Cross-Examining a GBI Toxicologist in a Gwinnett County DUI Blood Case
George C. Creal, Jr., P.C. — Trial Lawyers
Gwinnett County and Metro Atlanta DUI Defense www.georgecreal.com | (404) 333-0706
A Gwinnett DUI jury often hears one number: the blood-alcohol result from the Georgia Bureau of Investigation, Division of Forensic Sciences. The State treats that number as the end of the case. It is not.
The toxicologist did not watch the draw, did not ride in the patrol car with the kit, and did not see the defendant drive. The witness measured ethanol in a tube. Under O.C.G.A. § 40-6-392, that measurement is admissible only if the test was performed by approved methods, on a working instrument, by a person with a valid DOFS permit. Cross-examination is how the defense tests whether those conditions were met.
This article is general education, not legal advice and not a script for any particular case.
Why Gwinnett blood cases look the way they do
Gwinnett DUI blood draws commonly happen at a hospital or jail after an arrest by Gwinnett County Police, Gwinnett Sheriff’s deputies, or a city department inside the county. Gwinnett Police Officers and Georgia State Patrol Troopers commonly draw the blood in an unsanitary county jail intake area and not in a sanitized hospital environment by a hospital employed phlebotomist who does this everyday. The gray-top kit is supposed to go to Georgia Bureau of Investigation Division of Forensic Services (GBI-DOFS). The official report then comes back to the Gwinnett County Solicitor-General (misdemeanor State Court) or the District Attorney (felony or serious-injury cases).
The chemist who signs the report is usually the State’s last clean-looking witness. Jurors assume a state crime lab cannot be wrong. The job of cross is to slow that assumption down and walk through three windows where error actually lives:
Before the lab — identity, draw, kit, storage
Inside the lab — method, chromatograms, controls, uncertainty
After the lab — the report versus the leftover tube
That structure follows the same forensic logic used in blood-alcohol error checklists: chain of custody, collection, storage, qualitative analysis, quantitative analysis, and re-testing.
What the toxicologist can and cannot say
A proper first block of questions is about the limits of the witness.
The toxicologist did not identify the defendant at the hospital. The toxicologist cannot describe driving, speech, or field sobriety tests. The toxicologist is not a medical doctor offering an impairment diagnosis from a chromatogram. Under professional forensic-toxicology testimony standards, the witness may explain the method, the result, and the limitations. The witness should not smuggle a “less safe” opinion into a lab number.
Confrontation matters here. If the State tries to put the report in through a supervisor who never tested the sample, that is the problem addressed in Bullcoming v. New Mexico, 564 U.S. 647 (2011), and Smith v. Arizona, 602 U.S. 779 (2024). The defense is entitled to question the analyst who actually did the work.
Window one: whose blood, and how was it drawn?
GBI can only analyze what arrives. If the label is wrong, the number belongs to the wrong person.
Cross should force a line-by-line match of name, date of birth, agency case number, kit number, and draw time across:
the tube label
the outer kit
the submission form
the Laboratory Information Management System (LIMS) entry
the final report
A “scrivener’s error” is not a small thing when the State is asking a Gwinnett jury to convict on a hundredth of a gram.
O.C.G.A. § 40-6-392(a)(2) limits who may draw blood for alcohol content: a physician, registered nurse, laboratory technician, Emergency Medical Technician (EMT), State Licensed Phlebotomist or other qualified person. The toxicologist almost never watched that draw. That means the State still needs the phlebotomist or a proper foundation on:
non-alcohol skin prep (alcohol swabs are a contamination issue)
whether an IV was running
venous versus arterial blood
whole blood versus serum or plasma
volume in the tube (a short draw changes the blood-to-powder ratio)
whether the gray-top actually contained the expected sodium fluoride preservative and potassium oxalate anticoagulant
lot number, expiration, and recall status
The Georgia Bureau of Investigation’s (GBI) own toxicology guidance expects traffic blood in approved collection kits. A kit that sat unrefrigerated in a Gwinnett patrol car or property room is not the same sample the chemist later treats as pristine.
