MINNEAPOLIS  — The Minnesota Court of Appeals on Tuesday reversed the conviction of a suspected drunken driver who pleaded guilty to refusing to submit to a blood test, saying a warrantless search of the man’s blood would have been unconstitutional in his case, so charging him with refusing that test was a fundamental violation of his rights.

The case was sent back to the lower court so the man could withdraw his guilty plea.

The decision could have implications for Minnesota’s test-refusal law.

“If I were teaching police officers today, I’d say, ‘Try to get a warrant every time if you think you need blood,”’ said Joe Daly, professor emeritus at Hamline University School of Law. “Unless you have an exception to the Fourth Amendment, or unless you have permission or a warrant … you just can’t take blood.”

The Ramsey County Attorney’s Office, which prosecuted the case, said it plans to appeal to the state Supreme Court.

Under Minnesota law, it is a crime to refuse to submit to a chemical test of blood, breath or urine under certain conditions, including when a person is under arrest on suspicion of driving while impaired.

The ruling stems from the 2012 arrest of Todd Trahan, who allegedly smelled of alcohol, had trouble standing and was driving with a canceled license because of prior drunken driving convictions. At the jail, authorities alleged, Trahan tampered with a urine test, then refused a blood test.

Trahan was charged with refusal to submit to a chemical test and pleaded guilty but then appealed, arguing that the test-refusal statute as applied to him violated his right to due process because it criminalized his refusal of an unconstitutional search.

The majority of the three-judge appellate panel agreed, finding that Trahan’s case didn’t meet exigent circumstances that would have prevented police from getting a warrant, so a warrantless blood test would have been unconstitutional.

Trahan’s attorney, Cathryn Middlebrook, said she was pleased with the decision.

Judge Kevin Ross dissented.

“But after today’s decision, police should never merely request a blood test, because if they do, upon refusal, not only is no test permitted, but also conviction is far less likely.”

In July, the appeals court affirmed a law that makes it a crime for someone to refuse a breath test when arrested for drunken driving, but one judge signaled at the time that there could be an issue with the law as it relates to blood or urine tests.