(Adds details, comment from company)
ZURICH, Aug 28 (Reuters) - Roche diagnostics head Roland Diggelmann is resigning as of Sept. 30, ending a 10-year stint at the Swiss drugmaker and for now leaving the business with 12.1 billion Swiss francs ($12.15 billion) in sales without a permanent leader.
Michael Heuer, head of Roche Diagnostics for Europe, the Middle East, Africa, and Latin America, will take over on an interim basis until a replacement is named, Roche said on Tuesday.
Diggelmann, 51, arrived at Roche from the medtech industry in 2008, having held executive roles at Swiss hip maker Sulzer Medica before and after it was purchased by Zimmer.
Since 2012 he has led Roche's diagnostics unit, which makes equipment and sophisticated tests for diseases but has also been held back in recent years by its sluggish diabetes business.
Diagnostics accounts for more than 20 percent of Roche's annual sales, and is seen as playing an increasingly important role in tests to determine the effectiveness of cancer immunotherapy.
Roche said Diggelmann would "pursue his career outside of the company". Diggelmann could not immediately be reached for comment.
"I wish him all the best for the future," Chief Executive Severin Schwan said in a statement.
For years, Diggelmann has been Roche's point person in countering persistent suggestions the company would unload diagnostics' diabetes business, even as others including Johnson & Johnson and Bayer exited amid increased competition and public-sector medical insurers' steady pressure to cut reimbursements.
A two-decade Roche veteran, Heuer was a longtime Boehringer Mannheim employee before Roche bought the German diagnostics-and-drug company in 1998.
Since then, the trained chemist has held roles in sales, marketing and product development in Germany, Austria and the United States. He will become a member of the corporate executive committee.
"Michael is a very respected leader with a wealth of experience in diagnostics," Schwan said.
$1 = 0.9957 Swiss francs Reporting by John Miller; Editing by Michael Shields