Sure, you can always refuse to take a breathalyzer test, but it may just make things worse.
In Missouri, a refusal to take a breathalyzer test can result in a license suspension for 1 year. In addition, if you take your case to trial but have refused the breathalyzer test, the jury may use this against you.
Finally, 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.
Thus, even though you may legally refuse a breathalyzer test, it may be in vein.