Clinical utility Flashcards
Why are people tested for a disease? (4)
Screening
Diagnosis
Monitoring
Prognosis
Factors that impact the correct result of a test:
Pre-analytical- technical and/or biological
Analytical factors- accuracy + precision
Post-analytical factors- reporting
4 technical pre-analytical factors:
correct identification of patient
correct collection of specimen
Accurate labelling
Rapid + secure transport
Pre-analytical biological factors:
Endogenous (4) + Exogenous (5)
Endogenous: Age Gender Body Mass Ethnic origin
Exogenous: Time-dependent changes Stress Posture food intake drugs
Post analytical errors: (4)
Transmission of report
Transcription of report (over phone)
Interpretation of data
clinical decision
The usefulness of a biochemical test is evaluated by 2 measures:
Clinical sensitivity: DEFINITION
Clinical specificity: DEFINITION
What do these two things describe? SHORT ANSWER
Clinical sensitivity: The proportion of positive test results in the diseased group expressed as a %.
Clinical specificity: The proportion of negative test results in the healthy group expressed as a %.
These describe how well the test discriminates patients with and without a disease
True positives (TP) are... True negative (TN) are... False positives (FP) are... False Negatives (FN) are... Number of people with the disease = ? Number of people without the disease = ? Number of positive tests = ? Number of negative tests = ?
Individuals with the disease Individuals without the disease Healthy individuals who test +ve for the disease Diseased individuals who test -ve for the disease TP + FN TN + FP TP + FP TN + FN
Sensitivity: EQUATION + MEANING
(TP/(TP+FN)) x 100
Proportion of positive results in diseased population.
What is the clinical cut-off/decision threshold?
What are the consequences if it is higher?
What are the consequences if it is lower?
The concentration of a specified bio-marker that determines whether a patient is recorded in the healthy population or the diseased population.
Fewer FPs increase specificity, but greater number of FNs decrease sensitivity.
Fewer FNs increase sensitivity, but greater number of FPs decrease specificity.
Specificity: EQUATION + MEANING:
(TN/(TN + FP)) x 100
Proportion of negative results in disease free population.
The efficiency of a test is…
EQUATION =
This basically means…
The fraction of of individuals correctly assigned as either having, or being free from a disease.
(TP + TN)/(TP + FP + TN + FN).
Proportion of total correct results.
When should the test with the greatest efficiency be used?
When sensitivity + specificity are equally as important
False positive rate: DEFINITION
False negative rate: DEFINITION
The proportion of people, among those who are responding positive to a test who are actually free of the disease.
The proportion of people, among those who are responding negatively to a test who nevertheless have the disease.
False positive rate: EQUATION
FP/(FP + TN)
False negative rate: EQUATION
FN/(TP + FN)
