A blood test result in a Montana DUI case is challenged by following the sample from the needle to the report: who drew it, how the site was cleaned, what tube it went into, how it was sealed and labeled, who held it, which laboratory analyzed it, and what the reported number measures. Montana law sets a rule for nearly every one of those steps. This page expands the blood test section of our Montana DUI defenses page and is part of our Montana DUI Guide.
When Blood Is Used Instead of Breath
An officer may designate which test is given (MCA § 61-8-1016(2)(b)). Blood is used when drugs are suspected, because the statute provides for breath testing only for alcohol (MCA § 61-8-1016(1)(a)), and it is also used after some crashes or when a breath sample cannot be obtained. After a refusal, an officer may apply for a search warrant for a blood or oral fluid sample (MCA § 61-8-1016(4)(b)). How the State came to have your blood, by consent, by warrant, or through a hospital, shapes which of the challenges below apply. See test refusal and implied consent.
The Collection Rules
| Step | What the law requires | Source |
|---|---|---|
| Who may draw | Only a licensed physician, registered nurse, or other qualified person acting under the supervision and direction of a physician or registered nurse | MCA § 61-8-1019(1) |
| The request | Samples are collected upon written request of a peace officer or officer of the court | ARM 23.4.220(1) |
| Cleaning the skin | An aqueous solution of a nonvolatile antiseptic. Alcohol phenolic solution may not be used | ARM 23.4.220(2) |
| The container | Clean and dry, capped or stoppered, sealed, and marked with the subject's name, the date and time of collection, and a signed and dated evidence seal | ARM 23.4.220(3) |
| The tube | An approved tube containing a preservative (sodium fluoride or its equivalent) and an anticoagulant (potassium oxalate or its equivalent) | ARM 23.4.220(6) |
| The volume | Enough for accurate and repeatable analyses. A sample below the required volume will not be analyzed | ARM 23.4.220(4) |
| The witness | When possible, the requesting officer observes the collection so the officer can attest to the sample's authenticity | ARM 23.4.220(7) |
| The laboratory | Operated or certified by the Department of Justice, or exempt from certification under its rules | MCA § 61-8-1018(1)(b)(ii) |
The Montana Supreme Court has said, in the breath test setting, that a DUI defendant "deserves the procedural safeguards contained in the administrative rules to ensure the accuracy of such highly relevant evidence" (State v. Frickey, 2006 MT 122, ¶ 18). The collection rule for blood sits in the same chapter of the administrative rules. How a court treats a particular departure from it is decided case by case.
Chain of Custody
A blood sample is drawn in one place and analyzed in another, some time later. The standard for linking the two comes from State v. Weeks, 270 Mont. 63, 891 P.2d 477 (1995), a case that was not a DUI but involved blood samples shipped between laboratories. The Court said:
- the State must make a prima facie showing of a continuous chain of custody and that there was no substantial change in the evidence;
- the burden then shifts to the defense to show that the evidence was tampered with while in the State's custody;
- the State does not have to show it had physical possession at all times, since evidence is mailed and handled by clerks and technicians;
- the State does not have to call every person who handled the sample.
In Weeks the samples had been sent to the wrong laboratory first, and the chain still held because the documentation accounted for each transfer and the seals were intact. That is a fair picture of how these challenges go. A missing signature or a gap in the log is worth raising. Speculation that something could have happened is not enough.
The Laboratory and the Analyst
A blood report is admissible if the sample was analyzed in a laboratory operated or certified by the Department of Justice, or one exempt from certification under the department's rules (MCA § 61-8-1018(1)(b)(ii)). The defense is entitled to the results of scientific tests and the reports of experts who examined the evidence (MCA § 46-15-322(1)(c)), and to full information concerning any test given at an officer's direction (MCA § 61-8-1019(3)).
In practice that means asking for the complete laboratory file, not only the one-page report: the request form, the custody log, the method used, the calibration and control results for the run that included your sample, and the analyst's notes. This page does not describe the laboratory's methods, because the file in your case is the reliable source for them.
Who presents the result matters too. In State v. Clark, 1998 MT 221, 290 Mont. 479, the Court held that the portion of Montana Rule of Evidence 803(8) that then allowed written state crime lab reports into evidence violated the confrontation and due process guarantees of the Montana Constitution (¶¶ 25, 30). Whether to require the analyst in person is a tactical decision to make with your lawyer.
What the Number Measures, and When
Alcohol. The per se offense requires an alcohol concentration of 0.08 or more, defined for blood as grams of alcohol per 100 milliliters of blood (MCA §§ 61-8-1001(3), 61-8-1002(1)(b)). The statutory inferences for an impairment charge attach to a sample taken "within a reasonable time after the alleged act" (MCA § 61-8-1002(2)). In a breath case, State v. McGowan, 2006 MT 163, the Court held that the State need not present retrograde extrapolation evidence to prove a per se offense. A long delay before a blood draw is therefore an argument about weight, built on the times in the record. See challenging the breath test.
THC and other drugs. The THC limit is 5 ng/mL "excluding inactive metabolites" (MCA § 61-8-1002(1)(d)), so the report must be read for which compound was measured. For an impairment charge based on drugs, a positive result does not by itself prove the person was under the influence, and there must be other competent evidence (MCA § 61-8-1018(1)(a)). See THC DUI and prescription and drug DUI.
The Independent Sample
In addition to any test given at an officer's direction, a person may request that an independent blood sample be drawn by a physician or registered nurse. The officer may not unreasonably impede that right but has no duty to transport the person, and the cost falls on the person requesting it (MCA § 61-8-1019(2)). If you obtained one, its result is evidence. If you asked and were prevented, tell your lawyer exactly what was said, because whether the officer unreasonably impeded the request is a factual question.
Honest Limits
A properly drawn, sealed, documented, and analyzed blood sample is strong evidence, and many are exactly that. Failure or inability to get an independent test does not keep the State's result out (MCA § 61-8-1019(2)). The cases where a blood challenge changes the outcome are the ones where the file shows a specific departure: the wrong person drew it, a seal or signature is missing, the transfers are not accounted for, or the report measures something other than what the charge requires. Getting the file is the first step, and our page on what a DUI lawyer does explains how.
This page explains Montana law in general as of the 2025 Montana Code Annotated, the Administrative Rules of Montana in effect on October 9, 2026, and the decisions cited. Every case turns on its own facts, and past results do not predict future outcomes. It is not legal advice about your specific case.