Moscow’s health department has warned the city’s clinics that many coronavirus tests return false negative results, the Kommersant business daily reported Friday.

A new study this week placed the accuracy of Russia’s Covid-19 tests at 70% to 80%, with the rest being false negatives. Medical experts have raised concerns about the quality of testing in Russia, citing the country’s low infection rates compared with other European nations with smaller populations.

“Negative results for Covid-19 swabs in patients with signs of respiratory disease don’t completely rule out coronavirus infection and a rapid development of complications,” Kommersant quoted the Moscow health department’s letter as saying.

“Therefore, there are high risks of developing severe forms of the disease” caused by coronavirus, department chief Alexei Khripunov’s letter to the heads of primary health care providers warns.

Patients developed complications as rapidly as within a few hours, Khripunov’s letter states, adding that they were more common within three to five days of infection.

It advises doctors to send patients who develop complications to undergo CT scans, which it says are the “only reliable diagnostic test” for coronavirus.

The city’s doctors have been permitted to treat all pneumonia patients as potential coronavirus patients because the fast-spreading virus often causes pneumonia. 

Russian doctors will also be able to diagnose patients with coronavirus without running lab tests, Health Minister Mikhail Murashko said Thursday. He noted that the “course of the disease is sometimes so quick that it has a distinct clinical picture.” 

Russia is currently the world’s 17th-most affected country with 11,917 officially reported coronavirus cases as of Friday.