Blood evidence can become the centerpiece of a Tennessee DUI case when a breath test is unavailable, drugs are suspected, a crash sends the driver to a hospital, or police obtain a warrant for a sample. A laboratory number can look definitive on paper, but the legal and scientific questions begin long before the result appears in a report: why the blood was drawn, who drew it, how it was stored, what testing method was used, and whether the result actually reflects the driver’s condition at the time of operation.
Kevin Kennedy represents people facing blood-test DUI charges in Nashville and Middle Tennessee. These cases are often won or lost through details that are not visible from the BAC or toxicology number alone. A careful defense follows the sample from the traffic stop through the laboratory and tests every link in that chain.
How Blood Testing Fits Into a Tennessee DUI Case
Tenn. Code Ann. § 55-10-401 prohibits driving or being in physical control while impaired and also creates a per se alcohol offense at 0.08% or more for ordinary drivers. Blood testing may be used to establish alcohol concentration, drug content, or both.
Section 55-10-406 governs requests for breath and blood testing in DUI investigations. Depending on the facts, a blood sample may be obtained through consent, a search warrant, or another constitutionally valid basis recognized by Tennessee law.
A Blood Draw Is a Search
Taking blood is a significant bodily intrusion. The defense should identify the legal authority for the draw rather than assuming the sample was valid because a nurse or phlebotomist collected it.
When police rely on a warrant, the warrant affidavit should be reviewed for probable cause, timing, accuracy, and whether the warrant actually authorized the sample that was taken. If officers claim consent, the circumstances surrounding that consent matter, including what the driver was told and whether the consent was voluntary.
Hospital Blood and Forensic Blood Are Not Always the Same
A hospital may draw blood for medical treatment while law enforcement separately seeks a forensic sample. Those two samples can be collected at different times, tested by different laboratories, and analyzed for different purposes.
Hospital testing may use serum or plasma rather than whole blood, and clinical screening methods are not always identical to forensic testing. The defense should determine exactly what specimen was tested and what the reported number means before treating two different records as interchangeable.
Chain of Custody Matters
A forensic blood kit typically passes through several hands: the person who collects the sample, the officer who takes custody, an evidence or property system, a courier or shipment process, and laboratory personnel. Each transfer should be documented.
The defense should review seals, labels, dates, storage conditions, submission forms, laboratory accession records, and any unexplained gaps. A chain-of-custody issue does not automatically exclude evidence, but it can affect reliability and admissibility depending on the facts.
Timing Can Change the Meaning of the Result
A blood sample is often drawn well after the vehicle stopped moving. Alcohol concentration can rise or fall during that interval depending on when drinking occurred, absorption, food intake, metabolism, and the time of the last drink.
A later blood result does not automatically establish the exact concentration at the time of driving. When the State uses retrograde extrapolation or other expert testimony to estimate an earlier concentration, the assumptions behind that opinion should be examined closely.
Drug Toxicology Requires Interpretation
When blood testing identifies marijuana, prescription medication, opioids, stimulants, or other drugs, the laboratory result may establish presence without establishing impairment. Many substances do not have a Tennessee per se concentration comparable to alcohol’s 0.08% rule.
The defense should compare the drug level, active versus inactive metabolites, prescribed dosage, timing of ingestion, tolerance, officer observations, and driving behavior. A toxicology result should be interpreted scientifically rather than treated as a verdict.
Testing Method and Laboratory Records
A complete review may include calibration records, quality-control data, chromatograms, analyst notes, instrument maintenance, proficiency information, and the laboratory’s standard operating procedures. These materials can show whether the reported result was produced according to accepted methods.
Section 55-10-408 addresses testing of samples procured under § 55-10-406. Even when the statute permits testing without a second warrant, the defense can still examine whether the sample itself was lawfully obtained and whether the laboratory result is reliable.
Independent Testing and Preservation Issues
Blood is physical evidence that may permit retesting if enough sample remains. In an appropriate case, an independent laboratory can test the retained sample or review the State’s analytical data.
The defense should determine how much sample remains, whether it was properly preserved, and whether the State followed procedures that allow meaningful review.
How Kevin Kennedy Defends Blood-Test DUI Cases
Kevin begins with the legal basis for the blood draw and then follows the sample chronologically through collection, storage, transport, and testing. He compares that evidence with body-worn camera footage, medical records, the traffic-stop timeline, field sobriety evidence, and the driver’s actual behavior.
That approach can reveal whether the State has a strong scientific case or merely a laboratory number surrounded by unanswered questions. If you are charged with DUI involving a blood test in Nashville or Middle Tennessee, contact Kevin Kennedy Law Firm for a free, confidential consultation.
Legal references: Tenn. Code Ann. §§ 55-10-401, 55-10-406, and 55-10-408. This page is general information, not legal advice.