School for Primary Care ResearchIncreasing the evidence base for primary
care practice
Carl Heneghan
Diagnostic Reasoning forEvidence-Based Practice.
Background
The strategies clinicians use to arrive at a diagnosis makes only asmall contribution to current research and the medical curricula.
Debate still exists about our understanding of the complex strategiesused in diagnostic reasoning.
Determining diagnostic strategies is particularly pertinent wherepatients present with an array of conditions and possible diagnoses.
Our aim was to set out - for a forthcoming series of diagnosticarticles - the strategies and methods that are employed in routineclinical consultations.
What we did
1st phase: focus group of GPs and researchers in primary care toidentify several strategies - based on consensus opinion and thepublished literature - used in diagnosis.
Strategies mapped in a consecutive series of 100 patients by 1 GP(CH).
2nd phase: From phase 1 a model incorporating 3 stages used indiagnosis formulated.
Six GPs recorded data using a revised data collection sheets for 50clinical consultations.
Final focus session using a consensus development approach.
Spot diagnosis Self-label Presentingcomplaint
Pattern0%
10
%2
0%
30
%4
0%
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%6
0%
70
%8
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90
%1
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%
Figure 2: initiation of the diagnosis
% strategy used by GPS and overall mean
Diagnostic stages & Strategies
Self-labelling
Tonsillitis – had it before
I have a chest infectiondoctor
Groin strain
I have asthma
I have a uti – just like lasttime
Spot diagnosis Self-label Presentingcomplaint
Pattern0%
10
%2
0%
30
%4
0%
50
%6
0%
70
%8
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90
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Figure 2: initiation of the diagnosis
% strategy used by GPS and overall mean
Diagnostic stages & Strategies
Prediction rules: which ones do you use in
practice?
Would be useful to have them all in easily accessibleformat.
I find the pictures very helpful, they help me rememberwhere to look for tenderness.
If you have a prediction rule, the way you take the historychanges... you go for the 3-4 things.
I would like to use them as guidelines for teachingstudents.
Clinical prediction guides project
Balla J, Glasziou P, Heneghan C.
Pattern recognition fit
49 yr old with severe flare up of Ulcerative colitis
Intravenous hydrocortisone, aminosalicylates, and ciclosporintreatment was started, and after seven days oral prednisolone
was introduced.
Is the use of a specific but probably imperfectsymptom, sign or diagnostic test to rule in or out adiagnosis.
Used in less than 10% of cases. Onepossible reason for this is that a certainamount of informal probabilisticreasoning was not recognized during theclinical consultation
(informal refers to reasoning not based on numerical understanding, but relieson decision making based on qualitative information, e.g. the disease is more orless likely).
Probabilistic reasoning:
Murtagh’s Stepwiserefinement
Probability Pattern CP rule0%
10
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0%
30
%4
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%6
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Figure 3: Refinement of the diagnosis
%strategyusedbyGPSandoverallmean
Refinement strategies
% strategy used by GPs (mean)
Spot diagnosis Self-label Presentingcomplaint
Pattern0%
10
%2
0%
30
%4
0%
50
%6
0%
70
%8
0%
90
%1
00
%
Figure 2: initiation of the diagnosis
% strategy used by GPS and overall mean
Diagnostic stages & Strategies
Strategies employed at the final diagnostic stage,
known diagnosis
ordering of further tests
test of treatment
test of time
In some cases the final
diagnosis cannot be
given a label
Known
Diagnosis
Furthertestsordered
Test oftreatment
Test oftime
No Label
10
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90
%1
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%
Figure 4: Defining the final diagnoses
The subsequent evolution of clinical features overtime is reviewed to see if the clinical features resolveor a particular diagnosis later becomes more obvious.
Thompson et al. Clinical recognition of meningococcal disease in children andadolescents. Lancet. 2006 Feb 4;367(9508):397-403
Test ofTime
TimeZero
VagueSigns
present
VagueSymptoms
present
IndeterminateInvestigations
Classical symptomsand signs present
Investigationspositive
BMJ diagnostic reasoning series
Diagnostic Reasoning|: Heneghan C, Glasziou P, Thompson M, Balla J,Rose P, Scott C, Lasserson D, Perera R.
Restricted Rule Out: Thompson M, Harnden A and Del Mar C Test of Treatment: Glasziou P, Rose P, Heneghan C, Balla J. Clinical Prediction Rules Fahey T Dan Mayer D Test of Time: Nick Summerton. Probabilistic Reasoning: Doust J. Self diagnosis: Spot” Diagnosis: a rapid but unreliable process: Glasziou P,
Heneghan C, Del Mar CB.