Deck 18: Sources and Control of Preanalytical Variation

Question 1

Which of the following is not an advantage of the use of serum/plasma separator tubes?

A)Tubes can be centrifuged without removal of the stopper.
B)Tubes can be centrifuged using swinging buckets or fixed-angle rotors.
C)Continued red cell metabolism does not alter serum or plasma.
D)Storage with stoppers in place prevents evaporation.

Answer 1

Tubes can be centrifuged using swinging buckets or fixed-angle rotors.

Question 2

Which of the following should be required of ambulatory patients to minimize the preanalytical effect of posture on laboratory test results?

A)The patient should be seated for 15 minutes prior to blood collection.
B)The patient should be allowed to stand quietly or be seated for 15 minutes prior to blood collection.
C)The patient should be allowed to stand quietly, be seated, or lie down for 15 minutes prior to blood collection.
D)There should be no restrictions on ambulatory patients.

Answer 2

The patient should be seated for 15 minutes prior to blood collection.

Question 3

An important preanalytical variable is associated with the use or non-use of anticoagulants.Which of the following statements related to use or non-use of anticoagulants are correct?
1)The measured total protein level is the same in serum and heparinized plasma.
2)Platelets release potassium during clotting.
3)The use of EDTA plasma will falsely decrease plasma calcium.
4)Heparinized plasma is preferred over serum for cardiac marker evaluation.

A)1, 2, 3, 4
B)1, 2, 3
C)2, 3, 4
D)1, 3, 4

Answer 3

2, 3, 4

Question 4

Cyclic variations refer to changes in concentration of analytes that occur in a predictable manner.______ variation is a phrase used to describe reproducible variation that occurs during the course of a single day, and ______ variation is a phrase used to describe reproducible variation that occurs over a period of greater than one day.

A)circannual, circadian
B)circadian, infradian
C)infradian, circannual
D)circadian, circannual

Question 5

Why is glucose typically not considered to be an analyte suitable for delta-check monitoring?

A)Glucose methodology does not provide sufficiently reproducible results.
B)Glucose tests are ordered too frequently.
C)Glucose shows pronounced intra-individual variation.
D)Glucose levels can be measured in serum, plasma, urine, and spinal fluid.

Question 6

For the specimen collection tubes listed below, select the proper order of use during specimen collection.

A)heparin-containing tube, tube for coagulation testing, EDTA-containing tube, tube with no anticoagulant
B)EDTA-containing tube, heparin-containing tube, tube with no anticoagulant, tube for coagulation testing
C)tube with no anticoagulant, EDTA-containing tube, tube for coagulation testing, heparin-containing tube
D)tube for coagulation testing, tube with no anticoagulant, heparin-containing tube, EDTA-containing tube

Question 7

Over 99% of specimen identification errors that occur by laboratory personnel result from:

A)improper patient identification
B)failure to label specimens before leaving the room
C)errors in data entry
D)selection of the wrong patient sample on which to perform laboratory analyses

Question 8

Which of the following may result in an elevated serum/plasma potassium level?

A)use of a needle diameter that is too small during specimen collection
B)use of a needle diameter that is too large during specimen collection
C)re-centrifugation of tubes with separator gels
D)both a and b

Question 9

A postprandial rise is expected with many analytes.Which of the following will show a postprandial decrease?

A)triglycerides
B)potassium
C)glucose
D)gastrin

Question 10

Which of the following would be recommended to a physician who is concerned about getting an overall picture of analyte production for a material that is known to exhibit circadian variation in a patient who has unpredictable sleep/wake patterns?

A)random blood level
B)8 a.m.fasting blood level
C)8 a.m.and 8 p.m.blood levels
D)24-hour urine level

Question 11

Typically, serum or plasma glucose levels are measured on venous blood samples.Suppose an arterial sample is used to measure the glucose level for a particular patient.Why should the use of an arterial sample for this patient's glucose be noted on the patient's laboratory report?

A)Procedures used to analyze glucose in venous blood and arterial blood are different.
B)The normal reference ranges for glucose differ for the two samples.
C)The medical staff needs an accurate record of all blood collections.
D)Arterial samples require more lengthy laboratory assays, and this notation explains the delay.

Question 12

Blood samples for therapeutic drug monitoring that are collected in evacuated tubes with stoppers containing tris-(2-butoxyethyl) phosphate (TBEP) as the plasticizer are subject to which of the following?

A)falsely decreased serum concentrations of monitored drugs due to the plasticizer's ability to displace drugs from transport proteins
B)falsely increased serum concentrations of monitored drugs due to the plasticizer's ability to displace drugs from transport proteins
C)falsely decreased serum concentrations of monitored drugs due to the dilutional effect of plasticizer being released into the blood sample
D)falsely increased serum concentrations of monitored drugs because the plasticizer is measured as part of the drug concentration

Question 13

Which of the following analytes is found decreased in a hemolyzed serum specimen?

A)sodium
B)potassium
C)magnesium
D)lactate dehydrogenase

Question 14

Suppose a phlebotomist returns to the laboratory with a heparin tube that is less than one-third full after patient collection.Given that the heparin anticoagulant is in liquid form, which of the following steps should be taken?

A)Order a recollect.
B)Analyze the sample as it was received, as long as there are no visible clots.
C)Dilute the sample to full volume, mix for 15 minutes, and analyze as normal, multiplying the final result of the analysis by a factor of 3.
D)Perform manual measurements for the analyte of interest.

Question 15

Which of the following is the major source of preanalytical error when collecting capillary blood samples?

A)failure to collect enough sample for the analysis
B)failure to add anticoagulant to the capillary tube prior to collection
C)failure to mix the sample collected with anticoagulant in the capillary tube
D)failure to use only free-flowing blood from the puncture site

Question 16

Which of the following is typically used as a measure of the completeness of a 24-hour urine collection?

A)creatinine
B)urea nitrogen
C)calcium
D)protein

Question 17

Given that all of the following analytes show circadian variation, which one is known to be higher in the afternoon and evening than in the morning?

A)cortisol
B)ACTH
C)TSH
D)iron