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Hematocrit Lab

(Simulation)

Background Info

A. Test description and uses.

The hematocrit (HCT) measures the percentage of red blood cells (RBCs; erythrocytes) in a blood sample and is an essential clinical index that provides invaluable information on the patient’s health.

Conditions that lower the HCT.

(A) A low RBC count due to …

  • Bleeding.
  • Anemias.
    • Iron-deficiency.
    • Vitamin B12 deficiency.
    • Folic acid deficiency.
  • Leukemia or lymphoma.
  • Kidney disease.

(B) A high plasma level due to …

  • Water intoxication.
  • Retention of fluids.
    • Pregnancy.
    • Congestive heart failure.
    • Kidney disease.
    • High sodium intake.
    • Catabolic steroids.
Conditions that raise the HCT.

(A) A high RBC count (polycythemia) due to …

  • Hypoxia (reduced oxygen) induced RBC production.
    • Living at high altitudes.
    • Chronic obstructive pulmonary disease (COPD).
    • Emphysema and other lung diseases.
  • Testosterone supplement therapy.
  • Blood doping or erythropoietin (EPO).
  • Anabolic steroids.
  • Polycythemia vera – bone marrow abnormality.

(B) A low plasma level due to …

  • Dehydration.
  • Capillary leak syndrome.

In a well-equipped lab, an automated (computerized) analyzer is often used to calculate the hematocrit. The analyzer determines the value by multiplying the red cell count by the mean cell volume (MCV). For this lab, the HCT will be measured directly using centrifugation that separates the plasma from the packed RBCs.

B. Test subject’s history.

  • Male.
  • Age: 27.
  • Recently moved.
    to Denver, CO.
  • Exercises regularly.
  • Well-balanced diet.
  • Good health.

Test Procedures

A. Lance subject’s finger.

Allow a large drop of blood to accumulate on the surface of the finger.

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B. Draw blood into glass tube.

Place one end of the glass tube into the drop of blood on the finger surface. The blood will flow into the tube by capillary attraction. Heparin, an anticoagulant, keeps the blood from clotting after making contact with the glass tube.

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C. Seal tube with clay.

Stick the blood end of the micro-hematocrit tube into the clay sealer. The clay will prevent the blood from draining out of the tube while it is being centrifuged.

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D. Centrifuge blood sample.

After sealing the blood sample, place the tube in a micro-hematocrit centrifuge and spin it for a short period (actual settings = 10,000 for 5 minutes). The centripetal force caused by the spinning centrifuge will separate the blood into its component parts.

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E. Remove tube and examine layers.

The blood components typically separate into three distinct layers.

  • Red blood cells, the heaviest blood components, form a dark red column at the bottom of the tube.
  • White blood cells (WBCs; leukocytes) and platelets (thrombocytes) form a thin layer, called the buffy coat, directly above the RBCs.
  • Blood plasma, a pale, straw-colored fluid, fills the hematocrit tube above the buffy coat.
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F. Determine the hematocrit value.

A hematocrit reader card is used to determine the percentage of RBCs in the blood sample or packed cell volume (PCV). First, the glass tube is positioned on the left side of the reader card, with the bottom of the RBC column on the 0% line. Then, the glass tube is moved across the reader card until the top of the plasma column reaches the 100% line. The percentage of RBCs is then determined from the markings on the reader card.

  • Male normal value = about 45% (40% – 50%);
  • Female normal value = about 40% (36% – 44%).
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Analyze Results

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