Blood Collection for Alcohol Intoxication Testing
For ethanol determination in suspected alcohol intoxication, collect blood in gray-top evacuated tubes containing sodium fluoride (NaF) as a preservative and an anticoagulant (typically potassium oxalate or potassium EDTA). 1, 2
Tube Selection and Specifications
Gray-top Vacutainer tubes with sodium fluoride are the standard collection tubes for forensic and clinical ethanol testing. 2, 3
Standard gray-top tubes contain 100 mg sodium fluoride and 20 mg potassium oxalate in 10-mL tubes, or proportional amounts in 6-mL tubes (providing approximately 0.25% nominal NaF concentration). 2, 4
Sodium fluoride serves as both an antimicrobial agent to prevent bacterial fermentation and an enzyme inhibitor to prevent glycolysis, thereby preserving ethanol concentration. 2, 3
Critical Collection Technique
Clean the venipuncture site with 2-propanol (isopropyl alcohol) and allow it to completely evaporate before blood draw to prevent contamination and hemolysis. 1
The median cubital vein is the preferred collection site. 1
Use a 21-gauge needle to minimize hemolysis risk. 1
Patient position (standing, lying, sitting) can affect hematocrit and analyte concentrations, so document positioning. 1
Tube Order and Handling
Follow standard order of draw protocols when collecting multiple tubes to prevent cross-contamination of additives. 1
Ensure tubes are properly filled to maintain correct blood-to-preservative ratio. 2
Label tubes immediately with patient identification and collection time. 1
Storage and Stability
Refrigerate blood samples at approximately 4°C immediately after collection. 2, 5
Ethanol remains stable in properly preserved gray-top tubes for extended periods—studies demonstrate minimal change (average decrease of only 0.004 g/100 mL) even after refrigerated storage up to 3.93 years. 2
Unopened tubes maintain ethanol stability better than opened tubes. 2
Even unpreserved blood (containing only anticoagulant) shows acceptable stability with mean ethanol decrease of only 0.012 g/dL after one year of refrigerated storage, though preserved tubes are still preferred. 5
Common Pitfalls to Avoid
Never use ethanol-containing antiseptics (such as alcohol prep pads) for skin preparation before blood draw for ethanol testing, as this can falsely elevate results. 1
Do not use expired tubes—although one study showed no statistical difference in ethanol concentrations between expired and unexpired tubes, using current tubes eliminates any potential legal challenges. 4
Avoid storing tubes unstoppered, as this theoretically allows environmental contamination, though research shows ethanol does not increase even with unstoppered storage. 3
Do not assume fermentation will occur in blood tubes—decades of research consistently show that ethanol-negative blood remains ethanol-negative with storage, and any significant change is a decrease, not an increase. 3, 5
Sodium fluoride does not cause a "salting out" effect that artificially elevates ethanol measurements; in fact, higher NaF concentrations slightly depress measured alcohol levels. 6
Alternative Testing for Recent Alcohol Use
If direct ethanol measurement is not possible or the detection window has passed (ethanol has a very short detection window), consider urinary ethyl glucuronide (EtG), which detects alcohol consumption up to 80 hours after intake with 89% sensitivity and 99% specificity. 7, 8
Hair EtG testing can detect alcohol consumption over the previous 6 months for long-term monitoring. 7