Trace Metals and Point of Care Testing

Trace Metals

• Also known as trace elements or microminerals, essential minerals required by the body in very small amounts
• Collected in royal blue EDTA tubes
• Examples of trace metals include:
  • Aluminum
  • Mercury
  • Arsenic
  • Selenium
  • Cadmium
  • Thallium
  • Chromium
  • Zinc
  • Copper
  • Lead
  • Manganese

Point of Care Testing (POCT)

• Testing done at the patient's bedside or near patient testing, instead of in a lab
• Brings laboratory testing to the location of the patient
• Example of POCT: glucometer, used to test blood sugar
• Advantages of POCT:
  • Small amount of blood required
  • Rapid turnaround time (TAT)
  • Easy to perform (1 or 2 steps)
  • Accuracy and precision comparable to central laboratory analyzers
  • Minimum QC tracking
  • Data can be interfaced with other LIS or software
• Convenience to the patient:
  • No need to go to the lab every time
  • Prompt medical attention
  • Quicker patient recovery
  • Improves access to healthcare services in rural locations
  • Decreases patient care costs
• Disadvantages of POCT:
  • Cost per test (more expensive than central laboratory testing)
  • Degree of maintenance required
  • Sources of POCT error:
    • Pre-analytical errors
    • Operator incompetence
    • Non-adherence to test procedures
    • Use of uncontrolled reagents and equipment
• Infectious control issues:
  • Minimize the changes of fomites on POCT machines and patients by disinfecting POCT machines with 1:10 bleach
  • Glucometers perform one test, but POC machines can perform multiple tests (e.g., glucose and cholesterol levels, electrolytes, and enzyme analysis)

I-Stat

• A POC machine that can perform multiple tests
• Example of tests performed:
  • Sodium (Na)
  • Potassium (K)
  • Chloride (Cl)
  • TCO2
  • Ionized Calcium (iCa)
  • Glucose (Glu)
  • Urea Nitrogen/Urea
  • Creatinine (Crea)
  • Lactate
  • cTnI
  • CK-MB
  • β-hCG

POCT Quality Control

• Anyone who does POCT should be able to carry out quality control and maintenance procedures
• External quality control:
  • Performed as per manufacturer guidelines
  • Liquid quality control is a liquid of a known result, applied to the POCT instead of blood
  • Electronic QC's (EQC's) are built into instruments to detect certain problems
  • Internal checks to determine if the instrument is functioning properly
  • Automatic lockout of users who are not authorized or do not adhere to QC procedures
• All control results must be recorded on some type of document and reviewed for consistency and acceptability

Glucometer Testing

• Prepare the lancing device by selecting the depth of penetration
• Obtain a drop of blood by pressing the lancet device against the finger and pressing a button
• Dispose of the used lancet by pressing the eject button on the device
• Insert a test strip, and the monitor will automatically turn on
• Touch and hold the drop of blood to the edge of the sample area of the test strip
• Glucose result will be displayed within a few seconds
• Discard the used test strip in a biohazard container

Other POCT Tests

• Hemoglobin A1C
• Cholesterol Point of Care
• Urinalysis
• Pregnancy tests:
  • Use urine or serum samples
  • There are many different types of kits available
  • Must use suitable time after fertilization to allow B-HCG to rise to a significant level
  • First morning specimen is required because it contains the highest concentration of the hormone
  • Must be collected in a clean plastic container
  • Can be refrigerated up to 2 days or frozen (-20°C) for 1 year
• Multiple-Test-Panels by POCT:
  • Measure multiple tests such as electrolytes, urea, glucose, lactate, and hemoglobin
  • Usually found in ICU or ER
  • Play an important role in life-threatening situations

Hemolysis

• Breakdown of red blood cells, affecting lab results
• Effects of hemolysis on chemistry results:
  • Slight change:
    • Phosphate, total protein, albumin, magnesium, calcium, alk phos
    • Haptoglobin, bilirubin
  • Moderate change:
    • ALT, CK, iron
    • T4
  • Gross change:
    • K, LD, AST
    • Troponin, glucose