I received a p4 letter from nvc I'm in the US 4 the past 29 years but my interview is schedule for April 29 2016 in my birth country port of Spain t

The petitioner either selected consular processing on the petition or you are ineligible for adjustment of status. Not everyone can pursue a green card in the United States. Some individuals are required to pursue an immigrant visa through consular process. You need to consult an attorney before departing the country. Your departure could trigger a bar to admission. You may find yourself stuck outside the country. You can read more about family-based immigration at http://myattorneyusa.com/family-immigration.