After a field sobriety test, the police may arrest you based on those results. If so, they'll then administer a breathalyzer test to measure your Blood Alcohol Concentration (BAC). Or the police may take you to a police station or other authorized location for a blood test to measure your BAC. If you refuse either test, the police can get a warrant for a blood test. The legal BAC limit in Texas is .08% or .04% if you have a commercial license.
It's important to remember that a BAC test of .08% or over does not mean you are guilty of DWI. Both breath and blood tests can be subject to mechanical issues, inaccurate calibration, or even poor test administration. These are highly technical assessments, requiring specific knowledge about breathalyzers and blood testing to understand if the police or lab technician performed the tests correctly.
RECOMMENDATION: You need an attorney with experience attacking police BAC tests and extensive knowledge of the science and technical requirements behind breath and blood tests. Hire an attorney with technical DWI testing training and expertise.