Case Study: Rapid Test Evaluation IgM/IgG (LAMBRA) FOR COVID19 vs RT-PCR PROTOCOL

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Published on Apr 20th, 2020

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INTRODUCTION

Due to the current pandemic, it’s necessary to adopt analytical methods which allow the classification of the patients in a fast and effective way. On their own conventional methods are not enough to deliver results as quickly as the essential emergency decisions need to be made. Therefore, the serological tests are a valid choice. Although the different providers give sensitive and specific data, the scientific communities recommend the requirement to perform local evaluations.

The trial evaluations that are been followed are similar protocols to employers of other companies and authors.

METHODOLOGY

For the fulfilment of this evaluation, serological samples have been collected from patients confirmed positive with COVID19 by PCR in real time (RT-PCR). Likewise, serological samples are collected from patients with negative results for the same technical analysis. Due to the technique been validated for complete blood (capillary blood), serum and plasma, it’s preferred to choose serum, because of its ease to handle the samples and the minimization and exposure of risk while the sample is being taken. It has been ensured that the serum sample used is taken as close in time as the RT-PCR.

The test is performed following the recommendation from the manufacturer. 5μL of serum is applied and 2 drops of buffer solution. The result can be read within 2 – 10 minutes. To avoid any bias, the performance is done no knowing if the patients are positive or negative.

The technique used, lateral flow immunochromatography, allows the detection of both antibodies, making evident the immunological response to infection. The result of the test is analyzed against IgM and IgG separately and they are analyzed in combination as well. The data is transferred to a chart and statistically processed.

Results

IgG

Sensitivity: 0.8333; Specificity: 0.8421

Chi-squared Test: 0.000

IgM

Sensitivity: 0.733*; Specificity: 0.8421

Chi-squared Test: 0.000

Test

Sensitivity: 0.833; Specificity: 0.8421

Chi-squared Test: 0.000

Conclusion

The use of this tests is a valid choice if certain circumstances are followed. In the same way as other tests, there are limitations of use and the circumstances of their application can explain the obtained results. The sensitivity and specificity found are within the acceptable limits. One of the limitations of these tests is the required time to have an immunological response.

The samples are taken following sufficient time from when the symptoms appear to show this fact, however, the lack of result in some cases could be explained due to the sample been collected without sufficient time having passed. This could be the origin of the sensitive results for IgM (*).

The statistical analysis carried out shows the relationship between the two observations, which it would agree with the result of the test.

To sum up, the technique is valid if it is taken timely and following symptoms for at least five days. Its use is recommended to narrow down patients who have to go to emergencies.

The rest of the indications must be evaluated in each particular case, taking into account

local aspects and the availability of other tests.

Dr. Francisco Javier Mérida De la Torre

Jefe de Servicio de Laboratorio Clínico.

AGS Serranía de Málaga

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