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The cost of PCR coronavirus tests has been capped at Dh50, the Ministry of Health and Prevention said on Monday.
Clinics cannot charge more than that amount and results must be delivered within 24 hours.
The previous price limit was Dh65 in Abu Dhabi and Dh150 in Dubai, with rules differing in the other emirates.
The change comes into effect on Tuesday, August 31.
On Tuesday, clinics in Dubai were still charging Dh150. Dubai's authorities, which have set out separate coronavirus rules in recent months, were asked for clarification.
PCR tests and rapid results have been crucial to getting workplaces, schools and public events back on track.
The maximum price has been cut several times by the authorities to ensure it is affordable across the country. Free tests for pupils and employees in the workplace are common.
On Monday, the authorities said tests for all pupils in Abu Dhabi would be free throughout September. Tests for the 2022 Fifa World Cup Qatar qualifier between UAE and Lebanon, at Zabeel stadium on Thursday, are also free.