Inconclusives: The diagnostic dilemma of COVID-19

ABSTRACT

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 im- portance because a definite result helps in effective implementation of public health measures, leading to implicit con- tainment. 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 pa- tients 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 sam- ples were run through ICMR-NIV rRT-PCR screening and confirmatory assay to ascertain a criteria with which inconclu- sives 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.