Lili Yuxi Ren. Reference Librarian, The Hospital for Sick
Children, Toronto ON. Email: firstname.lastname@example.org
This article is distributed under a Creative Commons Attribution License.
Product: Isabel Pro – the DDX Generator
Cost: Free 30-day trial,
Standard individual subscription USD $149/yr Premium individual subscription USD $219.99/yr Institutional subscription also available
Isabel Healthcare began in 1999 as a non-profit organization
after its founder Dr. Mark Graber’s daughter suffered a near fatal
misdiagnosis. In 2004, the organization converted to a for-profit
business to support individual healthcare providers, and
institutions including hospitals and medical schools. Isabel Pro
or differential diagnosis (DDX) generator (henceforth, Isabel Pro)
is a web-based diagnosis decision-making tool as part of the
Isabel product suite of diagnosis decision support systems.
Instead of rules-based algorithms, Isabel Pro uses statistical
natural language processing (SNLP) to provide diagnosis retrieval
for physicians and healthcare providers to avoid “System 1
diagnosis errors” in clinical settings. Sample cases can also be
built to support the teaching of medical students and residents.
Patients can use the free Isabel Symptom Checker to make sense of
and research their symptoms. It allows patients to describe their
symptoms in plain language and helps patients figure out their
next steps (e.g. visit a clinic, visit the emergency, etc.). This
product review is intended for the former product, Isabel Pro.
Isabel Pro is a software tool that uses SNLP engine to search in
a database of disease presentations or illness scripts for
physicians. Isabel Pro determines likely diagnosis based on the
patient’s demographics and clinical features, including
time-sensitive “Don’t Miss Diagnoses.”
Symptoms can be searched using natural language in a database of over 10 000 diagnoses of which 6 000 are diseases and 4 000 are drugs. The database is manually built and populated with knowledge about each disease from different sources. It does not give a sufficient precision but, instead, presents different potential diagnoses and match rates.
The interface is intuitive to use. It takes information entered
and matches it across electronic sources to create a checklist of
potential diagnoses. For teaching purposes, cases can also be
generated and uploaded to Isabel Pro to support students in the
diagnosis decision-making process. Additional training and support
are also available from Isabel representatives.
The search feature has the ability to retrieve results using
natural language. Physicians can begin the differential diagnosis
process by entering patient data (e.g. age, gender, pregnancy
status, travel history) into the “Clinical Features” box. Next,
physicians can enter “Abnormal Clinical Features” including chief
complaints, common medical abbreviations such as SOB (i.e.
shortness of breath), labs, vitals, and comorbidities extracted
from the patient’s medical record. The search box can also
directly link to a library’s subscription of evidence-based
By clicking on the “Get Checklist” button, the system generates a
ranked list of diagnoses arranged by a color bar of “Likelihood
Indicator.” Outputs are filtered for the relevant age, gender, and
region of the patient. The list can also be sorted by specialty or
red flags (i.e. conditions requiring immediate attention). In a
separate tab, drug side effects that may have caused the symptoms
are also listed.
Fig.1. Isabel Pro user interface
In the options listed on the right of the ranked diagnoses, every
generated differential diagnosis can be emailed, printed, saved,
or copied. The interface also allows users to provide direct
feedback to Isabel representatives through a “feedback” icon on
Medical publishers have also partnered with Isabel Healthcare to
provide links to resources a library may have, including Minute
Consult from Wolters Kluwer, DynaMed Plus from EBSCO, and Best
Practice from the British Medical Journal (BMJ).
A 34-year-old woman who was 14 weeks pregnant presented to the
emergency department with 5 days of nonspecific abdominal pain,
nausea, vomiting. On examination, she appeared well with normal
vital signs and had some mild diffused abdominal tenderness.
As test results are added, Isabel Pro produces a modified ranked
list of diagnoses. Acute appendicitis and peritonitis move up on
the ranked listed and highlighted in dark orange as “most likely”
Users can click on each diagnosis to access knowledge resources
integrated into Isabel Pro.
Fig.2. Isabel Pro results based on initial clinical features
Fig.3 Isabel Pro results after lab test results added
Fig.4 Pop-up window of knowledge resources for a selected diagnosis
The tool has the capability to integrate with many popular
databases, clinical tools, and library resources such as PubMed,
Embase, MEDLINE, UpToDate, DynaMed, Lexicomp, Micromedex, CDC, and
TRIP. When integrated with DynaMed or UpToDate, results will link
directly to relevant DynaMed or UpToDate topics. If neither is
available, the links will resort to PubMed.
Isabel Pro can be integrated in an electronic medical records
(EMR) system. Data from pre-assigned EMR fields can be submitted
to Isabel Pro using the Isabel User Interface. Current EMR vendors
that offer an Isabel interface are Epic, Cerner, NextGen,
Allscripts, SystmOne, T-Systems, Better Day, and VersaSuite.
