How Errors in DWI Blood Test Procedures Can Give You Strong Defenses in a DWI Case

A blood test result is often the first thing a prosecutor points to in a DWI case to claim a person is guilty of DWI. However, that result is only reliable if DWI blood test procedures are followed and no breaks in the chain of custody occur after the blood sample is collected.  

Our experienced DWI lawyers at Browning & Long, PLLC, are former prosecutors who have handled DWI cases throughout Charlotte and Mecklenburg County for decades. If blood testing played a role in your charge, we understand what the law requires and how to use errors as a foundation of a meaningful defense.

When Do Police Use a Blood Test Instead of a Breath Test?

Under North Carolina’s implied consent laws, you impliedly consent to a breathalyzer or blood test when you are arrested for DWI. While a breathalyzer test is frequently used, the police can decide on a blood test instead. Blood samples are typically taken in these situations: 

• The driver is hospitalized.
• Drug impairment is suspected.
• The driver refuses a breathalyzer.
• A warrant is required because the driver refuses any testing.

DWI Blood Test Procedures: Hospital Draws vs. Police or Forensic Draws

Depending on the circumstances, the police could have blood drawn at a hospital or law enforcement facility. Where blood is collected affects how courts treat it as evidence.

Hospital Blood Draws

When a driver is injured or receiving treatment, medical staff may draw blood for patient care, and the police can sometimes request or subpoena those results. The problem is that hospital nurses and lab techs may not follow the same chain-of-custody standards used in a forensic draw. Prosecutors who want to use that blood at trial must typically show the sample was properly secured and meets DWI blood test procedures and forensic standards.

Police or Forensic Blood Draws

Under N.C. Gen. Stat. § 20-139.1(c), blood must be drawn by a physician, nurse, EMT, or other qualified person with medical training. Because many officers lack that certification, draws are often performed by a registered nurse, with the officer taking possession of the sealed sample afterward. Every handoff from that point must be documented. If an unqualified police officer or other person performs the blood draw, the DWI blood test procedures and evidence can be disputed.

What Is Chain of Custody and Why Does It Matter for Your Defense?

Chain of custody is the documented record of everyone who handled the blood sample from draw to courtroom. When that path breaks down, the evidence may not hold up.

Under G.S. § 20-139.1, each person in the chain must sign a statement confirming they delivered the sample to the next person in essentially the same condition as received. That documentation ties the lab result to the actual defendant. Without it, there's no reliable way to confirm the tested sample was the one taken from you.

The state may introduce a chain of custody statement without calling every witness, but only if it notifies the defendant within 15 business days of receiving the statement and at least 15 business days before trial. You have the right to object. As part of your thorough defense, our skilled DWI lawyers will carefully examine whether those requirements were met and raise a challenge if we can.

Four Ways Our DWI Lawyers Challenge Blood Evidence

Blood testing is more precise than breath testing, but it isn't immune to error. Our attorneys reviewing your blood draw test results generally focus on four areas:

• Collection methods. Was a non-alcoholic swab used to clean the site? Did a qualified professional perform the draw? Were the sample tubes properly preserved? We’ll examine all the DWI blood test procedures for errors in the process and contamination before the sample even reaches the lab.
• Chain-of-custody gaps. Was the sample mislabeled or left unrefrigerated? Are there unexplained gaps in the timeline? Police must account for the blood sample at all times. If they cannot, the chain may be considered broken.
• Lab credentials and procedures. Whether the lab is accredited and whether technicians followed standardized protocols are both open to challenge. Calibration errors and storage failures can compromise results.
• Timing of the draw. The longer the gap between driving and collection, the more likely it is that a driver's BAC has declined. That delay raises legitimate questions about whether the reported number reflects actual impairment at the time of the stop.

In addition, the person taking the blood draw is required to take an additional blood sample that the defendant can have independently tested. If our DWI lawyers believe it would be helpful to your defense, we’ll arrange for your blood sample to be independently tested.

How a Motion to Suppress Can Remove Flawed Blood Evidence

When DWI blood test procedures aren’t followed, or the chain of custody is broken, you have a powerful defense tool: a motion to suppress evidence. If granted, the court excludes the flawed evidence. Without a valid BAC result, the prosecution's case often weakens significantly. 

Grounds for suppression in a North Carolina DWI blood case include:

• Failure to advise of implied consent rights before the draw took place
• An unqualified person performing the blood draw in violation of G.S. 20-139.1(c)
• Improper collection techniques, including the use of an alcohol-based antiseptic, which could have contaminated the draw
• Broken chain of custody, such as missing signatures, mislabeled samples, or unexplained gaps in possession
• Procedural violations in how the state provided notice of the chain of custody statement
• Lab errors, including faulty calibration, improper storage, or unaccredited testing

Challenging blood evidence is just one part of a comprehensive DWI defense strategy. Our knowledgeable DWI lawyers at Browning & Long, PLLC, will scrutinize every aspect of the state’s case against you and fight for the best possible outcome.