After graduating, he turned professional as a sponsored athlete with Nike. Rankin trained and raced throughout the US and Europe. On 11 August 2007 he won the Emsley Carr Mile in Manchester, England in a personal best time of 3:54.24, A year later in 2008, at the time of the United States Olympic Trials, he was diagnosed with focal segmental glomerulosclerosis (FSGS), although his official diagnosis didn't come about until the end of 2008. FSGS is estimated to occur in 2-3 persons per million, with males and African peoples at higher risk. Later in 2011, Rankin underwent an experimental stem cell surgery to reverse his disease.