Phlebotomy Test Point of Care Testing 1 — Questions and Answers
Question 1: Which regulatory category covers most point-of-care testing devices such as glucose meters and urine dipsticks?
- High-complexity testing
- Moderate-complexity testing
- Waived testing (Correct answer)
- Provider-performed microscopy
Correct answer: Waived testing
Most POCT devices are classified as waived tests under CLIA because they are simple to perform and pose minimal risk of harm if performed incorrectly.
Under the Clinical Laboratory Improvement Amendments (CLIA), laboratory tests are categorized by complexity. Waived tests are the simplest category and include FDA-approved home-use tests and simple lab examinations. Most POCT devices—glucose meters, urine dipstick analyzers, rapid strep tests, INR meters, and HbA1c analyzers—fall into this waived category because they have simple, clear procedures and minimal risk of harm if performed incorrectly. Waived testing still requires following manufacturer instructions, maintaining quality controls, and proper training.
Question 2: When performing quality control on a glucose meter, the QC result falls outside the acceptable range. What is the FIRST action the phlebotomist should take?
- Report the QC failure to the medical director immediately
- Repeat the QC test using fresh control solution (Correct answer)
- Continue patient testing and document the failure
- Discard the meter and requisition a new one
Correct answer: Repeat the QC test using fresh control solution
The first step when QC fails is to repeat the test with fresh control solution to rule out an error with the original control sample.
When a QC result falls outside the acceptable range on a glucose meter or other POCT device, the standard protocol is to repeat the QC test using a fresh control solution before taking further action. This is because the control solution itself may have been compromised (expired, improperly stored, or contaminated). If the repeat QC also fails, then additional troubleshooting steps are taken: check strip/reagent expiration, check the meter for errors, contact the supervisor, and take the device out of service until the issue is resolved. Patient testing must not continue on a device with unresolved QC failures.
Question 3: A patient's HbA1c POCT result is 8.2%. What does this value primarily reflect?
- Average blood glucose over the past 2–3 weeks
- Average blood glucose over the past 2–3 months (Correct answer)
- Fasting blood glucose level at the time of testing
- Postprandial blood glucose peak
Correct answer: Average blood glucose over the past 2–3 months
HbA1c reflects average blood glucose levels over the preceding 2–3 months, correlating with the lifespan of red blood cells.
Hemoglobin A1c (HbA1c) measures the percentage of hemoglobin that has glucose irreversibly attached to it. Because red blood cells have an average lifespan of 90–120 days (approximately 2–3 months), HbA1c reflects the average blood glucose concentration over that period. This makes it an excellent long-term monitoring tool for diabetes management, unlike a fasting glucose which only reflects glucose at one moment in time. A result of 8.2% indicates poor long-term glucose control, as normal is below 5.7% and the target for most diabetic patients is below 7%.
Question 4: Which anticoagulant is used in the collection tube for a POCT INR test performed on a fingerstick sample?
- EDTA
- Sodium citrate (Correct answer)
- Heparin
- Sodium fluoride/potassium oxalate
Correct answer: Sodium citrate
INR (prothrombin time) testing requires sodium citrate as the anticoagulant, which preserves coagulation factors.
Sodium citrate is the anticoagulant of choice for all coagulation studies, including prothrombin time (PT) and its derived value INR (International Normalized Ratio). Sodium citrate chelates calcium ions, which halts the coagulation cascade and preserves the coagulation factors in their natural state for accurate testing. In POCT settings, capillary blood for INR testing is collected into small sodium citrate micro-collection tubes or directly into the POCT device cartridge designed for citrated samples. This is critical for patients on warfarin therapy who require routine INR monitoring.
Question 5: A urine dipstick test shows a positive nitrite result. This finding is MOST indicative of:
- Kidney stones
- Bacterial infection (Correct answer)
- Diabetes mellitus
- Dehydration
Correct answer: Bacterial infection
Nitrites on a urine dipstick indicate the presence of nitrite-producing bacteria, which convert urinary nitrates to nitrites, suggesting a urinary tract infection.
The nitrite pad on a urine dipstick detects the presence of gram-negative bacteria (such as E. coli, Klebsiella, and Proteus) that possess the enzyme nitrate reductase. These bacteria convert dietary nitrates (found normally in urine) into nitrites. A positive nitrite result is a strong indicator of a urinary tract infection (UTI). The test must be performed on a first-morning specimen or one that has been in the bladder for at least 4 hours to allow sufficient time for bacterial conversion. False negatives can occur with dilute urine, high ascorbic acid levels, or infections with non-nitrate-reducing bacteria.
Question 6: For a rapid strep test performed at the point of care, a negative result in a symptomatic patient should typically be followed by:
- Immediate antibiotic prescription
- Throat culture to confirm the negative result (Correct answer)
- Repeating the rapid strep test on a second swab
- No further testing—a negative result rules out strep
Correct answer: Throat culture to confirm the negative result
Rapid strep tests have lower sensitivity than cultures; a negative result in a symptomatic patient should be confirmed by throat culture.
Rapid strep antigen tests detect Group A Streptococcus (GAS) antigens directly from a throat swab and provide results in 5–10 minutes. However, their sensitivity ranges from 70–90%, meaning they can produce false negatives. Throat culture has near 100% sensitivity and remains the gold standard. Clinical guidelines (from AAP and IDSA) recommend that a negative rapid strep result in a child or symptomatic patient be confirmed with a backup throat culture, particularly in high-risk populations. A positive rapid strep test does not require culture confirmation and can guide immediate antibiotic treatment.
Question 7: Which of the following is a pre-analytical error that can affect POCT glucose results?
- Incorrect calibration code on the meter
- Collecting the sample in a green-top tube
- Exposing the test strip to extreme heat or humidity
- All of the above (Correct answer)
Correct answer: All of the above
All of these are pre-analytical or analytical errors that can cause inaccurate glucose meter results, including wrong calibration codes, wrong tubes, and strip degradation.
Pre-analytical errors in POCT glucose testing can occur at multiple stages. Using an incorrect calibration code means the meter's algorithm uses wrong reference values, producing inaccurate results. Collecting blood in a green-top (heparin) tube instead of the appropriate collection method can affect glucose binding and readings. Test strips degraded by heat, humidity, or light have impaired chemical reactions that lead to falsely low or high results. Additionally, insufficient blood volume, expired strips, dirty meter ports, and failure to perform QC are all sources of pre-analytical and analytical error in POCT. Recognizing all potential error sources is essential for accurate results.
Question 8: A phlebotomist is performing a POCT glucose test. The meter displays 'HI'. What does this indicate?
- The meter needs to be calibrated
- The blood glucose is above the meter's measurable range (Correct answer)
- The QC is out of range
- The sample volume was too low
Correct answer: The blood glucose is above the meter's measurable range
'HI' on a glucose meter indicates the glucose level exceeds the upper limit of the meter's measurement range, typically >600 mg/dL.
When a glucose meter displays 'HI' (or '>600' or similar), it means the patient's blood glucose concentration exceeds the upper detection limit of the meter, which is typically around 600 mg/dL for most devices. This is a critical finding because such extremely elevated glucose levels indicate severe hyperglycemia, possibly diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS). The result should be reported immediately to the nursing staff or provider as a critical value, and a laboratory glucose test using a venous sample should be ordered for confirmation. The phlebotomist should never assume 'HI' is a device malfunction without investigating the patient's clinical status.
Phlebotomy Test Point of Care Testing 1
Which regulatory category covers most point-of-care testing devices such as glucose meters and urine dipsticks?