SCREE

NIN

G

the presumptive identification of unrecognized disease or defect by the application of tests, examinations or other procedures which can be applied rapidly to sort out those who probably have the disease from those who probably do not

Definition

Criteria for screening Test has high sensitivity and specificity Test meets acceptable standards of

simplicity, cost, safety and patient acceptability

Disease that is focus of screening should be sufficiently serious in terms of incidence, mortality, disability, discomfort, and financial cost

Evidence suggests that the test procedure detects the disease at a significantly earlier stage in its naturally history than it would present with symptoms

A generally accepted treatment that is easier or more effective than treatment administered at the usual time of symptom presentation must be available

The available treatment is acceptable to patients as established by studies by studies on compliance with treatment

Prevalence of the target disease should be high in the population to be screened

Follow up diagnostic and treatment service must be available and accompanied by an adequate notification and referral service for those positive on screening

Characteristics of a diagnostic test

AccuracySimplicityCostSafetyAcceptability

Accuracy of a screening

The test should give a true measurement of the attribute under investigation and provide consistent results in repeated trials more over it should have high sensitivity and specificity for the disease in question

Specificity—The ability of a test to give a positive finding when the person is tested truly has the disease under study

Sensitivity—the ability of a test to give a negative finding when the person tested is free from the disease under study

sensitivity and specificity both expressed in %

CALCULATING SPECIFICITY AND SENSITIVITY

The fourfold contingency table is used

SPECIFICITY

SENSITIVITY

PREDICTIVE VALUES

Positive Predictive Value is the probability that patients with a positive screening test truly have the disease

Negative Predictive Value is the probability that patients with a negative screening test truly do not have the disease

REFERENCES

http://gim.unmc.edu/dxtests/howto.htm

http://www.fpnotebook.com/Prevent/Epi/TstSnstvty.htm

http://sphweb.bumc.bu.edu/otlt/MPH-Modules/EP/EP713_Screening/EP713_Screening5.html#positiveandnegativepredictivevalue 

Thorner and Remein. Principlesand Procedures in the Evaluation of Screening for Disease, US Department HEW, Public Health Monograph No. 67, 1961

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