Storage is its own chapter. Microbes in a warm, under-preserved tube can produce ethanol. If the lab has no temperature history from hospital to refrigerator, the witness cannot exclude fermentation. The chemist also usually did not Gram-stain or culture the tube before running it.
Window two: what the instrument actually saw
Most GBI alcohol work in traffic cases is headspace gas chromatography. While dual-column setup is the gold standard configuration used by forensic laboratories employing Gas Chromatography with Flame Ionization Detection (GC-FID) to prevent co-elution (an analytical chemistry and biochemistry process where two or more different compounds emerge from a chromatography column at the same time. [1, 2]) and confirm compound identity, the GBI circumvents the need for a second column by utilizing Mass Spectrometry (MS) as the detector. However, GBI does not use the free NIST MS library of 382,180 known compounds for alcohol sample comparison. GBI uses a home brew library of five alcohol adjacent or similar compounds. Imagine trying to identify a Chevrolet automobile model but you only had Ford automobile models to compare. You would have to choose the closest Ford model of automobile.
The MS fragmentizes the molecules and provides positive structural identification based on mass-to-charge ratios (m/z), a single analytical column allegedly provides sufficient legal and scientific defensibility when paired with headspace technology. [1, 2, 3, 4] That method is better than a hospital enzyme screen but not as good as a dual column FID GC/MS. It is definitely not magic or a foregone conclusion.
Useful questions:
Which method was used, and where does it sit on the reliability ladder from enzyme assay up to GC-MS?
What internal standard was used?
Were internal-standard area counts in this blood sample the same as in the watery calibrators? If the internal standard is suppressed in blood, the ethanol number can read high. That is a matrix-effect problem, not a jury-friendly “the machine said so” problem.
Do the chromatograms show a flat baseline, symmetrical peaks, and the expected peaks only?
Does the negative control contain ethanol? It should not.
Did both columns confirm ethanol? – Is the calibration curve linear? What are R and R²?
Were the batch controls on target? Were they expired?
What do six months of control charts and proficiency tests show on this instrument?
Then the question Georgia juries understand: uncertainty.
A forensic result is a measured value plus a range. If the report is 0.084 grams percent and the expanded uncertainty is several percent, the true value may sit under Georgia’s 0.080 per se line in O.C.G.A. § 40-6-391(a)(5). Ask whether the lab’s uncertainty budget included only clean aqueous controls, or also short draws, blood-water variation, matrix effects, and pre-lab heat. If those sources were left out, the reported plus-or-minus is too small.
whether it can be re-tested for ethanol and other volatiles
whether identity can be checked by DNA if the label is disputed
whether microbes can still be looked for if fermentation is the defense
If GBI already exhausted or destroyed the tube, the defense lost the only physical evidence that could contradict the report.
The questions that belong to other witnesses
Do not waste the chemist on facts the chemist never knew. The officer and the blood drawer own:
implied-consent warnings
the independent-test request and whether Gwinnett officers reasonably accommodated it
hospital identification
the antiseptic
the kit seal and the ride to the lab
The toxicologist owns the hour the tube was on the instrument. Keep the lanes separate. That is how a Gwinnett State Court jury follows the story.
Discovery that should be on file before the chemist takes the stand
official report and uncertainty statement
subject, blank, calibrator, and control chromatograms
batch sequence and LIMS audit trail
kit and tube lot, expiration, recall search
draw records
storage timeline
SOP, validation, calibration curve
six months of controls and proficiency tests on that instrument
analyst permit
remaining-sample log
Without those records, the State is asking the jury to trust a number the defense was not allowed to test.
What this means in a real Gwinnett DUI
A blood result over 0.080 is not an automatic conviction. It is a measurement that has to survive identity, collection, storage, chromatography, controls, and uncertainty. Some cases should be tried on those issues. Some should be negotiated once the solicitor sees the chromatogram or the broken chain. Either way, the work happens before the toxicologist walks into the Lawrenceville courthouse.
George C. Creal, Jr., P.C. defends DUI and criminal cases in Gwinnett State Court, Gwinnett Superior Court, and the municipal courts that feed those dockets.
