By Chandini Monnappa and Shanima A

(Reuters) - British engineering company Smiths Group upgraded its annual organic revenue growth outlook on Wednesday after demand for its next generation scanning and explosives detectors drove first-quarter revenue higher, sending shares to a record high.

Group organic revenue for the first quarter was up 15.8%, boosted by its detection unit, which accounts for 28% of the group's total revenue.

"We expect the rollout of our advanced threat detection systems to continue, the rollouts at airports are not even 50% through and we are seeing strong benefit from it," CFO Clare Scherrer told Reuters in an interview.

Smiths expects full-year organic revenue growth of 5%-7%, up from its previous forecast of 4%-6%, and anticipates its operating profit margin to increase by 0.40 to 0.60 percentage points.

Early on Wednesday, shares soared 21% to a record high of 1,845 pence, recovering from a selloff that meant they were down about 14% this year by Tuesday's close.

We consider this an impressive update, which should be clearly positive to a share price that has been languishing, analysts at Stifel said in a note.

Stifel also said Smiths looked well-placed for new geopolitical realities due to factors such as its limited presence in China.

Scherrer said in the U.S, a region that accounts for 45% of the company's annual sales, demand from safety and security sectors were high.

Smiths is also resuming its share buyback programme and has increased the amount to 150 million pounds($191.03 million) from 100 million pounds.

($1 = 0.7852 pounds)

(This story has been corrected to clarify that the group's revenue grew by 15.8%, not the unit's revenue, in paragraph 2)

(Reporting by Chandini Monnappa and Shanima A in Bengaluru; Editing by Subhranshu Sahu, Janane Venkatraman and Barbara Lewis)