According to anti-SARS-CoV-2 seroresponse in patients with COVID-19 from Croatia, we emphasised the issue of different serological tests and need for combining diagnostic methods for COVID-19 diagnosis. Anti-SARS-CoV-2 IgA and IgG ELISA and IgM/IgG immunochromatographic assay (ICA) were used for testing 60 sera from 21 patients (6 with severe, 10 moderate, and 5 with mild disease). The main clinical, demographic, and haemato-biochemical data were analysed. The most common symptoms were cough (95.2%), fever (90.5%), and fatigue and shortness of breath (42.9%). Pulmonary opacities showed 76.2% of patients. Within the first 7 days of illness, seropositivity for ELISA IgA and IgG was 42.9% and 7.1%, and for ICA IgM and IgG 25% and 10.7%, respectively. From day 8 after onset, ELISA IgA and IgG seropositivity was 90.6% and 68.8%, and for ICA IgM and IgG 84.4% and 75%, respectively. In general, sensitivity for ELISA IgA and IgG was 68.3% and 40%, and for ICA IgM and IgG 56.7% and 45.0%, respectively. The anti-SARS-CoV-2 antibody distributions by each method were statistically different (ICA IgM vs. IgG, p = 0.016; ELISA IgG vs. IgA, p < 0.001). Antibody response in COVID-19 varies and depends on the time the serum is taken, on the severity of disease, and on the type of test used. IgM and IgA antibodies as early-stage disease markers are comparable, although they cannot replace each other. Simultaneous IgM/IgG/IgA anti-SARS-CoV-2 antibody testing followed by the confirmation of positive findings with another test in a two-tier testing is recommended.

根据来自克罗地亚的 COVID-19 患者的抗 SARS-CoV-2 血清反应，我们强调了不同血清学检测的问题以及结合诊断方法进行 COVID-19 诊断的必要性。采用抗 SARS-CoV-2 IgA 和 IgG ELISA 以及 IgM/IgG 免疫层析测定 (ICA) 检测了 21 名患者的 60 份血清（6 名重度患者、10 名中度患者、5 名轻症患者）。分析了主要的临床、人口统计学和血液生化数据。最常见的症状是咳嗽（95.2%）、发烧（90.5%）、疲劳和气短（42.9%）。 76.2% 的患者出现肺部混浊。在患病的前 7 天内，ELISA IgA 和 IgG 的血清阳性率为 42.9% 和 7.1%，ICA IgM 和 IgG 的血清阳性率分别为 25% 和 10.7%。从发病后第8天起，ELISA IgA和IgG血清阳性率为90.6%和68.8%，ICA IgM和IgG血清阳性率分别为84.4%和75%。一般来说，ELISA IgA 和 IgG 的灵敏度分别为 68.3% 和 40%，ICA IgM 和 IgG 的灵敏度分别为 56.7% 和 45.0%。每种方法的抗 SARS-CoV-2 抗体分布存在统计学差异（ICA IgM 与 IgG， p = 0.016；ELISA IgG 与 IgA， p < 0.001）。 COVID-19 中的抗体反应各不相同，具体取决于血清的采集时间、疾病的严重程度以及所用测试的类型。 IgM 和 IgA 抗体作为早期疾病标志物具有可比性，但不能相互替代。建议同时进行 IgM/IgG/IgA 抗 SARS-CoV-2 抗体检测，然后在两级检测中通过另一项检测确认阳性结果。