section name header

Introduction ⬇

The word hematocrit means “to separate blood,” which underscores the mechanism of the test because the plasma and blood cells are separated by centrifugation.

The Hct test is part of the CBC. This test indirectly measures the RBC mass. The results are expressed as the percentage by volume of packed RBCs in whole blood (packed cell volume [PCV]). It is an important measurement in the determination of anemia or polycythemia.

Normal Findings ⬆ ⬇

Women: 36%–48%

Men: 42%–52%

Children:

Clinical Alert

An Hct 20% can lead to cardiac failure and death; an Hct >60% is associated with spontaneous clotting of blood

Procedure ⬆ ⬇

  1. Observe standard precautions. Obtain a 5-mL whole blood specimen in a lavender-topped tube (with EDTA). When doing a capillary puncture (finger puncture), the microcapillary tube is filled three-fourths full with blood directly from the puncture site. These tubes are coated with an anticoagulative. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered.

  2. Centrifuge the tubes in a microcentrifuge and measure the height of packed cells in the tube.

  3. Record the measurement as a percentage of the total amount of blood in the capillary tube.

  4. An Hct can be done on automated hematology instruments, in which case a 5-mL EDTA-anticoagulated venous blood sample is obtained.

Clinical Implications ⬆ ⬇

  1. Decreased Hct values are an indicator of anemia, a condition in which there is a reduction in the PCV. An Hct less than 30% means that the patient is moderately to severely anemic. Decreased values also occur in the following conditions:

    1. Leukemias, lymphomas, Hodgkin disease, myeloproliferative disorders

    2. Adrenal insufficiency

    3. Chronic disease

    4. Acute and chronic blood loss

    5. Hemolytic reaction: This condition may be found in transfusion of incompatible blood or as a reaction to chemicals or drugs, infectious agents, or physical agents (e.g., severe burns, prosthetic heart valves).

  2. The Hct may or may not be reliable immediately after even a moderate loss of blood or immediately after transfusion.

  3. The Hct may be normal after acute hemorrhage. During the recovery phase, both the Hct and the RBC count drop markedly.

  4. Usually, the Hct parallels the RBC count when the cells are of normal size. As the number of normal-sized erythrocytes increases, so does the Hct.

    1. However, for the patient with microcytic or macrocytic anemia, this relationship does not hold true.

    2. If a patient has iron-deficiency anemia with small RBCs, the Hct decreases because the microcytic cells pack to a smaller volume. The RBC count, however, may be normal or higher than normal.

  5. Increased Hct values occur in:

    1. Erythrocytosis

    2. Polycythemia vera

    3. Shock, when hemoconcentration rises considerably

Clinical Alert

Note that the same underlying conditions cause an increase or decrease in Hct, Hb, and RBC values

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure. Assess for signs/symptoms of fatigue, cool extremities, dyspnea, tachycardia, and pallor.

  2. Refer to standard pretest care for CBC and differential count. Also, follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed.

  2. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Monitor for anemia or polycythemia.

  3. Possible treatments may include administration of whole blood products, iron supplements, and proper nutrition. Also, supplemental oxygen may be ordered.

  4. Refer to standard posttest care for CBC and differential count. Also, follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. People living at high altitudes have high Hct values as well as high Hb and RBC values.

  2. Normally, the Hct slightly decreases in the physiologic hydremia of pregnancy.

  3. The normal values for Hct vary with age and gender. The normal value for infants is higher because the newborn has many macrocytic red cells. Hct values in females are usually slightly lower than in males.

  4. There is also a tendency toward lower Hct values in men and women older than 60 years, corresponding to lower RBC count values in this age group.

  5. Severe dehydration from any cause falsely raises the Hct.