Question 1

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

Accepted Answer

It is critical that centrifugation of tubes containing serum/plasma separators be performed in swinging-bucket rotors.Use of fixed-angle rotors often leads to incomplete separation of serum/plasma from the cells, limiting the usefulness of the separator.

Question 2

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

Accepted Answer

Posture of a patient can have a significant impact on laboratory tests and result in significant preanalytical variation.Differences in hydrostatic pressure between standing, sitting, and lying in bed cause movement of water and electrolytes between intravascular and extravascular spaces.Prolonged standing can result in hemoconcentration because of hydrostatic pressure forcing fluids and electrolytes into extravascular spaces.This may result in falsely elevated results for some analytes.Lying in bed can reverse these effects and dilute analytes.The unsuspecting physician seeing changes due to variations in posture may assume these changes are related to disease.To attempt to control this source of variation, it is best to have the ambulatory patient be seated for 15 minutes prior to collecting blood samples.

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.

Accepted Answer

Platelets release potassium into serum during clot formation, causing serum potassium levels to be approximately 0.2 to 0.3 mmol/L higher than plasma levels.EDTA functions by chelating cations such as calcium, causing calcium levels to be decreased in EDTA plasma.In the evaluation of cardiac markers, it has been observed that the indicator antibody of immunoassays may be trapped during clot formation in serum.This possibility can be eliminated by the use of heparinized plasma for cardiac-marker measurements.

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.

Accepted Answer

Circadian variation refers to reproducible biological variation that occurs during the course of a single day, and infradian variation refers to reproducible biological variation that occurs over a period of greater than one day, such as in the menstrual cycle.Circannual variation is associated with seasonal variations in diet and climate, seen with Vitamin D concentrations, for example.

Question 5

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

Accepted Answer

A delta check is a comparison of analyte concentration in one specimen with that from a previous specimen to help identify laboratory errors.Analytes particularly appropriate for monitoring with delta checks are those that normally change little from one day to the next.Delta checks are not suitable for substances such as glucose that are known to vary significantly within an individual.

Question 6

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

Accepted Answer

To avoid contamination between collection tubes, tubes for coagulation testing should be collected first to ensure that there is no interference with coagulation testing from subsequent tubes.This is followed by tubes that have no anticoagulant, then heparin-containing tubes, and finally EDTA-containing tubes.EDTA-containing tubes are at the end of the collection order because of the many possible interferences that EDTA can have on laboratory assays, as well as the analyte itself.

Question 7

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

Accepted Answer

The most common cause of inaccurate specimen identification is the phlebotomist's failure to label specimens before leaving the patient's bedside.

Question 8

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

Accepted Answer

With prolonged sitting, the sodium/potassium pump that keeps potassium in the red blood cell runs out of energy.Potassium that leaks out of red cells will begin to accumulate in the small amount of fluid beneath the separator gel.If the tube is re-centrifuged, this small amount of fluid will migrate to the other side of the gel and will be highly concentrated with potassium.If this fluid is used for potassium analysis, a falsely elevated result will be obtained.

Question 9

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

Accepted Answer

Postprandial refers to something occurring following a meal-in this case, changes in analyte concentration.Substances derived from a meal (e.g., triglycerides and glucose) are anticipated to increase.Likewise, hormones that are secreted in response to eating (e.g., gastrin) will also show a postprandial increase.The only analyte listed that does not show a postprandial increase is potassium.Plasma potassium levels decline postprandially due to the action of insulin, which will move potassium into the red blood cell.

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?

Accepted Answer

Diurnal variations appear to be influenced by sleeping and waking rather than the actual time of the day.Since the sleep/wake pattern of the patient appears to be in question, it would be difficult to identify an appropriate time for specimen collection.Combining this with the desire for an overall picture of analyte production, analysis of the analyte in a 24-hour urine should be the recommendation.

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?

Accepted Answer

Arterial blood is the source for nutrients, such as glucose, for the body.Arterial glucose levels are normally higher than venous glucose levels.This notation on the patient's laboratory report notifies the physician that they should not base a decision on the published normal reference ranges on the laboratory report.

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?

Accepted Answer

Tris-(2-butoxyethyl) phosphate (TBEP) is found in older formulations of evacuated tube stoppers as a plasticizer.This plasticizer displaces many drugs from their transport protein.Once drugs become free in the blood stream, they diffuse into red blood cells, causing the total concentration of drug in the blood stream (free drug plus that bound to protein) to decrease.

Question 13

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

Accepted Answer

Potassium, magnesium, and lactate dehydrogenase are highly concentrated in the red blood cell.For example, lactate dehydrogenase is 150 times higher, and potassium is 30 times higher in concentration within the red blood cell than in serum.During hemolysis, these materials are released into the blood stream, causing their concentration to increase while diluting other materials (e.g., sodium) in the blood stream.

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?

Accepted Answer

The sample must be recollected.It is important to ensure that the proportion of blood and anticoagulant is constant for all assays performed.In specimens with inadequate blood volumes, there may be a significant dilution of the blood by the anticoagulant solution.

Question 15

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

Accepted Answer

Contamination of the blood sample with tissue fluid is a potential concern in all capillary blood collection procedures.Tissue fluid contains virtually no protein and therefore no protein-bound analytes.Thus dilution of the blood sample with tissue fluid will dilute all of these analytes.Tissue fluid contamination may be minimized by collecting only free flowing blood from the puncture site."Milking" by applying pressure near the puncture site is a common source of preanalytical variation and error.

Question 16

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

Accepted Answer

Creatinine production occurs on a relatively constant basis and is removed from the body almost exclusively by urinary excretion.As a result, creatinine serves as a reliable measure of the completeness of a 24-hour urine collection; 24-hour urine specimens with too much or too little creatinine usually indicate an improperly timed collection.

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?

Accepted Answer

Of the analytes listed, TSH is the only analyte found in higher concentration in the afternoon and evening than in the morning

Quiz 18: Sources and Control of Preanalytical Variation