Diagnostics 1&3 Flashcards
Definition of a diagnostic
A characteristic of an illness or phenomenon (e.g symptoms, signs and biomarkers)
Why do we do tests?
To include or exclude disease, support management, prognosis, monitoring or measure of general health
5 approaches to defining normality
Statistical/Gaussian normality, percentile, risk factor, diagnostic, therapeutic
What is Gaussian distribution?
Normal distribution - defining normality by proximity to the mean in the population (bell curve)
Percentiles
Defining normality by proximity to the median - useful if mean is effected by data skew
Defining normal by diagnosis
Comparing values found in healthy to those found in disease -often overlap though and often levels often raised in sick people without the disease
100% sensitivity cut off
Positive result in all cases of disease (can get false positives)
100% specificity cut off
Negative in all those without disease (can get false negatives)
Compromise cut off
Minimising false positives and negatives
Defining normal by therapeutic benefit
Normal if no benefit from treatment - must also consider harm of treatment so look at net benefit - useful if immediate treatment not necessary
What is D-Dimer?
Small protein fragment found i blood after a clot. Degradation product of fibrin not found in normal blood
Examples of gold standard tests
Histology, imaging and genetics
Problems with histology
Interpretation and observer bias
Problems with imaging
Interpretation, observer bias and incidental findings
Problems with genetic tests
Normal variation, variable penetration and phenocopy (Other genes can cause same phenotype)
