You see a 29 year old woman in an outpatient clinical 3 months after she has been diagnosed as having Crohn’s disease. She is married with two young children. Having adjusted to the initial shock of learning about her diagnosis and recovering from a bout of ilieitis she has read about all the potential complications of Crohn’s disease and is very concerned that her life expectancy will be greatly reduced. She says “I’ve read about all these bad problems, what are the chances of me dying young?”
You formulate the question, in a woman with Crohn’s disease, what is the risk of death? You search MEDLINE using the terms “Crohn’s Disease” and “survival” and find an article which appears to address her questions.
Searching Best Evidence on Disk with the single word “ferritin” yielded a very encouraging meta-analysis of 55 studies and a nice individual study, but your library didn’t carry either journal. You perform a MEDLINE search using the MeSH terms “ferritin” and “sensitivity and specificity” and find an article on diagnosing iron deficiency anaemia in the elderly published in a journal that your library does take
Gastroenterology 1998;114:1161-1168.
Read the article and decide:
- Is this evidence about prognosis valid?
- Is this valid evidence about prognosis important?
- Can you apply this valid and important evidence about prognosis in caring for your patient?
Completed Prognosis Worksheet for Evidence-Based Gastroenterology and Hepatology
Citation
Loftus EV, Silverstein MD, Sandborn WJ, et al. Crohn’s Disease in Olmstead County Minnesota, 1940-1993: Incidence, Prevalence, and Survival.
Gastroenterology 1998;114:1161-1168.
Are the results of this prognosis study valid?
- Was a defined, representative sample of patients assembled at a common (usually early) point in the course of their disease?
- Yes – 90% of the population are seen at the Mayo clinic in any 3 year period and record linkage ensures good coverage. Date of onset of symptoms was identified.
- Was patient follow-up sufficiently long and complete?
- Yes-minimum of 1 year but records from 1940 onwards were reviewed. Median follow-up=13.3 years (0.1-51.3).
- Were objective outcome criteria applied in a “blind” fashion?
- Death certificates were obtained for all patients who died. Causes of death were recorded (table3).
- If subgroups with different prognoses are identified, was there adjustment for important prognostic factors?
- No. No difference in survival was observed according to year of diagnosis or sex.
- Was there validation in an independent group (“test-set”) of patients?
- No
Are the valid results of this prognosis study important?
- How likely are the outcomes over time?
- 43 patients died (19%). Survival was slightly less than expected:
20 year survival 73%; expected 86%
30 year survival 73%; expected 74%
Only survival for patients diagnosed between 1963 and 1974 was less than expected. - How precise are the prognostic estimates?
- Not stated.
If you want to calculate a Confidence Interval around the measure of Prognosis
| Clinical Measure | Standard Error (SE) | Typical calculation of CI |
|---|---|---|
|
Proportion (as in the rate of some prognostic event, etc.) where:
The number of patients = n the proportion of these patients who experience the event = p |
$$ sqrt{frac{ptimes(1-p)}{n}}$$ text{where $p$ is proportion and $n$ is number of patients} |
$$text{If $p$ = 43/226 = 0.19( or 19%) and $n$=226}$$ $$mathit{SE}= sqrt{frac{0.19times(1-0.19)}{226}}$$ $$= 0.026 (or 2.6%)$$ $$text{95% $CI$ is 19% $pm$ 1.96 $times$ 2.6% or 13.9% to 24.1%}$$ |
Can you apply this valid, important evidence about prognosis in caring for your patient?
- Were the study patients similar to your own?
- Yes
- Will this evidence make a clinically important impact on your conclusions about what to offer or tell your patient?
- Yes
Additional Notes
–
Crohn’s Disease – Overall survival may be reduced
Clinical Bottom Line
Overall survival for Crohn’s disease patients is 92% of that expected but only for patients diagnosed before 1974.
Citation
Loftus EV, Silverstein MD, Sandborn WJ, et al. Crohn’s Disease in Olmstead County Minnesota, 1940-1993: Incidence, Prevalence, and Survival.
Gastroenterology 1998;114:1161-1168.
Clinical Question
In a patient with newly diagnosed Crohn’s disease what are the chances of dying prematurely?
Search Terms
“crohn’s disease” and “survival” in Medline
The Study
- 226 pts registered in a community-based Crohn’s registry and followed prospectively for median of 13.4 years (range, 0.3-51.3) after diagnosis.
- The Outcome: death
- Well-defined sample at uniform (early) stage of illness? yes;
- Follow-up long enough? yes;
- Follow-up complete? reasonably (20% drop out);
- Blind and objective outcome criteria? yes;
- Adjustment for other prognostic factors? no;
- Validation in an independent “test-set” of patients? no
The Evidence
| Prognostic Factor | Outcome | Time | Measure | Confidence Interval |
|---|---|---|---|---|
| Crohn’s disease | Death | 13.4 years | 19% | 13.9% to 24.1% |
Comments
- Decreased survival only applies to patients diagnosed before 1974
- 90% of Olmstead population included
- Rely on diagnosis of Crohn’s
- 20% lost in follow-up
- US study ? applicable worldwide?
- Small numbers in more recent decennial cohorts
