Specimen Collection and Pre-Analytical Processing Flashcards

A patient's potassium is 7.8 mmol/L and calcium is 3.1 mg/dL, with no clinical signs of either abnormality. What is the most likely pre-analytical cause?

Answer: K2EDTA carryover or contamination of the chemistry specimen

EDTA is a potassium salt that also chelates calcium, so contamination falsely raises K and lowers Ca.

Which specimen requires transport on ice slurry and analysis within 30 minutes?

Answer: Ammonia

Ammonia rises in vitro from red cell and amino acid metabolism, so it must be chilled and tested quickly.

A sodium citrate tube for PT/INR is drawn from a patient with a hematocrit of 62%. What adjustment is recommended?

Answer: Reduce the volume of citrate in the tube

High hematocrit means less plasma, so citrate must be reduced to keep the proper anticoagulant-to-plasma ratio.

Which specimen must be kept at 37°C from collection until the serum is separated?

Answer: Cryoglobulin

Cryoglobulins precipitate in the cold and would be lost in the clot if the specimen cools before separation.

When a specimen must be drawn through an indwelling heparinized line for a coagulation test, what is the recommended practice?

Answer: Flush with saline and discard about 5 mL or 6 dead-space volumes before collecting

CLSI recommends discarding about 5 mL or six times the line's dead-space volume to avoid heparin contamination.

Glucose in an unseparated serum specimen left at room temperature decreases by about how much per hour?

Answer: 5–7%

Glycolysis by blood cells consumes glucose at roughly 5–7% per hour at room temperature.

For therapeutic drug monitoring, when is a trough level typically collected?

Answer: Immediately before the next scheduled dose

The trough is the lowest serum concentration, which occurs just before the next dose.