Dr K N Prasad Community Medicine Screening methods Dr K N Prasad Community Medicine

Diseases are having iceberg phenomenon Screening is the early detection of disease precursors to disease. Or susceptibility to diseases in individuals who do not show any signs of the disease Tests Questions Examinations Laboratory tests X rays

Definition: “The PRESUMPTIVE identification of UNRECOGNIZED disease or defect by the application of tests, exams or other procedures which can be applied RAPIDLY to sort out apparently well persons who PROBABLY have a disease from those who PROBABLY do not.” Screening refers to the application of a medical procedure or test to people who as yet have no symptoms of a particular disease, for the purpose of determining their likelihood of having the disease. The screening procedure itself does not diagnose the illness. Screening test will need further evaluation with subsequent diagnostic tests or procedures.

Differences Screening test Diagnostic test Done on apparently healthy Applied to groups Based on one or cut off criteria Less accurate Not a basis for treatment Initiative comes from the health agency Diagnostic test Done on those with sick or indications Applied to single patient Based on evaluation of number of symptoms, signs or lab tests More accurate Basis for treatment Initiative comes from patient with complaint

Lead time concept Time lag present between disease onset and usual time of diagnosis Final critical point Usual time of diagnosis Disease onset First possible detection outcome A Screening time B Lead time Lead time is the period between diagnosis by early detection and diagnosis by other means

Screening pathways Healthy Disease or precursor Detectable Symptoms develop Advance disease Death Screening possible Intervention to avert disease development or its consequences Life prolonged

Objective Examinations The goal of screening is to reduce morbidity or mortality from the disease by detecting diseases in their earliest stages, when treatment is usually more successful. Sort out the population who has risk from others Examinations Pap smear, Mammogram, Clinical breast exam, Blood pressure determination, Cholesterol level, Eye examination/vision test, and Urinalysis.

Uses of screening tests Cases detection (Prescriptive ) Screened primarily for their own benefit Ex. Neonatal, cancers Control of diseases (Prospective) Screened for benefit of others Ex. STD, TB Research purpose May aid in obtaining basic knowledge about natural history of disease Education opportunity To create public awareness and educating health professionals

Types of screening Mass screening High risk or selection screening Screening afford to all irrespective of the particular risk Ex. TB High risk or selection screening Applied to selective high risk group on the basis of epidemiological research Ex. Cervical Cancer, heart diseases Multi purpose screening Application of two or more tests in combination to a large number at one time Ex. Questionnaire, examination, laboratory tests etc.

Criteria for population based screening Knowledge of disease Condition must be an important problem Presence of recognisable latent or early symptomatic stage Natural history of the condition must be adequately understood Feasibility of screening procedures Suitable test or examination Acceptable to the population Should be a continuous process

Contd. Diagnosis and treatment Cost considerations acceptable treatment with recognisable disease Facilities for diagnosis & treatment should be available agreed upon policy to treat as patients Cost considerations adequate resources Expected benefit

Principles Condition should be an important public health problem There should be a recognizable early or latent stage There should be an accepted treatment for persons with condition The screening test is valid, reliable and acceptable yield The test should be acceptable to the population to be screened The cost of screening and case finding should be economically balanced in relation to medical care as a whole

Screening tests Acceptability : Repeatability Simple, minimum pain or discomfort, easy, safety, rapidity , acceptable procedure, etc. Repeatability Must give consistent result when repeated several times on the same subject or individual Observer variation Biological variation

Observer variation Intra observer or within observer variation Measurements should be same( subject or material) if recorded several times at that time or event Ex. Ht, wt, lab tests. etc.. Inter observer variation or between observer variation Differences in measurements on the same ( subject or material) by different investigators Ex. X ray, blood smears, organisms, etc..

Biological variation Variation in physiological variables. Ex. BP, Rates, etc. Changes in parameters observed Ex. MI, Cancers, etc Variations in their symptoms /signs Memory, pain, quality of care, etc. Regression to the mean Tendency of values merge at the mean. This is tested by repeated observation over time

Thought for the day Every job is a self portrait of the person who did it. Autograph your work with excellence.

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Difference Screening test is intended for initial examination. Diagnosis involves confirmation of presence or absence of disease in someone suspected or at risk for having a disease. Case finding measures