Breath tests only detect alcohol levels. If the police believe you are impaired by anything other than alcohol, the only way to test for that is by obtaining a blood sample and sending that sample to the Washington State Toxicology Laboratory for testing. Established case law says that drawing a person’s blood is a search that is constitutionally protected, so in order for the police to get your blood sample, they need to get a warrant. In order for a warrant to be valid, it must be supported by probable cause, which means that the police officer must present, under oath, sufficient facts to convince a judge that a crime has occurred, and that evidence of that crime is contained in your blood. It is not enough for the officer to simply state that “I arrested this person and I think they are drunk or high or intoxicated.” The officer needs to provide a factual basis for their suspicion. Details make or break a case, and when an officer omits important details, the warrant can become invalid, which means that the blood sample was obtained by way of illegal search, so the results will not be admissible – no matter what kind of alcohol or drugs the testing shows.
Police can also get your blood if they have an exception to the warrant requirement. If you agree to allow police to take you to a medical professional to draw your blood, you are consenting to the blood draw, and this is a valid search. Do not consent to a blood draw. There are other ways to challenge the admissibility of the blood results, but a faulty warrant is the first line of attack.
The Constitution is not a technicality. Make the officers apply for a warrant if they want to test your blood.