Special Collections & Point of Care Testing

Special Collections and Point of Care Testing

Introduction

  • Discussing special collections and point-of-care testing as the last topics of the term.
  • Differentiating these procedures from routine laboratory tests.

Special Collections

Routine vs. Special Phlebotomy
  • Routine phlebotomy: common tests for chemistry, hematology, etc., using evacuated tubes.
  • Special phlebotomy: procedures not routinely performed in the lab.
Blood Donor Collection
  • Involves screening and collecting blood for transfusion purposes, not mainly for testing.
  • Blood units used to address blood loss, hemorrhagic tendencies, or other needs.
  • Requires special training and venipuncture skills.
Technical Aspects
  • Needle Gauge: Uses a larger gauge needle (16 to 18) compared to routine phlebotomy (21 to 23).
    • Larger bore to collect approximately 450-550 ml of blood without complications like clotting or hemolysis.
  • Vein Selection: Requires a large antecubital vein due to the significant volume of blood needed.
  • Cleaning: Proper cleaning with povidone-iodine to maintain sterility.
    • Blood units are considered medicine/blood products and must be collected sterilely.
    • Povidone-iodine eradicates normal flora that could contaminate the blood product.
  • Anticoagulant and Preservative Solution: Contains CPD or CPDA-1 (Citrate, Phosphate, Dextrose).
    • Citrate: prevents clotting.
    • Phosphate: stabilizes pH to maintain RBC viability.
    • Dextrose: provides energy to cells to keep them viable.
Donor Eligibility
  • General requirements:
    • Feeling well and in good health.
    • Adequate sleep (8-10 hours).
    • At least 17 years old (or 16 with parental permission, depending on local laws).
    • Weigh at least 50 kilograms (ensures capability to donate 450 ml of blood).
    • Physician's discretion for donors over 60.
  • Brief physical examination by a physician (blood pressure, temperature, signs/symptoms of sickness).
  • Extensive medical history to identify reasons for deferral (temporary or permanent).
    • Reasons for deferral vary; refer to AABB website for detailed lists.
Collection Technique
  • Needle angle: Zero degrees (flat insertion) to avoid splashing due to the large bore.
  • Proper technique: Stretch skin, anchor the vein, clean the area.
  • Lock: Open the lock once blood flow is established.
Specimen Samples in Blood Banking
  • Blood banking involves more than just blood donation.
  • Crossmatching: Determines donor-patient compatibility.
  • Blood Typing: Forward and reverse methods.
    • Specimens: EDTA and red-top serum tubes (red-top preferred).
    • Positive testing indicated by agglutination (cell clumping).
  • Blood Products: Whole blood, packed RBCs, platelet concentrate, plasma.

Blood Cultures

Purpose
  • Detect bacteria or microorganisms in the bloodstream (systemic infection).
  • Normally, blood is sterile; infection can lead to sepsis.
  • Symptoms: fever, underlying conditions.
Procedure
  • Phlebotomist collects the sample.
  • Blood culture bottles are the number one order of draw to minimize contamination.
Identifying Organisms
  • Determines the extent of the infection (systemic or localized).
  • Identifies the specific organism to guide antibiotic selection.
  • Crucial due to antimicrobial resistance (organisms unaffected by antibiotics).
Terminology
  • Bacteremia: Bacteria in the blood.
  • Septicemia: Bacteria in the blood with other detrimental conditions present.
Specimen Requirements
  • Varies: two to four blood cultures or two sites (different arms).
  • Must be filled with optimal blood-to-broth ratio.
  • Specialized container: blood culture bottle with nutrients (broth) to keep bacteria alive.
    • The machine incubates bacteria at 37 degrees Celsius.
  • Different bottles for pediatric (at least 1 ml) and adult (at least 5 ml) patients.
Skin Antiseptics
  • Use povidone-iodine to prevent normal flora from interfering with testing.
  • Normal flora: microorganisms/bacteria living on the skin.
  • Antiseptics destroy microorganisms on the skin.
  • Apply antiseptic with friction for 30-60 seconds.
Motion of Cleaning
  • Controversy about motion: back and forth vs. circular.
  • By the book, technical for usual phlebotomy procedure superior and back and forth method. But for blood culture, the superior is concentric.
  • Clean with alcohol after iodine.
Media Inoculation Methods
  • Inoculation: adding blood to a media (culture bottle, broth, media plates) to grow bacteria.
  • Direct inoculation: directly into the culture bottle (bedside).
  • After collection: use a special intermediate collection tube for inoculation later in the laboratory.
Technique Reminders
  • Avoid backflow.
  • Mix the container after inoculation.
  • If using a metal cap, remove it and clean with alcohol.
  • For syringe inoculation, allow the vacuum to draw blood; do not push the plunger.
Intermediate Collection
  • SPS (Sodium Polyanethol Sulfonate) tubes: cannot be used for blood culture insert machine.
  • SPS acts as an anticoagulant and complement inhibitor to reduce the action of complement proteins.
  • Use culture bottles, you need to have direct inoculation.
Antimicrobial Removal Devices (ARD)
  • ARD neutralizes antibiotics to allow bacteria detection even if the patient is on antibiotics.
  • Most culture bottles already contain ARD; be aware of timing collections if ARD is not present.

Coagulation Specimens

Special Considerations
  • Use light blue top sodium citrate tubes.
  • If using a butterfly, draw a discard tube first to prime the tubing.
  • Maintain a 9:1 ratio of blood to anticoagulant.
  • Follow the manufacturer's lines for the volume of collection.
  • Never combine partially filled tubes.
  • If testing cannot occur within 4 hours, centrifuge and freeze the plasma.
  • Semi-automated and fully automated testing methods exist.

Two-Hour Postprandial Glucose (2-Hour PP)

Purpose
  • Evaluates the body's ability to regulate glucose levels after a meal.
  • Monitors insulin therapy.
  • Screens for diabetes and gestational diabetes.
Medical Technologist's Role
  • Ensure the patient follows procedures (meal intake, timing).
  • Timing is crucial due to reference values based on the two-hour interval.
  • Healthy individuals should have normalized glucose levels within the reference ranges.
Principles
  • Patient consumes a high-carbohydrate diet for 2-3 days before the test.

Oral Glucose Tolerance Test (OGTT)

Compared to 2-Hour PP
  • 2-hour PP: after a meal.
  • OGTT: glucose juice (50g, 75g, or 100g).
  • Method to diagnose carbohydrate metabolism disorders and monitor insulin response.
Reminders
  • The patient cannot vomit the juice; repeat the test if vomiting occurs.
  • Finish the glucose juice within five minutes.
  • No drinking or eating anything until the procedure is complete.
  • Collect blood before administering the juice.
  • Collect blood one hour and two hours after drinking the juice, depending on the physician's order.
GTT Preparation
  • Fast for at least 12 hours.
  • No drinking water, smoking, chewing gum.
  • Avoid strenuous exercises or exaggerated movements.

Lactose Tolerance Test

Procedure
  • Similar to OGTT, but replaces glucose with lactose/milk sugar.
  • Identifies lactose intolerance by testing for the enzyme lactase.

Molecular Genetic Testing

Overview
  • Analyzes DNA, RNA, chromosomes, and other biological materials.
  • Specimens: sterile whole blood (EDTA, white top), ACD, sodium citrate, or sodium heparin.
  • Also swabs, secretions, and body fluids.

Parental or Paternity Testing

Principles
  • DNA profiling/genetic fingerprinting determines the probability of genetic parent-child relationships.
  • Requires chain of custody.