Isabel Pro is selected by the American Medical Association
(AMA) as the diagnosis tool for its portal and endorsed by the
British Medical Journal (BMJ). The tool undergoes continuous
validation processes, including controlled trials and
peer-reviewed studies, covering various aspects of the system. For
users, the Isabel Healthcare support team provides on demand
support, customizable interfaces using the Isabel API, and
seamless integration with a library’s databases, clinical tools
and resources, or EMR system. Users can also capture and print
what they learned in Isabel Pro for a credit to be issued towards
their continuing medical education (CME).
While Isabel Pro is intuitive and user-friendly, knowledge of medical terms may be a drawback for some users. It can also be costly for individuals and institutions on top of their existing subscriptions. For the full potential use of the tool, it is best integrated with other resources, most of which require a library subscription.
A number of Isabel Healthcare and independent studies have
studied the usefulness of Isabel Pro for attending physicians,
residents, nurses, and medical students in the diagnosis
decision-making process. A summary of findings is listed below.
The literature on DDX generators is complex, with a variety of
study designs. The lack of standardized appraisal and criteria for
DDX generators often result in poor quality and insufficient
evidence from the existing literature to recommend the routine use
by physicians. DDX generators are not intended to replace
physicians but rather augment the diagnosis decision-making
process. Further studies that examine the efficacy, ranking of
diagnoses, cost-effectiveness, and time should be addressed before
further recommendations can be made.
DDX generators have moved away from rules-based systems that were
developed in the 1970s and 1980s. Tools, such as DxPlain, QMR,
Meditel, and Diagnosis Pro, tend to associate each symptom with a
particular disease and assigned probability. On the other hand,
Isabel Pro is part of a new generation of tools that uses natural
language pattern recognition through a database of diagnosis
presentations to provide a list of ranked diagnoses. A competing
tool similar to Isabel Pro is VisualDx, which is a system
primarily based on digital images and allows physicians and
clinicians to build visual differential diagnosis based on the
patient’s test findings.
Isabel Pro is web-based and compatible with all browsers and
mobile platforms. While no mobile app is available, users can save
a shortcut of a web link to their device’s home screen for easy
Database contains 10 000 diagnoses including 6 000 diseases and 4
000 drugs. Records are updated on a weekly and monthly basis with
submissions from 30 different sources, including Isabel
Healthcare, users, and physicians.
Isabel Pro is a subscription-based product. Annual individual
subscriptions are available for two versions: standard USD $149/yr
and premium USD $219.99/yr. The premium package includes access to
5 Minute Consult. Institution subscriptions are negotiated for
each institution. Discounts are also available for students.
To discuss your library’s needs, please contact an Isabel
Healthcare representative for an inquiry or visit
Thanks to Patrick Garrett, Isabel Sales Associate, for providing
a product demo and addressing follow-up questions.
No competing interests declared.
1. Amy, L. R., Borowitz, S. M., Brown, P. A.,
Mendelsohn, M. J., & Lyman, J. A. (2006). Impact of a
Web-based diagnosis reminder system on errors of diagnosis. AMIA
... Annual Symposium proceedings. AMIA Symposium, 2006, 843.
2. Bond, W. F., Schwartz, L. M., Weaver, K. R., Levick, D., Giuliano, M., & Graber, M. L. (2012). Differential diagnosis generators: an evaluation of currently available computer programs. Journal of General Internal Medicine, 27(2), 213-219.
3. El-Kareh, R., Hasan, O., & Schiff, G. D. (2013). Use of health information technology to reduce diagnostic errors. BMJ Quality & Safety, 22(Suppl 2), ii40-ii51.
4. Henderson, E. J., & Rubin, G. P. (2013). The utility of an online diagnostic decision support system (Isabel) in general practice: a process evaluation. JRSM Short Reports, 4(5), 1–11.
5. Ramnarayan, P., Cronje, N., Brown, R., Negus, R., Coode, B., Moss, P. Britto, J. (2007). Validation of a diagnostic reminder system in emergency medicine: a multi-centre study. Emergency Medicine Journal: EMJ, 24(9), 619–624.
6. Riches, N., Panagioti, M., Alam, R., Cheraghi-Sohi, S., Campbell, S., Esmail, A., & Bower, P. (2016). The effectiveness of electronic differential diagnoses (DDX) generators: a systematic review and meta-analysis. PloS one, 11(3), e0148991.
7. Semigran, H. L., Linder, J. A., Gidengil, C., & Mehrotra, A. (2015). Evaluation of symptom checkers for self diagnosis and triage: audit study. British Medical Journal, 351, h3480.