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Reticulocytes Count

Reticulocytes are non nucleated, immature red blood cells (RBCs) that remain in the peripheral blood for 24 to 48 hours while maturing. They're generally larger than mature RBCs. In this test, reticulocytes in a whole blood sample are counted and expressed as a percentage of the total RBC count. Because the manual method of reticulocyte counting uses only a small sample, values may be imprecise and should be compared with RBC count or hematocrit.

Purpose

• To aid in distinguishing between hypoproliferative and hyperproliferative anemias.
• To help assess blood loss, bone mar­row response to anemia, and therapy for anemia.

Patient preparation

• Explain to the patient that this test is used to detect anemia or to monitor its treatment.
• Tell him that a blood sample will be taken. Explain who will perform the venipuncture and when.
• Reassure him that drawing a blood sample will take less than 3 minutes.
• Explain that he may feel slight discomfort from the tourniquet pressure and the needle puncture.
• If the patient is an infant or child, explain to the parents that a small amount of blood will be taken from the finger or earlobe.
• Withhold antimalarials, antipyretics, azathioprine, chloramphenicol, corticotropin, dactinomycin, furazolidone (from infants),levodopa, methotrexate, phenacetin, and sulfonamides, as needed. If such medications must be continued, note this on the laboratory slip.
• Inform the patient that food or fluids need not be restricted before the test.

Procedure and posttest care

• Perform a venipuncture, and collect the sample in a 7-mllavender-top tube.
• If a hematoma develops at the venipuncture site, apply warm soaks.
• Examine a stained smear of peripheral blood for the percentage of reticulocytes in relation to the number of RBCs present.
• Resume administration of medications withheld before the test.
• Monitor a patient with an abnormal reticulocyte count for trends or significant changes in repeated tests.

Precautions

• Completely fill the collection tube and invert it gently several times to mix the sample and the anticoagulant.
• Handle the sample gently to prevent hemolysis.

Reference values

Reticulocytes compose 0.5% to 2.5% of the total RBC count. In infants the normal reticulocyte count ranges from 2% to 5% at birth, decreasing to adult levels in I to 2 weeks.

Abnormal findings

A low reticulocyte count indicates hypoproliferative bone marrow (hypoplastic anemia) or ineffective erythropoiesis (pernicious anemia).

A high reticulocyte count indicates a bone marrow response to anemia caused by hemolysis or blood loss. The reticulocyte count may also increase after therapy for iron deficiency anemia or pernicious anemia.

Interfering factors

• Failure to use the proper anticoagulant or to adequately mix the sample and the anticoagulant.
• Prolonged tourniquet constriction (false-low or false-high).
• Azathioprine, chloramphenicol, dactinomycin, and methotrexate (possible false-low).
• Corticotropin, antimalarials, antipyretics, furazolidone (in infants), levo­dopa (possible false-high).
• Sulfonamides (possible false-low or false-high).
• Recent blood transfusion (possible false-low due to hemodilution.

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