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s Indian Journal of Medical Microbiology 39 (2021) S1–S133 Conclusions:hence, screening for corona virus is must before proceeding with surgery to protect,surgeon, healthcare workers, and patients. https://doi.org/10.1016/j.ijmmb.2021.08.214 A STUDY ON PREVALENCE OF COVID 19 IGG ANTIBODY INCOVID19 RTPCR POSITIVE SYMPTOMATIC, ASYMPTOMATIC AND COVID 19 RTPCR NEGATIVE HEALTHCARE WORKERS IN A TERTIARY CARE CENTER IN SOUTH INDIA D. Therese Mary, M. Suganthi, Usha Krishnan. Government Kilpauk Medical College Background:In the year 2019 a new corona virus named as severe acute respiratory syndrome coronavirus 2(SARS -CoV-2) originated from Wuhan, Hubei province, China has led to an outbreak of severe acute respiratory syndrome leading to sudden death in some of the individuals infected with this particular virus. Laboratory diagnosis is made by RTPCR to detect viral nucleic acid or Rapid antigen test. Detection of IgM and IgG antibody gives clue on whether the infection occurred is recent or past. This in turn will help in epidemiological studies. Hence this study was designed to find out the prevalence of COVID-19 IgG antibodies in Laboratory confirmed COVID19 positive symptomatic, asymptomatic and RTPCR negative subjects. Methods:The type of study is cross-sectional study involving 3 different groups of subjects and the study period is 3 months from the date of Institutional ethics committee approval. Sample size is 180 with equal distribution among study group. Blood sample was collected under strict aseptic precautions and serum was separated. Sera were tested by ELISA test to detect the presence of COVID19 IgG antibody. Results:The covid-19 IgG antibody detected from the subjects among the three groups will be compared by using t test. The statistical significance was set at p<0.05. Conclusions:This study will throw light on immune response of the individuals to covid-19 infection and serve as a tool in epidemiological studies. Further studies will elucidate whether the antibody will prevent reinfection. https://doi.org/10.1016/j.ijmmb.2021.08.212 S62 INCONCLUSIVES: THE DIAGNOSTIC DILEMMA OF COVID-19 Jai Ranjan, Baijayantimala Mishra, Swarnatrisha Saha, Akshatha Ravindra, Monalisa Mohanty, Srujana Mohanty, Bijayini Behera, Vinaykumar Hallur, Ashoka Mahapatra. Department of Microbiology, AIIMS, Bhubaneswar Background:COVID-19 RT-PCR kits of various manufacturers categorize certain samples as inconclusive and repeat testing or re-sampling is advised in those cases to ascertain positivity or a negative result. This is of paramount importance because a definite result helps in effective implementation of public health measures, leading to implicit containment. Our study aims to ascertain criteria through which the inconclusive can be definitively categorized as either positive or negative. This will be of help in conserving manpower and resources which are utilized in re -testing of patients with inconclusive RT-PCR result. Methods:Hundred samples which were inconclusive (IC) as per Q-Line Covid-19 RT-PCR kit from 1st September, 2020 to 31st October, 2020 were included in the study. These were classified into 4 groups based on Ct value of N gene; namely A (<25; 3 samples), B (25-30.9; 31), C (31-34; 62) and D (>34; 4) and were tested by NIV kit. RNA extracts of these samples were run through ICMR-NIV rRT-PCR screening and confirmatory assay to ascertain a criteria with which inconclusives can be definitively reported as either positive or negative. Results:Majority (62%) of IC samples were in group C (Ct 31-34) followed by 31% in group B, 4% in D and 3% in group A (<25). Confirmed positivity by NIV kit was 100% in group A and 51.6%, 20.96% and 25% respectively in B, C & D groups.29% of group B and 24% group C samples remained inconclusive by NIV kit. Majority of confirmed negatives were found in group D (75%), followed by group C (54.83%). Conclusions:All inconclusive samples with Ct values of N gene less than 25 were positive with ICMR -NIV kit, whereas >50% of samples of Ct >30 became negative. Repeat sampling could be avoided in 76% cases by following strategy of repeat testing in NIV kit. https://doi.org/10.1016/j.ijmmb.2021.08.213 INTERLABORATORY COMPARISON IN COVID TESTING: AN EXPERIENCE FORM ICMR DESIGNATED LABORATORY Kavita Meena, Vikas Manchanda, Oves Siddiqui, Sonal Saxena. MAMC Background:In resource-constrained settings, the majority of laboratories are not accredited to international standards and may only be partially implementing elements of a QMS. ICMR started an Inter -Laboratory Quality Control (ILQC) program for Covid-19 testing. Under this program, RT-PCR testing laboratories across the country send 10 Covid testing samples; five positive and five negative, quarterly to the assigned State Quality Control (SQCs) laboratories for ILQC testing. MAMC Covid-19 laboratory is one of the SQCs laboratory which receives samples for testing. We are presenting here ILQC results and experience of MAMC SQCs Laboratory. Methods:In the duration from July through to November 2020 a total of 445 anonymized samples were received from 24 various public and private linked laboratories. These samples were processed by RT -PCR tests as per NIV protocol. Results were uploaded on the ICMR QC/QA portal to keep pace with the latest technical developments and to synchronize with the International Standards. ICMR QC/QA portal generated a final report stating concordance of the results to individual laboratories. Results: Among 445 samples, three samples were rejected as leaked. A total of 442 samples tested. Of these samples, 317 Covid testing samples results are available till date from ICMR which were received in 25 different batches from 18 laboratories. Out of total 317 samples, 308 samples (97%) showed concordant results and 09 were discordant. A total of 19 sample batches showed complete concordance. Only 6 batches from different laboratories showed disagreement. Of these laboratories two laboratories were public and four private laboratories. A total of 12 laboratories had 100% concordance.