Complete Blood Count, RBC Indices


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Complete Blood Count, RBC Indices

Synonym/acronym: Mean corpuscular hemoglobin (MCH), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), red blood cell distribution width (RDW).

Common use

To evaluate cell size, shape, weight, and hemoglobin concentration. Used to diagnose and monitor therapy for diagnoses such as iron-deficiency anemia.

Specimen

Whole blood (1 mL) collected in a lavender-top (EDTA) tube.

Normal findings

(Method: Automated, computerized, multichannel analyzers)
AgeMCV (fL)MCH (pg/cell)MCHC (g/dL)RDWCVRDWSD
Cord blood107–11935–3931–3514.9–18.751–66
0–1 wk104–11629–4524–3614.9–18.751–66
2–3 wk95–11726–3826–3414.9–18.751–66
1–2 mo81–12525–3726–3414.9–18.744–55
3–11 mo78–11022–3426–3414.9–18.735–46
1–5 yr74–9424–3230–3411.6–14.835–42
6–8 yr73–9324–3232–3611.6–14.835–42
9–14 yr74–9425–3332–3611.6–14.837–44
15 yr–adult
 Male77–9726–3432–3611.6–14.838–48
 Female78–9826–3432–3611.6–14.838–48
Older adult
 Male79–10327–3532–3611.6–14.838–48
 Female78–10227–3532–3611.6–14.838–48
MCV = mean corpuscular volume; MCH = mean corpuscular hemoglobin; MCHC = mean corpuscular hemoglobin concentration; RDWCV = coefficient of variation in red blood cell distribution width; RDWSD = standard deviation in RBC distribution width index.

Description

Red blood cell (RBC) indices provide information about RBC size and hemoglobin content. The indices are derived from mathematical relationships between the RBC count, Hgb level, and Hct. RBC indices are frequently used to assist in the classification of anemias. The mean corpuscular volume (MCV) reflects the average size of circulating RBCs and classifies size as normocytic, microcytic (smaller than normal), and macrocytic (larger than normal). MCV is determined by dividing the Hct by the total RBC. The RDW is a measurement of cell size distribution. Many of the commonly used automated cell counters report the more sophisticated statistical indices, RDWCV and RDWCV instead of RDW. The RDWCV is an indication of variation in cell size over the circulating RBC population. The RDWSD is also an indicator of variation in RBC size, is not affected by the MCV as with the RDWCV index, and is a more accurate measurement of the degree of variation in cell size. Review of peripheral smears is used to corroborate findings from automated instruments. Excessive variations in cell size are graded from 1+ to 4+, with 4+ indicating the most severe degree of anisocytosis, or variation in cell size. Mean corpuscular hemoglobin (MCH or average amount of Hgb in RBCs) and mean corpuscular hemoglobin concentration (MCHC or average amount of Hgb per volume of RBCs) are used to measure hemoglobin content. Microscopic review of the peripheral smear can also be used to visually confirm automated values. Terms used to describe the hemoglobin content of RBCs are normochromic, hypochromic, and hyperchromic. The findings are also visually graded from 1+ to 4+. The MCH is determined by dividing the total hemoglobin by the RBC count. MCHC is determined by dividing total hemoglobin by hematocrit. (See “Complete Blood Count, Hemoglobin,” “Complete Blood Count, Hematocrit,” “Complete Blood Count, RBC Count,” and “Complete Blood Count, RBC Morphology and Inclusions.”)

This procedure is contraindicated for

    N/A

Indications

  • Assist in the diagnosis of anemia
  • Detect a hematological disorder, neoplasm, or immunological abnormality
  • Determine the presence of a hereditary hematological abnormality
  • Monitor the effects of physical or emotional stress
  • Monitor the progression of nonhematological disorders such as chronic obstructive pulmonary disease, malabsorption syndromes, cancer, and renal disease
  • Monitor the response to drugs or chemotherapy, and evaluate undesired reactions to drugs that may cause blood dyscrasias
  • Provide screening as part of a complete blood count (CBC) in a general physical examination, especially upon admission to a health-care facility or before surgery

