2* HIV testing – voluntary Mandatory testing – counterproductive Informed consent prior to testing is essential to deal with issues like-ConfidentialityDiscriminationVictimizationPsychological harm* HIV testing – voluntaryMandatory testing – counterproductive
5PPTCT Pregnant HIV infected women can- make informed decisions about dealing with pregnancyreceive appropriate and timely interventions to decrease MTCTensure safe deliverysecure early access to HIV care and treatmenteducated in prevention of HIV transmissionreceive follow-up health care for self and childPregnant HIV non infected women can be educated and counselled to remain uninfected
7Tests for detecting HIV INFECTION Detection of specific antibodiesscreening tests: 100% sensitivesupplemental/ confirmatory tests-sens. > 99.8%spec. > 98.5%Detection of specific antigens
8Accuracy with which a test can confirm the presence of an infection. SELECTION OF TESTS : BASED ON SENSITIVITY ,SPECIFICITY,EFFICIENCY,PPV & NPVSensitivity –Accuracy with which a test can confirm the presence of an infection.Test with high sensitivity – few false negativesTPSensitivity = x 100TP + FN
9SPECIFICITY-Accuracy with which the test can confirm the absence of an infectiontest with high specificity – few false positivesused for diagnosing infection in an individualTNSpecificity = X 100TN + FP
10Efficiency - ability of a test to correctly identify - all positives as positivesall negatives as negativesTP + TNEfficiency = X 100TP + FN + TN + FP
11Predictive valuesPPV – identifies ACTUALLY infected individualsTPX 100TP + FPNPV – identifies ACTUAL non infectedTNTN + FN
12ELISA Most common screening test Indirect solid phase enzyme linked immunosorbent assay/ EIAUsed in blood banks/ tertiary labsFourth generation ELISA decreases window periodDISADVANTAGESMany false positivesFew false negativesTime consumingNeeds infrastructure & tech. expertise
13PRINCIPLE OF INDIRECT ELISA SubstrateEnzyme conjugatedAnti-HIV antibody in specimenAntigenOn solid phase
16Comb AIDS NON-REACTIVE INVALID TEST Dot immunoassay for HIV 1&2 using whole blood,serum or plasma.Comb with 8 teeth- Megenta red spotSynthetic& recombinant peptides usedTwo spots-- Control spot & test spot.NON-REACTIVEREACTIVEFor HIV-1 &2INVALID TEST
17TRIDOTHIV 1 – gp 41, gp 120.HIV 2 – gp 36.Highly specific.C12
20INTERPRETATION OF RESULTS HIV EIA CombRapid Visual EIA TestDetection of Antibodies to HIV-1 (includingsubgroups O & C) and HIV-2Sensitivity (100%)Specificity (99.9%)INTERPRETATION OF RESULTSNON-REACTIVEHIV-1HIV-2HIV-1&2REACTIVEINVALID TEST
21SUPPLEMENTAL TESTS 1.Rapid tests. 2.Western blot. 3.Immunoblot. 4.Line immunoassay.WB/IB/LIA: highly specific but Expensive Labour intensive Needs expertise Equivocal/indeterminate results.
22Western Blot for HIV Delineates the antibody profile of reactive serum Used to grade intensity of ab responseQualitativelyQuantitativelyProcedure based on principle of ELISAWB Rotator platformWB strips
23Western blot for HIV antibody gp 36Control bandp 24gp 31gp 41gp 120 & 160
24TESTS DONE IN VCCTC, PPTCT & BLOOD BANK Test – I: HIV Comb / Comb Aids – RSTest – II: Tridot / RetroquicTest – III: EIA CombFOR SURVEILLANCE:BLOOD BANK:Only Test: Microlisa HIV
25STRATEGIES/ALGORITHMS OF HIV TESTING 1.Screening ELISA/Rapid tests – used in strategy I, II, III.2.Supplemental tests – E/R & Western Blot.Strategy I (for transfusion/transplantation safety)one test kit requiredAIA A positive negative
26Strategy/Algorithm II A (for surveillance) 2 test kits required A1 A A Report negativeA2A1 + A A1+ A Report positive Report negative
27Strategy/Algorithm II B (Diagnosis of an individual with AIDS indicator disease symptoms) test kits required A1A A report negativeA2A1+ A A A report positiveA3A1+ A2 – A A1+ A2 - A indeterminate report negative
28Strategy/Algorithm III To detect HIV infection in asymptomatic individuals (VCTCs, PPTCTs) test kits required A1A A Report negativeA2A1+ A A1+ A2 –A3A1+ A2+ A A1+ A2+ A A Report positive indeterminateA1+ A2- A A1+ A2- A Indeterminate report negative
29INDETERMINATE STATUS: Repeat test after 14-28 days INDETERMINATE STATUS: Repeat test after days Results continue to be indeterminate – WB/PCR refer to NRL.EQUIVOCAL WB: Rpt. WB after 2 weeks weeks weeks one year Correlate with high risk behaviour & clinical parameters.
30TESTS TO DETECT ANTIGENS P24 Antigen: Uncomplexed in serum, plasma, CSF, cell culture Indicates Active infection especially in newborn Resolves equivocal WB Window period CNS disease Immune collapse Monitoring response to ART.Method: EIADisadvantages: Expensive Limited sensitivity Failure to detect HIV Failure to detect Ag when complexed with Antibody
31Limitations of antigen detection methods Not reliableExpensiveLimited sensitivity-69% in patients with AIDS,15% in neonatesDetection not possible in patients with high anti p24 antibodyCannot be used as a screening test
32PCR Highly specific test-more than 95% Highly sensitive-infants over 1 monthDetects proviral DNA .Detects both latent viral infection and active viral transcriptipn.Detects viral load.Detects both HIV1 & HIV2.
33PCR AS VIRAL ASSAYS IN INFANTS Counselling for infant feeding & therapeutic intervention.First done at 6 weeks.Not Breast-fed, to say not infected: 2 negative test after 1 month (include 1 at 4 months)Not done as part of PPTCT in India.If symptoms occur at < 18 months: go for viral assays.
34Diagnosing HIV infection in an infant born to HIV positive mother Protocol 1Asymptomatic18 months-ELISANon-reactive ReactiveConditionally consider confirm with a retestNon-infectedRe-testNRHIV Unifected
35PROTOCOL 2 SYMPTOMATIC Early symptoms AIDS Earlier than 12 mon defined symptomsViral assay at 6 weeks same as for earlyWhenever symptoms occur symptomsRetest 1 month laterIf both are reactive considerreactiveELISA at 12 monthsNon reactive ReactiveFollow protocol conditionally consider HIV +veRetest at 18 months retest at 18 monthsNon reactive reactiveHIV UNIFECTED HIV INFECTED
36HIV TESTING POLICY IN PPTCT PARENT: Informed consent of the patient Pre n post test counselling Routine testing with three rapid tests first: highly sensitive test-NR-reported with exception of WP Indeterminate: 1st test reactive, 2nd/3rd NR repeat test after days WB/PCR: For persistent indeterminate cases.INFANT OF HIV + MOTHER, ASYMPTOMATIC: ELISA at 18 months—NR—Retest—NR—uninfected Reactive—consider infected, confirm with retest.INFANT OF HIV + MOTHER, SYMPTOMATIC:ELISA at 12 months—NR—retest NR—uninfected.Reactive—retest R at 18 months—infected.