It depends. You can always refuse a breathalyzer test, but it could make a bad situation worse.
In Missouri, a breathalyzer refusal can result in a license suspension for 1 year. The prosecution will also use this fact against you if your case goes to trial.
Even if you refuse, the officer can still get a warrant to have your blood drawn. Some counties and municipalities in Missouri have even created laws allowing officers to draw your blood without your permission or a warrant.
The constitutionality of officers taking your blood without your permission is still up in the air, as the Missouri Supreme Court has yet to rule on the issue. We should have an answer this fall.
Thus, don’t think you are out of the woods just because you refused the breathalyzer.