The Ministry of Health said this quality assurance check was in line with Laboratory Standard Operating Procedures and protocols as well as international best practices.
The results, which pushed the number of positive cases to 40, were therefore being considered as interim.
The ministry yesterday tested 672 people raising the number to 8 314. All 208 cases from Bulawayo were negative but results for 261 cases in Harare were still pending.
Zimbabwe has so far recorded four deaths and five recoveries.
A national lockdown declared by the government ends on Sunday.