**Understanding Laboratory Testing and Results

Laboratory testing plays a vital role in diagnosing, monitoring, and treating patients. As a phlebotomist, you are the first link in the testing chain. This section will introduce the types of tests you will frequently encounter. The quality of the sample you collect is paramount to accurate results. Errors in the pre-analytical phase (before the test is actually run) can significantly affect the outcome. It's crucial to understand the purpose of each test, the specific requirements for sample collection (e.g., tube type, order of draw), and the potential factors that can influence the results. Understanding normal ranges and critical values is key to recognizing potentially life-threatening situations.

The CBC is one of the most frequently ordered tests. It provides information about the different blood cells.

• Purpose: Evaluates overall health and detects a wide range of conditions, including anemia, infections, and leukemia.

• Components:

  • White Blood Cells (WBC): Measures the number of infection-fighting cells.
    • Normal Range: 4,500 - 11,000/µL
    • Elevated (Leukocytosis): Suggests infection, inflammation, or leukemia.
    • Decreased (Leukopenia): Suggests viral infections, bone marrow disorders, or certain medications.
  • Red Blood Cells (RBC): Measures the number of red blood cells, which carry oxygen.
    • Normal Range (Men): 4.5 - 5.5 million/µL
    • Normal Range (Women): 4.0 - 5.0 million/µL
    • Elevated (Polycythemia): Can be caused by dehydration, smoking, or certain medical conditions.
    • Decreased (Anemia): Indicates a lower-than-normal red blood cell count.
  • Hemoglobin (Hgb): Measures the oxygen-carrying protein in red blood cells.
    • Normal Range (Men): 13.5 - 17.5 g/dL
    • Normal Range (Women): 12.0 - 16.0 g/dL
    • Decreased: Can indicate anemia or bleeding.
  • Hematocrit (Hct): Measures the percentage of red blood cells in the total blood volume.
    • Normal Range (Men): 40 - 50%
    • Normal Range (Women): 36 - 48%
  • Platelets (PLT): Measures the number of cells involved in blood clotting.
    • Normal Range: 150,000 - 450,000/µL
    • Elevated (Thrombocytosis): Can be caused by infection, inflammation, or certain cancers.
    • Decreased (Thrombocytopenia): Can indicate bleeding disorders, medications, or autoimmune diseases.

• Critical Values: Significantly abnormal results require immediate notification to a healthcare provider. Examples include a very low hemoglobin level (e.g., <8 g/dL) or a very high or very low WBC count.

The CMP is a comprehensive test that assesses various aspects of organ function and metabolism.

• Purpose: Evaluates kidney function, liver function, electrolyte balance, and blood glucose levels.

• Components (Key):

  • Glucose: Measures blood sugar levels.
    • Normal Range (Fasting): 70 - 100 mg/dL
    • Elevated (Hyperglycemia): Suggests diabetes or pre-diabetes.
    • Decreased (Hypoglycemia): Indicates low blood sugar.
  • Kidney Function:
    • BUN (Blood Urea Nitrogen): Measures waste products filtered by the kidneys.
      • Normal Range: 7 - 20 mg/dL
    • Creatinine: Measures waste products filtered by the kidneys.
      • Normal Range: 0.6 - 1.2 mg/dL (Men), 0.5 - 1.1 mg/dL (Women)
  • Electrolytes:
    • Sodium (Na+): Critical for fluid balance.
      • Normal Range: 135 - 145 mEq/L
    • Potassium (K+): Important for heart function.
      • Normal Range: 3.5 - 5.0 mEq/L
  • Liver Function:
    • AST (Aspartate Aminotransferase) / ALT (Alanine Aminotransferase): Enzyme levels which can indicate liver inflammation.
    • Total Bilirubin: Can indicate liver or gallbladder problems.

• Critical Values: Markedly elevated or decreased electrolytes (e.g., potassium > 6.0 mEq/L or < 2.5 mEq/L), significantly abnormal glucose levels (e.g., <40 mg/dL or >400 mg/dL).

The lipid panel assesses the levels of fats in the blood, used to evaluate the risk of cardiovascular disease.

• Purpose: Evaluates the risk of heart disease.
• Components:
  • Total Cholesterol: All forms of cholesterol in the blood.
    • Desirable: Less than 200 mg/dL
    • High: 240 mg/dL and above
  • LDL Cholesterol (Low-Density Lipoprotein): Often called "bad" cholesterol.
    • Optimal: Less than 100 mg/dL (Ideal for patients with heart disease or high risk).
    • High: 160 mg/dL and above (High risk).
  • HDL Cholesterol (High-Density Lipoprotein): Often called "good" cholesterol.
    • Desirable: 60 mg/dL and above
    • Low: Less than 40 mg/dL (Risk factor)
  • Triglycerides: Another type of fat in the blood.
    • Normal: Less than 150 mg/dL
    • High: 200 mg/dL and above
• Patient Preparation: Patients typically need to fast (no food or drink other than water) for 9-12 hours before the test for accurate results.

Coagulation studies evaluate the blood's ability to clot.

• Purpose: Assess for bleeding disorders or to monitor anticoagulant therapy.

• Components:

  • PT (Prothrombin Time): Measures how long it takes for blood to clot.
    • Normal Range: 11-13.5 seconds
    • Used to monitor warfarin (Coumadin) therapy.
  • INR (International Normalized Ratio): Standardized way to report PT results.
    • Normal Range: 0.8-1.2 (for patients not on anticoagulants)
    • Therapeutic Range (for patients on warfarin): Varies based on indication, often 2.0-3.0.
  • PTT (Partial Thromboplastin Time): Evaluates the other clotting factors.
    • Normal Range: 25-35 seconds
    • Used to monitor heparin therapy.

• Patient Preparation: No special preparation is typically required, but it's important to note if the patient is taking blood-thinning medications.

Many factors can influence the accuracy of lab results. As a phlebotomist, you can play a critical role in preventing inaccurate results.

• Patient Preparation: Ensure patients follow pre-test instructions (e.g., fasting for lipid panels, avoiding strenuous exercise). Improper preparation can significantly alter results. You must verify if the patient has followed the preparation instructions.
• Medications: Some medications can affect test results. Always ask the patient about any medications they are taking and document this information. Communicate with the nurse or physician, if necessary.
• Specimen Collection: Correct tube selection, order of draw, and proper venipuncture technique are essential.
  • Hemolysis: Rupture of red blood cells during collection can falsely elevate certain results (e.g., potassium, AST). Avoid by using the correct needle size, not forcing blood into the tube, and properly mixing the tubes.
  • Clotting: Not mixing the blood in the tube immediately after collection can cause clotting, leading to inaccurate results.
• Patient Position: Prolonged standing or lying down can slightly affect some results. Document the patient’s position during the draw.

Your role extends beyond just drawing blood. You are responsible for ensuring specimen integrity and accurate results.

• Patient Identification: Verify patient identification using two identifiers (name, date of birth, medical record number) to prevent misidentification.
• Tube Selection: Select the correct tubes based on the test order, and understand the order of draw.
• Proper Technique: Use proper venipuncture technique to avoid hemolysis.
• Labeling: Label tubes accurately and completely at the patient's bedside, including patient name, date, time of collection, and your initials.
• Specimen Handling: Handle and transport specimens according to laboratory protocols.
• Communication: Communicate any unusual findings or difficulties with collection to the laboratory or nurse. Report potential issues to the appropriate personnel.