The WHO said it had asked the maker for a "root cause analysis".
China's BGI Genomics said on Wednesday its diagnostic coronavirus testing kit has "relatively high accuracy", a day after Sweden said about 3,700 people received false positive results due to a fault in the company's product.
The WHO, which has approved the tests for emergency use, said in reply to a Reuters query: "WHO was notified and has activated the complaint procedure for in vitro diagnostics ... to gauge if the observed irregularities were due to the way the test was used.
"Specifically, WHO has contacted the manufacturer and requested a root cause analysis... We are continuing the work with BGI to determine if further action is required," it said.
(Reporting by Stephanie Nebehay in Geneva, Roxanne Liu in Beijing and Miyoung Kim in Seoul; writing by Stephanie Nebehay; ; editing by John Stonestreet)