Seafarer with solitary, well-functioning kidney - fit for service at sea without restrictions?

A 20-year-old, healthy man, who four years earlier had lost a kidney in a skiing accident, applied for a medical fitness certificate for service on board German flag vessels. Under reference to national and international regulations he was initially turned down, but attained permission to sail on appeal. We discuss the justification of denying persons with a single, well-functioning kidney the opportunity to work at sea, conclude that there is no good reason to refuse a fitness certificate, and propose to change national and international regulations accordingly.