WALTHAM, Mass. (AP) — Medical diagnostics company Alere said CEO Ron Zwanziger, its top scientific officer and a senior vice president of research and development all have resigned, effective immediately.

Alere makes tests that help diagnose heart disease and risk factors for it like cholesterol levels as well as tests for respiratory infections. The Waltham, Massachusetts, company has a site in Scarborough.

It gave no reason for the leadership turnover in a Tuesday morning statement announcing the moves.

Alere Inc. said Chief Operating Officer Namal Nawana will serve as an interim CEO while the company searches for a permanent replacement for Zwanziger, who had led the company since its inception in May 2001. He also had served as chairman from 2001 until May.

David Scott also had served as chief scientific officer since the company’s inception. Jerry McAleer had served as senior vice president of research and development since July 2010 and had been a company vice president since its inception.

Nawana, a former Johnson & Johnson executive, joined Alere as chief operating officer in December 2012.

Its shares were steady at $37.42 in premarket trading Tuesday. Company shares have risen about 3.4 percent so far this year.