6 or more with every segment scoring at least 2 is the accepted definition of an adequate preparation. Totals of 7 to 9 with all segments at 2 or more represent good to excellent preparation. Mean BBPS in the derivation cohort of 633 screening colonoscopies was 6.0, so an adequate score sits close to average rather than being a high bar.
Is a BBPS of 6 always adequate?#
No — only if no segment scored below 2. A total of 6 made up of 3 + 3 + 0 is an inadequate preparation, because one segment was never visualised and a well-prepared segment cannot compensate for an unseen one. This conjunction is the most commonly misread part of the scale.
How is the BBPS scored?#
Each of three segments — right colon (caecum and ascending), transverse colon including both flexures, and left colon (descending, sigmoid and rectum) — is graded 0 to 3 and the scores are added, giving 0 to 9. Crucially, the scoring is done on withdrawal after all washing and suctioning is complete, not on the initial view.
What do the 0 to 3 segment scores mean?#
0 means the mucosa was not seen because of solid stool. 1 means part of the mucosa was seen but other areas were obscured. 2 means there was minor residual staining, small fragments or opaque fluid but the mucosa was seen well. 3 means the entire mucosa was seen well with no residual staining. Two is the minimum acceptable score for a segment.
When should a colonoscopy be repeated for poor bowel prep?#
When the preparation is inadequate — a total below 6, or any segment below 2 — the examination cannot be relied on to exclude significant pathology, and guidance is to repeat rather than apply standard surveillance intervals. Most guidelines advise repeating within one year, and sooner where the prior probability of neoplasia is high. A meta-analysis of adenoma miss rates by preparation quality supports early repeat rather than interval extension.
Why is BBPS scored after washing rather than before?#
Because what determines whether a lesion is found is the view the endoscopist actually had, not the state the patient arrived in. Earlier scales were designed to compare purgatives in drug trials, so they scored the initial view and treated endoscopist washing as a confounder. BBPS was built for outcomes research and deliberately scores after all cleansing manoeuvres.
Is the maximum BBPS score 9 or 10?#
The maximum total is 9 — three segments scored 0 to 3. The original paper describes it as a 10-point scale because there are ten possible totals, 0 through 9, which is a persistent source of confusion. If you see a score reported as x/10, the denominator is wrong.
How reliable is BBPS between different endoscopists?#
Good rather than perfect. The derivation study found an inter-observer intraclass correlation coefficient of 0.74 across 22 clinicians, and intra-observer weighted kappa of 0.77 (95% CI 0.66–0.87) when the same footage was rescored. That leaves enough variation for the same procedure to fall either side of the adequacy threshold depending on who scored it.
Does bowel preparation quality actually affect polyp detection?#
Yes. In the derivation cohort, scores of 5 or more were associated with a polyp detection rate of 40% compared with 24% below 5 (P < .02). Subsequent work has shown detection continues to differ across the range conventionally called adequate, so a total of 6 and a total of 9 are not equivalent examinations even though both pass the threshold.
References
Original / primary reference
Validation and evidence
- Calderwood AH, Jacobson BC. Comprehensive validation of the Boston Bowel Preparation Scale. Gastrointest Endosc. 2010;72(4):686-692.
- Calderwood AH, Schroy PC 3rd, Lieberman DA, Logan JR, Zurfluh M, Jacobson BC. Boston Bowel Preparation Scale scores provide a standardized definition of adequate for describing bowel cleanliness. Gastrointest Endosc. 2014;80(2):269-276.
- Clark BT, Rustagi T, Laine L. What level of bowel prep quality requires early repeat colonoscopy: systematic review and meta-analysis of the impact of preparation quality on adenoma detection rate. Am J Gastroenterol. 2014;109(11):1714-1723.
- Clark BT, Protiva P, Nagar A, Imaeda A, Ciarleglio MM, Deng Y, Laine L. Quantification of Adequate Bowel Preparation for Screening or Surveillance Colonoscopy in Men. Gastroenterology. 2016;150(2):396-405.