AACC AACC Specimen Collection & Processing 2 — Questions and Answers
Question 1: What is the primary reason for inverting blood collection tubes gently after venipuncture?
- To activate clotting factors in serum tubes
- To mix the additive thoroughly with the blood sample (Correct answer)
- To prevent air bubble formation in the tube
- To settle red cells to the bottom before centrifugation
Correct answer: To mix the additive thoroughly with the blood sample
Gentle inversion mixes the blood with the tube additive (anticoagulant, clot activator, or preservative) to ensure uniform distribution and proper sample preparation.
Question 2: Which specimen type is required for coagulation testing (PT/INR, aPTT), and what is the critical blood-to-anticoagulant ratio?
- Serum in a red-top tube; no specific ratio required
- Plasma from a light blue (sodium citrate) tube; 9:1 blood-to-anticoagulant ratio (Correct answer)
- Whole blood in an EDTA tube; 5:1 ratio
- Plasma from a green (heparin) tube; 4:1 ratio
Correct answer: Plasma from a light blue (sodium citrate) tube; 9:1 blood-to-anticoagulant ratio
Coagulation tests require citrated plasma (light blue tube) with a strict 9:1 blood-to-citrate ratio to ensure accurate calcium chelation and clotting factor activity.
Question 3: What is the recommended storage condition for most routine chemistry specimens (serum/plasma) if testing is delayed beyond 8 hours?
- Room temperature in the original tube
- Refrigeration at 2–8°C after separating from cells (Correct answer)
- Frozen at –20°C immediately after collection
- Stored at 37°C to prevent protein denaturation
Correct answer: Refrigeration at 2–8°C after separating from cells
Serum or plasma should be separated from cells and refrigerated at 2–8°C to slow metabolic activity and enzymatic degradation while maintaining analyte stability.
Question 4: What does the term 'hemolysis index' refer to in automated chemistry analyzers?
- A calculation of the hemoglobin A1c percentage
- A spectrophotometric measurement of free hemoglobin used to flag and quantify hemolysis (Correct answer)
- A ratio of red cell volume to plasma volume
- A QC parameter for flagging analyzer errors
Correct answer: A spectrophotometric measurement of free hemoglobin used to flag and quantify hemolysis
The hemolysis index is measured by the analyzer at 414 nm (oxyhemoglobin absorbance) to detect and quantify free hemoglobin released by lysed red blood cells.
Question 5: For ammonia testing, which pre-analytical handling requirement is most critical?
- Warming the specimen to 37°C before transport
- Immediate chilling on ice and rapid transport to the laboratory (Correct answer)
- Collecting in a sodium fluoride tube to inhibit metabolism
- Exposing the sample to room air to stabilize pH
Correct answer: Immediate chilling on ice and rapid transport to the laboratory
Ammonia is rapidly generated from amino acids and deamination at room temperature, so specimens must be chilled immediately on ice and analyzed within 15–30 minutes.
Question 6: Which specimen is the gold standard for measuring true ionized calcium in critically ill patients?
- Serum collected in a red-top tube and spun at room temperature
- Whole blood collected anaerobically in a heparinized syringe analyzed immediately (Correct answer)
- Plasma from an EDTA tube after refrigeration
- Urine from a 24-hour collection with HCl preservative
Correct answer: Whole blood collected anaerobically in a heparinized syringe analyzed immediately
Ionized calcium must be measured in whole blood collected without air exposure (anaerobically), as CO2 escape raises pH and shifts calcium to the protein-bound form, lowering ionized values.
AACC AACC Specimen Collection & Processing 2
What is the primary reason for inverting blood collection tubes gently after venipuncture?