identify "consecutive dates"

AbbasZavar22

I have patients' data set and I have to identify two "consecutive dates" of lab test results dates which are between 90-700 days.
Each patient has several lab test results, how can I compare all two dates together and find the consecutive dates?


Patient_ID                               Performed_date     TestResult

1.00100000023498E15	Thu May 28  2015	54.0
1.00100000023498E15	Thu Sep 26  2013	59.0
1.00100000023498E15	Tue Oct 28  2014	53.0
1.00100000023498E15	Wed May 06  2015	54.0
1.00100000023498E15	Tue May 05  2015	55.0
1.00100000023498E15	Fri May 01  2015	48.0