Skip to main content

Hematology

Point-of-Care Testing

Point-of-Care Testing (POCT), often referred to as bedside testing or near-patient testing, is laboratory analysis performed outside of the central laboratory, close to the site of patient care. In Hematology, POCT is widely utilized for rapid turnaround times in critical care settings, anticoagulation clinics, and operating rooms. While POCT offers speed and convenience, it presents unique challenges in Quality Assessment (QA) because the testing is frequently performed by non-laboratory personnel (nurses, respiratory therapists, perfusionists) rather than trained laboratory scientists. Consequently, the oversight, training, and troubleshooting provided by the laboratory department are critical to patient safety

Common POCT Methodologies

To troubleshoot POCT effectively, one must understand the specific methodologies used, as they often differ from the principles used in central laboratory automation (such as impedance or flow cytometry)

  • Hemoglobin (Photometric): Devices like the HemoCue utilize microcuvettes containing reagents (sodium azide or sodium lauryl sulfate) that lyse RBCs and convert hemoglobin to a stable colored compound (e.g., azidemethemoglobin). The device measures absorbance. Air bubbles in the cuvette or fingerprints on the optical window are common sources of error
  • Hematocrit (Conductivity): Handheld blood gas analyzers (e.g., i-STAT) often measure Hematocrit via conductivity (electrical resistance). The plasma conducts electricity; RBCs act as insulators. The device measures conductivity to determine packed cell volume and calculates the Hemoglobin
    • Interference: Because this method assumes normal plasma protein levels, patients with hypoproteinemia or hyperproteinemia may have falsely low or high hematocrit results, respectively
  • Coagulation (INR/ACT): These devices use electrochemical or mechanical detection of clot formation. They use specific cartridges containing thromboplastin (for PT/INR) or an activator like kaolin/celite (for Activated Clotting Time - ACT). These enzymatic reactions are highly temperature-sensitive

Quality Assessment in POCT

The Quality Assessment framework for POCT is rigorous due to the high volume of operators and the portable nature of the equipment. The laboratory scientist often serves as the POCT Coordinator, overseeing compliance and troubleshooting

Preanalytical QA (The Operator & Specimen)

The majority of POCT errors occur in the preanalytical phase, largely due to technique variations among non-laboratory staff

  • Patient Identification: POCT devices usually require scanning a patient wristband. Bypassing this step or scanning a chart label instead of the patient’s wristband is a major source of error
  • Capillary Puncture Technique: Many Hematology POCT tests use fingersticks
    • Interstitial Fluid Contamination: “Milking” or forcefully squeezing the finger introduces tissue fluid, which dilutes the sample (causing false low Hgb/Hct) and introduces Tissue Factor (activating the extrinsic pathway, causing false short clotting times)
    • Alcohol Residue: Failure to let alcohol dry causes hemolysis and interferes with enzyme-based coagulation sensors
  • Cuvette/Cartridge Integrity: Reagents for POCT often come in vials or individual pouches
    • Humidity: Leaving a vial of hemoglobin microcuvettes open exposes them to humidity, inactivating the reagent
    • Storage: Refrigerated cartridges must be brought to room temperature before use to prevent temperature errors during the reaction

Analytical QA (QC & Lockouts)

POCT devices utilize specialized QC protocols to ensure results are not generated on faulty instruments

  • Electronic Quality Control (EQC): Many handheld devices use an internal electronic check (a “simulator”) that verifies the internal circuitry, optics, and thermal control every time the device is powered on or a cartridge is inserted. While efficient, EQC does not check the integrity of the liquid reagent or the operator’s technique
  • Liquid Quality Control (LQC): Traditional external control material must be run at defined intervals
    • Frequency: Generally required with each new lot of reagents, each new shipment, whenever the batteries are changed, or if the device is dropped
    • QC Lockout: This is a critical QA feature. If Liquid QC is not run or fails, the instrument software “locks out” the user, preventing patient testing until the issue is resolved. This prevents the use of a drifting instrument on a patient
  • Operator Lockout: Devices are programmed to accept only valid Operator IDs. If an operator’s competency has expired (usually annually), the device will not allow them to perform tests

Postanalytical QA (Data Management)

  • Connectivity: Modern POCT focuses on interfacing devices directly to the LIS (Laboratory Information System) via docking stations or Wi-Fi. This eliminates transcription errors, which are common when results are manually written in charts
  • Critical Values: POCT operators must be trained to recognize critical limits (e.g., INR > 5.0 or Hgb < 7.0 g/dL)
  • Confirmatory Testing: A vital policy in Hematology POCT is the “Confirmatory Rule.” If a POCT result is critical, questionable, or does not match the clinical picture, a venous sample must be drawn and sent to the central laboratory for analysis on the main analyzer. The central lab result is considered the gold standard

Regulatory Compliance (CLIA)

Most Hematology POCT falls under CLIA (Clinical Laboratory Improvement Amendments) regulations. The complexity of the test dictates the level of oversight

  • Waived Testing: Tests cleared by the FDA for home use (simple, low risk of erroneous results). However, laboratories must still follow the manufacturer’s instructions for QC. Failure to follow the manufacturer’s inserts turns a Waived test into a High Complexity test in the eyes of inspectors
  • Competency Assessment: The POCT Coordinator must assess every operator (nurses, etc.) upon hire, at 6 months, and annually thereafter. This assessment must include:
    • Direct observation of testing
    • Monitoring of QC performance
    • Test of problem-solving skills (troubleshooting)
  • Correlations: For non-waived testing, the laboratory must perform a method comparison study every 6 months, comparing the POCT device results against the central laboratory analyzer to ensure accuracy

Troubleshooting Common POCT Problems

When a POCT device fails or produces erratic results, the laboratory scientist must guide the remote operator through troubleshooting

  • “R Codes” or Flow Errors: In microfluidic devices (like i-STAT), this usually indicates the sample clotted before insertion, the cartridge was overfilled/underfilled, or air bubbles were trapped over the sensor
  • QC Failure (High/Low)
    • Check Consumables: Was the QC vial left out of the fridge too long? Has the open-vial stability expired?
    • Check Technique: Was the QC bottle inverted/mixed properly? (Unmixed Hgb controls settle quickly)
  • Temperature Errors: Coagulation POCT is strictly temperature controlled (37°C). If a device was left in a cold car (home health setting) or near an A/C vent, it may fail to initialize or produce prolonged clotting times. The device must be moved to a stable environment
  • Battery/Power: Low battery voltage can disrupt the heating elements in handheld analyzers, leading to error codes. Regular docking ensures proper charge and data synchronization