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The State must prove a person is 0.08 or above in a chemical test (breath, blood, or urine), to prove their case by the 0.08 standard. 

State needs Consent: A person can refuse a chemical test.  If that person did not voluntarily take the test, it is not admissible.

Voluntariness must be proven by clear and convincing evidence.  The courts consider the following in determing if it is voluntary:

1) claim of authority,
2) show of force - coercive surroundings,
3) threat to seek or obtain a search warrant,
4) officer's deception of identity or purpose,
5) prior unlawful police actions,
6) if Miranda warnings were given,
7) if the defendant was aware of his Fourth Amendment rights,
8) a confession or other cooperation,
9) denial of guilt,
10) defendant's maturity, sophistication, and mental or emotional state.

Mandatory Specimens: An officer (or the State) may force someone to provide a blood or breath specimen if they are arrested for DWI and they have been involved in an accident where another person is seriously injured or may die (or has died).

1) Breath Tests: Breath tests are what the police usually use in a DWI.

For the breath test to be admissible, the State must show:
    a. that the chemicals were properly compounded in the reference solution in the machine,
    b. that the machine was supervised periodically by someone who understood the science (or theory) of the machine, 
    c. the State must have a qualified witness to the result, someone who is qualified to interpret and translate the results in order to get that proof into evidence,
    d. the operator must be certified as an operator of the machine, and have a valid certificate from the DPS (Department of Public Safety),
    e. they must prove that the analysis was done according to the DPS rules.

2) Blood Tests:   The most accurate test is the blood test.

For a blood test to be admissible, the State must show:
a. specimen at the request or order of a peace officer,
b. consented to the withdrawal of the sample,
c. proper person withdrew the blood,
d. sample taken in a sanitary place,
e. place where the sample is taken is/was inspected periodically.

3) Urine Tests: Urine tests have the same requirements as blood.  Urine tests are the least reliable since it tests what is in the urine which may be saved from several hours back (which means it may show what the blood level was hours ago and confuse the results).  Usually, the officer will request the person to empty his bladder 15-20 minutes prior to the urine test. If they don't do so, the test should be challenged.