Whole blood samples for faster real-time PCR analysis of thrombophilic mutations in SARS-CoV-2 virus positive patients.

High incidence of thrombosis and venous thromboembolism was reported in patients with COVID-19. In this study, we focused on analysis of thrombophilic mutations performed without a standard DNA extraction step. In one hundred of COVID-19 positive outpatients, real-time PCR for Leiden mutation in the FV gene and G20210A mutation in the FII gene was carried out from DNA extracts and modified whole blood samples, and their cycle threshold (Ct) values were evaluated. In the extracts, healthy homozygotes (wt/wt), heterozygotes (M/wt), and homozygous carriers of Leiden mutation (M/M) provided median Ct values of 18.5, 19.4/22.0, and 20.9. In the whole blood, Ct values were 25.3 (wt/wt), 24.8/27.2 (M/wt), and 26.9 (M/M). Median Ct values for G20210A in the extracts were 19.6 for homozygotes (wt/wt), and 19.7/20.4 for heterozygous carriers. The whole blood samples provided Ct values of 23.9 in healthy homozygotes and 26.3/27.2 in heterozygotes for G20210A mutation. No homozygous subjects for G20210A and no double heterozygotes (for Leiden and G20210A mutations) were found. Despite significant differences in the Ct values, genotyping showed complete result concordance of the DNA extracts and the whole blood samples. The integrity and amplificability of DNA molecules in the whole blood samples during 28 days of deep freezing, interrupted by four cycles of thawing, did not significantly change. In conclusion, we demonstrated a new protocol for the detection of the thrombophilic mutations via real time PCR on the modified whole blood of COVID-19 positive patients. The blood modification was reliable, easy, cheap, and saving costs and turnaround time of the whole laboratory process.

No Inhibitory Effect of Heparinized Blood on Real-Time PCR Analysis of Thrombophilic Mutations.

We compared the efficiency of real-time PCR analysis of FII (c.*97G>A, G20210A) and FV Leiden (c.1601G>A) thrombophilic mutations in the samples obtained from venous blood treated with various anti coagulant agents (EDTA, heparin, and sodium fluoride with potassium oxalate), or from clotted venous blood; one hundred samples of wild-type subjects were tested. Genomic DNA extracts and whole blood specimens modified by 90 °C heating were analysed by real-time PCR analysis; cycle threshold values were subsequently evaluated. Real-time PCR analysis for the FII gene assay performed in DNA extracts from EDTA blood samples revealed a median Ct value of 19.3. Similar Ct values were apparent in the DNA extracts obtained from the heparinized blood and sodium fluoride with potassium oxalatetreated samples: 18.5 and 18.9, respectively. Significantly higher Ct values were found in extracts from clotted blood with medians of 20.6 (tubes with inert separation gel) and 20.5 (tubes without the gel, both P < 0.001). The data on the FV real-time PCR analysis were very comparable to the FII assay. In the modified whole blood, the samples treated with heparin salts showed significantly lower Ct values (P < 0.001) in both assays when compared with the samples with EDTA, sodium fluoride with potassium oxalate, and with the samples with clotted blood. Our results indicate that real-time PCR analyses of thrombophilic mutations were not negatively influenced by the presence of heparin salts in collection tubes. Blood samples with various anticoagulants might be exchangeable for each other when DNA analysis of thrombophilic mutations is required.