IBD Resources Hub
Menu

Find organisations and helplines in your country:

CDAI Calculator

The score many gastroenterologists use for Crohn’s disease in adults, worked out from a week of symptoms, one blood test and your weight.

The Crohn’s Disease Activity Index (CDAI) is a score from 0 to about 600 that describes how active Crohn’s disease has been over the last 7 days. It was developed in the 1970s for research, and it is still used by gastroenterologists and, in Australia, New Zealand and the UK, in the rules for some funded Crohn’s medicines.

Most of it comes from things only you know: how many liquid or very soft stools you had, how much pain, and how you felt, each day for a week. Keeping a daily note for the 7 days before an appointment makes these items much easier to fill in. The rest comes from a recent blood test (haematocrit), your weight, and an examination by your doctor.

Work out your CDAI score

The score’s blood test items use different normal ranges for males and females.

Australia’s PBS form expects all 7 days, so leave this off if the score is for a PBS application.

Liquid or very soft stools (poos)

The number each day, for the last 7 days.

Points: the 7-day total × 2.

Abdominal (tummy) pain

How bad it was each day, for the last 7 days.

  • 0 None
  • 1 Mild
  • 2 Moderate
  • 3 Severe

Points: the 7-day total × 5.

General wellbeing

How you felt overall each day, for the last 7 days.

  • 0 Generally well
  • 1 Slightly below par
  • 2 Poor
  • 3 Very poor
  • 4 Terrible

Points: the 7-day total × 7.

Joint pain or swelling (arthritis or arthralgia)
Eye inflammation (iritis or uveitis)
Skin or mouth problems linked to Crohn’s (such as erythema nodosum, pyoderma gangrenosum or mouth ulcers)
Problems around the anus (a fissure, fistula or abscess)
Any other fistula
A temperature over 37.8 °C (100.0 °F) in the last week
Taking medicine to slow diarrhoea (such as loperamide, diphenoxylate or codeine)
Lump (mass) in the abdomen, found when your doctor examines you From your IBD team: leave it blank if you don’t know
Haematocrit, from your most recent blood test

It may be printed as Hct, HCT or PCV (packed cell volume). Type it as it’s printed on your report: 0.42 (L/L) and 42 (%) both work.

Points: (47 − haematocrit in %) × 6 for males, (42 − haematocrit in %) × 6 for females. A result in L/L counts as a percentage (0.42 L/L is 42%).

Body weight compared with your standard weight

In the original study, standard weight was your weight before Crohn’s disease started or, if that isn’t known, an average weight for your sex, age and height. Your IBD team may use a different figure, and theirs is the one that counts. Without a standard weight, this item can’t be scored.

Don’t know your weight before Crohn’s? Some teams use a healthy weight for your height instead, which an official calculator shows. That isn’t the original study’s method, so check the figure with your IBD team.

Points: 100 × (1 − current ÷ standard); with the limit ticked, never below −10 (a cap that Australia’s PBS form and most later trials add; the original study has none).

How the CDAI score is used where you live

Australia

In Australia, many medicines are subsidised through the Pharmaceutical Benefits Scheme (PBS). The PBS asks for a CDAI score when a specialist applies for some subsidised Crohn’s medicines, through the PBS’s online system or by phone. For some of them, the PBS rules use a score of 300 or more (220 or more with extensive small-bowel disease). Source: PBS: Crohn disease (item 12345R).

Canada

In Canada, provincial drug plans and private insurers set their own rules for some Crohn’s medicines, and some of them ask your specialist for a disease activity score.

New Zealand

In New Zealand, Pharmac, the government agency that decides which medicines are funded, asks for a Special Authority form for some of them. One of Pharmac’s Special Authority forms, for example, uses a CDAI of 300 or more (or a Harvey-Bradshaw Index of 10 or more) to start treatment, and a fall of 100 points or a CDAI of 150 or less to continue it. Source: Pharmac: Special Authority form SA2183.

United Kingdom

In the UK, the National Institute for Health and Care Excellence (NICE) advises the NHS in England and Wales on which medicines to use; Northern Ireland reviews its advice, and Scotland has its own body, the Scottish Medicines Consortium (SMC). NICE guidance on some Crohn’s medicines says severe active Crohn’s disease normally, but not always, matches a CDAI of 300 or more. Source: NICE technology appraisal TA187.

United States

In the US, health insurers set their own rules for approving some Crohn’s medicines, and some ask your doctor for a disease activity score.

Somewhere else

Where you live, your IBD team may use this score, or a similar one, to track how active Crohn’s disease is and when planning treatment.

What the total means

The CDAI score describes how active Crohn’s disease looks from the answers given. It doesn’t diagnose anything, and your IBD team reads it alongside everything else they know about you.

  • 150 or under: the range the original study linked with quiescent (inactive) disease
  • Over 150 and under 220: the range later studies call mild
  • 220 to 450: the range later studies call moderate
  • Over 450: the range the original study linked with extremely severe disease

Sources