Potential diagnosis

Increased in

    MCV

  • Alcoholism (vitamin deficiency related to malnutrition)
  • Antimetabolite therapy (the therapy inhibits vitamin B12 and folate)
  • Liver disease (complex effect on RBCs that includes malnutrition, alterations in RBC shape and size, effects of chronic disease)
  • Pernicious anemia (vitamin B12/folate anemia)
  • MCH

  • Macrocytic anemias (related to increased hemoglobin or cell size)
  • MCHC

  • Spherocytosis (artifact in measurement caused by abnormal cell shape)
  • RDW

  • Anemias with heterogeneous cell size as a result of hemoglobinopathy, hemolytic anemia, anemia following acute blood loss, iron-deficiency anemia, vitamin- and folate-deficiency anemia (related to a mixture of cell sizes as the bone marrow responds to the anemia and/or to a mixture of cell shapes due to cell fragmentation as a result of the disease)

Decreased in

    MCV

    Iron-deficiency anemia (related to low hemoglobin) Thalassemias (related to low hemoglobin)

    MCH

    Hypochromic anemias (related to low hemoglobin) Microcytic anemias (related to low hemoglobin)

    MCHC

    Iron-deficiency anemia (the amount of hemoglobin in the RBC is small relative to RBC size)

    RDW:

    N/A

Critical findings

    N/A

Interfering factors

  • Drugs and substances that may decrease the MCHC include styrene (occupational exposure).
  • Drugs that may decrease the MCV include nitrofurantoin.
  • Drugs that may increase the MCV include colchicine, pentamidine, pyrimethamine, and triamterene.
  • Drugs that may increase the MCH and MCHC include oral contraceptives (long-term use).
  • Diseases that cause agglutination of RBCs will alter test results.
  • Cold agglutinins may falsely increase the MCV and decrease the RBC count. This can be corrected by warming the blood or diluting the sample with warmed saline and then correcting the RBC count mathematically.
  • RBC counts can vary depending on the patient’s position, decreasing when the patient is recumbent as a result of hemodilution and increasing when the patient rises as a result of hemoconcentration.
  • The results of a CBC should be carefully evaluated during transfusion or acute blood loss because the body is not in a state of homeostasis and values may be misleading. Considerations for draw times after transfusion include the type of product, the amount of product transfused, and the patient’s clinical situation. Generally, specimens collected an hour after transfusion will provide an acceptable reflection of the effects of the transfused product. Measurements taken during a massive transfusion are an exception, providing essential guidance for therapeutic decisions during critical care.
  • Venous stasis can falsely elevate RBC counts; therefore, the tourniquet should not be left on the arm for longer than 60 sec.
  • Failure to fill the tube sufficiently (i.e., tube less than three-quarters full) may yield inadequate sample volume for automated analyzers and may be a reason for specimen rejection.
  • Hemolyzed or clotted specimens should be rejected.
  • Lipemia will falsely increase the hemoglobin measurement, also affecting the MCV and MCH.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in assessing RBC shape and size.
  • Obtain a history of the patient’s complaints, including a list of known allergens especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s gastrointestinal, hematopoietic, immune, and respiratory systems; symptoms; and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Note any recent procedures that can interfere with test results.
  • Obtain a list of the patient’s current medications including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture. An EDTA Microtainer sample may be obtained from infants, children, and adults for whom venipuncture may not be feasible. The specimen should be mixed gently by inverting the tube 10 times. The specimen should be analyzed within 24 hr when stored at room temperature or within 48 hr if stored at refrigerated temperature. If it is anticipated the specimen will not be analyzed within 24 hr, two blood smears should be made immediately after the venipuncture and submitted with the blood sample. Smears made from specimens older than 24 hr may contain an unacceptable number of misleading artifactual abnormalities of the RBCs, such as echinocytes and spherocytes, as well as necrobiotic white blood cells.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include biopsy bone marrow, CBC, CBC hematocrit, CBC hemoglobin, CBC RBC count, CBC RBC morphology and inclusions, CBC WBC count and differential, erythropoietin, ferritin, folate, Hgb electrophoresis, iron/TIBC, lead, reticulocyte count, sickle cell screen, and vitamin B12.
  • Refer to the Gastrointestinal, Hematopoietic, Immune, and Respiratory systems tables at the end of the book for related tests by body system.
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