Tokuda Hospital Sofia


PCR tests for COVID-19 at Tokuda Hospital detect infection in the "English version" of the virus

03 febuary 2021

Can PCR tests detect COVID-19 infection with the new "English" version of the virus?

Authors: Prof. Dr. Radka Argirova, MD

Dr. Veselina Koleva, Head of Clinical Laboratory

As an RNA virus, the causative agent of COVID-19 is prone to mutations. One of the persistent mutations, popularly known as the "UK variant", spreads extremely fast. It reveals several changes in regions of the gene that encodes the main protein responsible for the entry of the virus into human epithelial cells - the so-called “spike protein”. According to research, these mutations are the cause of higher infectivity - transmission and spread of the virus in the geographical areas where it is confirmed. There are scientific reports on changes that occur mainly in the S gene of the virus proving they have less sensitivity and specificity for diagnostic methods that use only this gene to detect the virus. In these methods, based solely on S-gene determination, it is very likely that the infection will not be detected. At Tokuda Hospital, there are kits that detect regions of two or three genes other than the S gene that have been shown to be more conservative and virus-specific, such as RdRp, ORF1ab, N-, are used to diagnose SARS-CoV-2. This avoids the possibility of false-negative results or skipping the infection. Molecular diagnostics with RT-PCR continues to be the standard in the detection of SARS CoV-2. The sample is taken from the nasopharynx and pharynx, where the virus particles first enter and can be detected at the earliest stage of infection. RT PCR tests have the highest sensitivity and specificity. "The time interval in which viral particles are most likely to be detected is from day 3 after infection to 10-14 days after the appearance of clinical symptoms," experts at Tokuda Hospital say. An alternative to proving the infection are rapid antigen tests, which are also taken from nasopharyngeal secretions. Unlike the PCR test, which detects viral particles, the antigen test proves the presence of a viral envelope protein in the sample. This makes them suitable for rapid orientation in emergencies and for patients with complaints who suspect they have a COVID-19 infection. The recommended time for testing with an antigen test is during the first 7 days after the first symptoms. In the case of complaints with a longer statute of limitations or too soon after risky contact, the result may be false negative.


See more information for all types of tests to prove infection and antibodies:

  • Tests for active COVID-19 infection
  • Tests to detect antibodies after infection
  • Combined tests


See more


Hospital location

51B Nikola Y. Vaptsarov Blvd., Sofia, 1407 (if you drive, the entrance is from Atanas Dukov str.)

The hospital has a parking lot for patients and visitors. The first 30 min. are free of charge, every next hour is 3BGN/hrs.
IMPORTANT! Have in mind that the parking lot is very busy Monday to Friday between 10.00 and 14.00. The hospital team will appreciate if those whose health condition allow, take the drop off option without parking or use other transport means or alternative parking lots in the area.

Public transport:
Buses: №88, 120

Metro lines: You can get off at James Bourchier or Vitosha metro station and walk to the hospital.


From the Central Railway Station

Bus: take bus #305 and get off at Romanian Embassy stop, then transfer to bus #120 to Tokuda Hospital stop.

Metro: Take metro line Nadezda-Lozenetz and get off either at James Bourchier or Vitosha metro station, then walk to the hospital.