COVID-19 Tanısında Laboratuvar Testleri

Koronavirüs hastalığı 2019 (coronavirus disease 2019, COVID-19) için rutin mikrobiyolojik tanıda altın standart, solunum yolu örneklerinde viral RNA’nın gerçek zamanlı revers-transkriptaz polimeraz zincir reaksiyonu (RT-PCR) ile gösterilmesidir. Hasta serumunda şiddetli akut solunum yolu sendromu koronavirüsü 2 (severe acute respiratory syndrome coronavirus 2, SARS-CoV-2)’ye spesifik olan IgG ve IgM antikorların gösterilmesi de ek tanısal testlerdir. Virüs atılımının klinik bulgulardan birkaç gün öncesinden başladığı ve bu yüzden semptomların başlamasından 2-3 gün öncesinden itibaren klinik dönem boyunca virus RNA’sının solunum yollarında tespit edilebileceği bilinmektedir. Bronkoalveolar lavaj ve trakeal aspirat gibi alt solunum yolu örneklerinde viral yük daha fazla olduğundan PCR pozitiflik oranı nazofaringeal örneklere kıyasla daha yüksektir. Zaman alıcı ve pahalı olan doğrulayıcı PCR testleri, özel ekipman ve deneyimli personel gerektirir. Antikor testleri ise basit, hızlı sonuç verebilen, ciddi ekipman gerektirmeyen ve hemen her laboratuvarda yapılabilen testlerdir. Nispeten ucuz olan kramotografik hızlı kart testlerle parmak ucundan alınan 2-3 damla kanla, hasta başında bile yapılabilir. COVID-19 geçiren kişilerde hastalığın 7-10. gününden itibaren oluşan antikorlar sebebiyle, bu testler daha geç bir zamanda kullanılabilir. Hızlı antikor kart testleri ortalama bir özgüllük ve duyarlılığa sahipken, mikroELISA ile çalışılan antikor testlerinin duyarlılık ve spesivitesi ise daha yüksektir.

Anahtar Kelimeler:

COVID-19, PCR, antikor, seroloji

Laboratory Tests in the Diagnosis of COVID-19

The gold standard for routine microbiological diagnosis of coronavirus disease 2019 (COVID-19) is quantitation of viral RNA in respiratory specimens by reverse-transcription polymerase chain reaction (RT-PCR). Detecting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific IgM and IgG antibodies in patient sera are additional diagnostic tests. It has been known that virus release begins a few days before clinical signs appear, and therefore, beginning from 2-3 days before the manifestation of clinical symptoms, virus RNA can be detected in the respiratory tract during the symptomatic period of the disease. Since the viral load is higher in lower respiratory tract samples such as bronchoalveolar lavage and tracheal aspirate, PCR positivity rate might be found higher compared to nasopharyngeal samples. Confirmatory PCR tests require specific equipment and trained personnel, and they are also time-consuming and costly. Antibody assays are simple, faster tests, do not require much equipment and applicable in any laboratory. They can even be performed with 2-3 drops of blood collected from the finger tip of patients using relatively inexpensive chromatographic-rapid tests. These tests can be used in the later period of the disease since specific antibodies appear on the 7-10th day of clinical signs in patients with COVID-19. Rapid antibody card tests have an average specificity and sensitivity, while antibody tests using microELISA have higher sensitivity and specificity.

Keywords:

COVID-19, PCR, antibody, serology,

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