The Colchester Regional Hospital says results from tests run from June 4 to 6 may be inaccurate after one of its two chemistry analyzers broke down.
The hospital tests roughly 140 samples per day using the machines.
But Manoj Vohra, vice-president of medicine at Colchester East Hants Health Authority, says there's no way of knowing precisely how many results are incorrect.
Vohra apologized for the malfunction.
"While the malfunction may have resulted in only a small number of inaccurate results, the fact is we can't be certain about results for this period of time, and we are erring on this side of caution," Vohra said in a statement Tuesday.
"We are sorry that this has happened."
Patients whose results may have been affected are being notified via letters and are encouraged to follow up with their doctors to see if more tests are required.