Sensititvity and Specificity

Analytical sensitivity

The smallest amount of a substance in a sample that an assay can accurately measure

Analytical specificity

Ability of an assay to determine specifically the concentration or detection of the together analyze in the presence of interfering substance

Cross reactivity

When primers designed to amplify one specific target are successful in amplifying another, different target

Interference

When a sample contains endogenous substances that can inhibit the assays’ ability to perform correctly (may lead to false negatives)

Clinical sensitivity

Fraction of patients with a disease that the assay correctly indentifies

Clinical specificity

Fraction of patients whiteout a disease that the assay correctly indentifies

%sensitivity

Proportion of positive tests among patients that have the disease

%sensitivity equation

True pos/ (truepos + false neg) x 100%

%specificity

Proportion of negative tests among patients that are healthy

%specificity equation

Trueneg/ (Falsepos + trueneg) x100%

What does the positive predictive value do

Tells us if a lab test can correctly predict a disease

Equation for PPV

Truepos / (TruePos + FalsePos) x 100%

Disease prevalence equation

TP + FN / TP+FN+FP+TN