Rational of clinical examination

1. RATIONAL OF CLINICAL
EXAMINATION
A Primer on the Precision and Accuracy of the Clinical
Examination
Sujan Kafle
MDGP resident
1st year

2. • A patient is scheduled for orthopaedic surgery in 30 minutes ,
you stop by to see him. He is alert and hemodynamically
stable but you noticed that he smells of alcohol and he has
three spider nevi on his upper chest.
• DOES HE HAVE ASCITIES?
• IS THIS MAN AN ALCOHOLIC?
• ARE THESE QUESTIONS IMPORTANT?

3. Investigations
Alcohol dependence Ascities
• Complete history taking
• Liver function test
• Platelete enzyme activity
• CAGE question
• Abdominal examination
• Abdominal ultrasonography
• History of ankle swelling
WHICH ONE DO WE CHOOSE????

4. Tools
• Sensitivity
• Specificity
• Positive predictive value
• Negative predictive value
• Likelihood ratio

6. Sensitivity
It is a useful measure of how well a diagnostic test (whether a
symptom, sign, or laboratory test) detects a target disorder
when it is present.
The closer the sensitivity to 100%, the more “sensitive” the
clinical or laboratory finding.
a/(a+c)

7. Specificity
It is a useful measure of how often a symptom, sign, or other
diagnostic test is absent when the target disorder is not present.
The closer the specificity to 100%, the more “specific” the
clinical or laboratory finding.
• d/(b+d)

8. Pretest probability
• Estimate of patients having the disease before conducting the
test.
• (a+c)/(a+b+c+d)

9. Positive predictive value
• The ratio of patients truly diagnosed as positive to all those
who had positive test results
• Post test probability of having the target disorder.
• a/(a+b)

10. Negative predictive value
• The ratio of patients truly have negative test to all those who
had negative test results
• Post test probability of not having the target disorder
• d/(c+d)

11. Calculate sensitivity, specificity, positive and negative
predictive value from the following?
Disease
present
Disease absent
Test positive 900 100 1000
Test negative 100 900 1000
1000 1000 2000

13. Presence of ascities on abdominal ultrasonography
History
Of
Ankle
swelling
Present Absent
Yes 14 16 30
No 1 32 33
15 48 63

14. • Sensitivity 93%
• Specificity 67%
• Pretest probability 24%
• Positive predictive value 47%
• Negative predictive value 97%

15. Likelihood ratio:
• Expression of sensitivity and specificity that can be used to
estimate the odds that a condition is present or not

16. Advantages
1 Generates the post test odds for the disorder from the pretest
odds
• Pretest odd= (probability of having the target
disorder)/(probability of not having the target disorder)
• Pretest odds * likelihood ratio= posttest odds
• Post test probability= (post test odds)/(post test odds +1)
• CAN BE EASILY CALCULATED BY NOMOGRAM!!!

18. positive negative Likelihood ratio
a x (a/Tpositive)/(x/Tnegative)
b y (b/Tpositive)/(y/Tnegative)
c z (c/Tpositive)/(z/Tnegative)
Tpositive Tnegative

20. ALCOHOLABUSE OR DEPENDENCY
Answer to
the
CAGE
Questions
Yes No
3 or 4 60 1 61
2,1 or none 57 400 457
117 401 518

21. ALCOHOL ABUSE OR DEPENDENCY
Answer
to the
CAGE
Question
s
Yes No
3 or 4 60 1 61
2,1 or
none
57 400 457
117 401 518

22. • Sensitivity 51%
• Specificity 99.8%
• Pretest probability 23%
• Positive predictive value 98%
• Negative predictive value 88%

23. • Positive likelihood ratio 51
• Negative likelihood ratio 0.49

24. THANK YOU