Phlebotomy Test Point of Care Testing 2 — Questions and Answers
Question 1: Which POCT test is used to monitor patients on heparin therapy in an acute care setting?
- INR
- Activated clotting time (ACT) (Correct answer)
- D-dimer
- Fibrinogen level
Correct answer: Activated clotting time (ACT)
Activated clotting time (ACT) is a bedside POCT used to monitor unfractionated heparin therapy, especially in cardiac catheterization labs and surgical suites.
Activated clotting time (ACT) is a point-of-care test commonly used in settings where rapid assessment of heparin anticoagulation is needed, such as cardiac catheterization laboratories, cardiac surgery, and interventional radiology. The test measures the time for whole blood to clot after activation with a contact activator. It is preferred over aPTT in these settings because it can be performed bedside with results in minutes on whole blood samples. INR monitors warfarin therapy, not heparin. D-dimer and fibrinogen are diagnostic markers for thrombosis or coagulopathy, not real-time heparin monitoring tools.
Question 2: When using a glucose meter for POCT, the operator must enter a lot number or scan a barcode before testing. This step primarily ensures:
- Patient identification is recorded
- The correct calibration data matches the test strips in use (Correct answer)
- The QC has been performed within 24 hours
- The meter's battery level is adequate
Correct answer: The correct calibration data matches the test strips in use
Entering the lot number or scanning the test strip code loads the correct calibration data specific to that batch of strips, ensuring accurate results.
Most glucose meters require the operator to enter a calibration code, scan a barcode, or use a calibration chip/strip specific to the lot of test strips being used. This is because each manufacturing lot of test strips has slight variations in the chemistry of the reagent layer. The calibration code adjusts the meter's algorithm to account for these lot-specific variations, ensuring accurate glucose measurements. Using the wrong code or failing to update it when opening a new box of strips can lead to systematic errors—results that are consistently too high or too low across all patient tests, a serious patient safety issue.
Question 3: A POCT urine dipstick result shows leukocyte esterase 2+ and nitrite positive. These findings together are MOST consistent with:
- Nephrotic syndrome
- Urinary tract infection (Correct answer)
- Glomerulonephritis
- Renal tubular acidosis
Correct answer: Urinary tract infection
The combination of positive leukocyte esterase (WBCs in urine) and positive nitrite (bacteria converting nitrates) is the classic dipstick pattern for a UTI.
Leukocyte esterase is an enzyme released by white blood cells (neutrophils) in the urine; its presence indicates pyuria (WBCs in urine), which accompanies infection or inflammation. Nitrite positivity indicates the presence of gram-negative bacteria with nitrate reductase activity. The combination of both findings is highly suggestive of a bacterial urinary tract infection (UTI), with sensitivity around 75% and specificity around 82% when both are positive. Nephrotic syndrome presents with heavy proteinuria and no infection markers. Glomerulonephritis shows hematuria and proteinuria. Renal tubular acidosis is characterized by abnormal pH but no infection markers.
Question 4: What is the purpose of running both high and low controls on a POCT device?
- To calibrate the device before each patient test
- To verify the device performs accurately across the reportable range (Correct answer)
- To determine if patient samples need dilution
- To check the battery and display function
Correct answer: To verify the device performs accurately across the reportable range
Running high and low controls verifies that the device produces accurate results at both extremes of the reportable range, catching errors that affect only one end of the scale.
Quality control for POCT devices typically involves running at least two levels of control solution: a low control (with an analyte concentration near the lower end of the normal or reportable range) and a high control (near the upper end). Running both levels verifies that the device's accuracy is maintained throughout its entire reportable range, not just at one concentration. A device might perform well at normal levels but produce errors at critically high or low values. Two-level QC catches systematic bias, imprecision, and reagent deterioration that might otherwise go undetected. Results must fall within the manufacturer-defined acceptable range (mean ± 2 SD) for the controls to pass.
Question 5: Which specimen type is required for a fingerstick HbA1c test at the point of care?
- Serum from a red-top tube
- Capillary whole blood (Correct answer)
- Plasma from a lavender-top tube
- Urine sample
Correct answer: Capillary whole blood
POCT HbA1c analyzers use capillary whole blood obtained via fingerstick, which contains the red blood cells needed to measure glycated hemoglobin.
HbA1c is a measure of glycated hemoglobin within red blood cells. POCT HbA1c analyzers (such as the Afinion or A1cNow devices) are specifically designed to use capillary whole blood obtained by fingerstick. The whole blood sample is necessary because the test measures the percentage of hemoglobin A that has glucose attached to it—a process that occurs within the red blood cell. Serum and plasma do not contain intact red blood cells and therefore cannot be used. The capillary sample is typically collected into a specialized capillary tube or directly applied to the test cartridge as specified by the manufacturer.
Question 6: A phlebotomist notices that the POCT glucose test strips expired yesterday. The correct action is to:
- Use them for one more day since they are only slightly expired
- Discard them and use a new, in-date lot of strips (Correct answer)
- Perform extra QC runs to verify the strips still work
- Notify the supervisor but continue using them for patient testing
Correct answer: Discard them and use a new, in-date lot of strips
Expired test strips must be discarded and replaced; using them can produce inaccurate results, posing a patient safety risk regardless of how recently they expired.
Test strip reagents undergo chemical degradation over time. Once a test strip has passed its expiration date, the manufacturer can no longer guarantee the accuracy of results produced with that strip. Using expired strips is a violation of CLIA regulations and can result in inaccurate glucose readings—either falsely low or falsely high—leading to inappropriate clinical decisions that harm patients. The correct action is to immediately remove and discard the expired strips, replace them with a new, in-date lot, update the calibration code if the lot number changed, and run QC before resuming patient testing. This must be documented in the QC log.
Question 7: In a POCT setting, delta check refers to:
- The difference between high and low QC values
- Comparison of a patient's current result with their previous result (Correct answer)
- The allowable error range for a QC result
- Calibration verification performed quarterly
Correct answer: Comparison of a patient's current result with their previous result
A delta check compares a patient's current test result with their most recent previous result to detect implausible changes that may indicate sample or patient identification errors.
A delta check is a quality assurance tool in which the laboratory's information system automatically compares a patient's current laboratory result with their most recent previous result for the same analyte. If the difference exceeds a predefined threshold (the 'delta limit'), an alert is triggered for review before the result is reported. In POCT, delta checks are used to detect mislabeled specimens, wrong patient samples, transcription errors, and true rapid clinical changes. For example, a sodium level changing by more than 10 mEq/L in 24 hours would trigger a delta check alert. Delta checks are a critical component of pre-analytical and post-analytical quality control.
Question 8: Which of the following factors can cause a falsely LOW glucose reading on a POCT glucose meter?
- High altitude
- Elevated hematocrit (polycythemia) (Correct answer)
- Elevated uric acid levels
- Dehydration
Correct answer: Elevated hematocrit (polycythemia)
An elevated hematocrit (polycythemia) causes falsely low glucose readings on many glucose meters because more blood volume is occupied by red blood cells, diluting the plasma glucose signal.
Most glucose meters are calibrated using whole blood but report plasma-equivalent glucose concentrations. The hematocrit of the sample significantly affects accuracy. In patients with elevated hematocrit (polycythemia vera, neonates, COPD patients), the proportion of red blood cells is higher, which reduces the available plasma volume. Since glucose resides primarily in plasma, a higher hematocrit means less plasma and effectively less glucose in the capillary sample volume tested, leading to falsely low readings. Conversely, anemia (low hematocrit) can cause falsely elevated readings. Manufacturers specify acceptable hematocrit ranges in their package inserts (typically 20–60%), and results outside this range should be confirmed with a laboratory method.
Phlebotomy Test Point of Care Testing 2
Which POCT test is used to monitor patients on heparin therapy in an acute care setting?