Davis's Lab & Diagnostic Tests

Complete Blood Count, RBC Count



Common Use:
To evaluate the number of circulating red cells in the blood toward diagnosing disease and monitoring therapeutic treatment. Variations in the number of cells is most often seen in anemias, cancer, and hemorrhage.

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

Normal Findings:
(Method: Automated, computerized, multichannel analyzers)

AgeConventional Units (106 cells/microL)SI Units (1012 cells/L) (Conventional Units × 1)
Cord blood3.61–5.813.61–5.81
0–1 wk4.51–7.014.51–7.01
2–3 wk3.71–6.113.71–6.11
1–2 mo3.11–5.113.11–5.11
3–11 mo3.01–5.013.01–5.01
1–5 yr3.81–5.013.81–5.01
6–8 yr3.91–5.113.91–5.11
9–14 yr3.91–5.613.91–5.61
15 yr–adult
Older adult


A component of the complete blood count (CBC), the red blood cell (RBC) count determines the number of RBCs per cubic millimeters (expressed as the number of RBCs per liter of blood according to the international system of units [SI]). Because RBCs contain hemoglobin (Hgb), which is responsible for the transport and exchange of oxygen, the number of circulating RBCs is important. Although the life span of the normal RBC is 120 days, other factors besides cell age and decreased production can cause decreased values; examples are abnormal destruction due to intravascular trauma caused by atherosclerosis or due to an enlarged spleen caused by leukemia. The main sites of RBC production in healthy adults include the bone marrow of the vertebrae, pelvis, ribs, sternum, skull, and proximal ends of the femur and humerus. The main sites of RBC destruction are the spleen and liver. Erythropoietin, a hormone produced by the kidneys, regulates RBC production. Normal RBC development and function are also dependent on adequate levels of vitamin B12, folic acid, and iron. A deficiency in vitamin E (α-tocopherol), which is needed to protect the RBC membrane from oxidizers, can result in increased cellular destruction. Polycythemia is a condition resulting from an abnormal increase in Hgb, hematocrit (Hct), and RBC count. Anemia is a condition resulting from an abnormal decrease in Hgb, Hct, and RBC count. Results of the Hgb, Hct, and RBC count should be evaluated simultaneously because the same underlying conditions affect this triad of tests similarly. The RBC count multiplied by 3 should approximate the Hgb concentration. The Hct should be within three times the Hgb if the RBC population is normal in size and shape. The Hct plus 6 should approximate the first two figures of the RBC count within 3 (e.g., Hct is 40%; therefore 40 + 6 = 46, and the RBC count should be 4.6 or in the range 4.3 to 4.9). (See monographs titled “Complete Blood Count, Hematocrit,” “Complete Blood Count, Hemoglobin,” and “Complete Blood Count, RBC Indices.”)


  • Detect a hematological disorder involving RBC destruction (e.g., hemolytic anemia)
  • Determine the presence of hereditary hematological abnormality
  • Monitor the effects of acute or chronic blood loss
  • Monitor the effects of physical or emotional stress on the patient
  • Monitor patients with disorders associated with elevated erythrocyte counts (e.g., polycythemia vera, chronic obstructive pulmonary disease [COPD])
  • Monitor the progression of nonhematological disorders associated with elevated erythrocyte counts, such as COPD, liver disease, hypothyroidism, adrenal dysfunction, bone marrow failure, 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 CBC in a general physical examination, especially upon admission to a health care facility or before surgery

Potential Diagnosis

Increased In:

  • Anxiety or stress (related to physiological response)
  • Bone marrow failure (initial response is stimulation of RBC production)
  • COPD with hypoxia and secondary polycythemia (related to chronic hypoxia that stimulates production of RBCs and a corresponding increase in RBCs)
  • Dehydration with hemoconcentration (related to decrease in total blood volume relative to unchanged RBC count)
  • Erythremic erythrocytosis (related to unchanged total blood volume relative to increase in RBC count)
  • High altitude (related to hypoxia that stimulates production of RBCs)
  • Polycythemia vera (related to abnormal bone marrow response resulting in overproduction of RBCs)

Decreased In:

  • Chemotherapy (related to reduced RBC survival)
  • Chronic inflammatory diseases (related to anemia of chronic disease)
  • Hemoglobinopathy (related to reduced RBC survival)
  • Hemolytic anemia (related to reduced RBC survival)
  • Hemorrhage (related to overall decrease in RBC count)
  • Hodgkin’s disease (evidenced by bone marrow failure that results in decreased RBC production)
  • Leukemia (evidenced by bone marrow failure that results in decreased RBC production)
  • Multiple myeloma (evidenced by bone marrow failure that results in decreased RBC production)
  • Nutritional deficit (related to deficiency of iron or vitamins required for RBC production and/or maturation)
  • Overhydration (related to increase in blood volume relative to unchanged RBC count)
  • Pregnancy (related to anemia; normal dilutional effect)
  • Renal disease (related to decreased production of erythropoietin)
  • Subacute endocarditis

Critical Findings

The presence of abnormal cells, other morphological characteristics, or cellular inclusions may signify a potentially life-threatening or serious health condition and should be investigated. Examples are the presence of sickle cells, moderate numbers of spherocytes, marked schistocytosis, oval macrocytes, basophilic stippling, nucleated RBCs (if the patient is not an infant), or malarial organisms.

Note and immediately report to the health-care provider (HCP) any critically increased or decreased values and related symptoms. Timely notification of critical values for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value, the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical value may require completion of a notification form with review by Risk Management.

Low RBC count leads to anemia. Anemia can be caused by blood loss, decreased blood cell production, increased blood cell destruction, or hemodilution. Causes of blood loss include menstrual excess or frequency, gastrointestinal bleeding, inflammatory bowel disease, or hematuria. Decreased blood cell production can be caused by folic acid deficiency, vitamin B12 deficiency, iron deficiency, or chronic disease. Increased blood cell destruction can be caused by a hemolytic reaction, chemical reaction, medication reaction, or sickle cell disease. Hemodilution can be caused by congestive heart failure, renal failure, polydipsia, or overhydration. Symptoms of anemia (due to these causes) include anxiety, dyspnea, edema, hypertension, hypotension, hypoxia, jugular venous distention, fatigue, pallor, rales, restlessness, and weakness. Treatment of anemia depends on the cause.

High RBC count leads to polycythemia. Polycythemia can be caused by dehydration, decreased oxygen levels in the body, and an overproduction of RBCs by the bone marrow. Dehydration by diuretic use, vomiting, diarrhea, excessive sweating, severe burns, or decreased fluid intake decreases the plasma component of whole blood, thereby increasing the ratio of RBCs to plasma, and leads to a higher than normal Hct. Causes of decreased oxygen include smoking, exposure to carbon monoxide, high altitude, and chronic lung disease, which leads to a mild hemoconcentration of blood in the body to carry more oxygen to the body’s tissues. An overproduction of RBCs by the bone marrow leads to polycythemia vera, which is a rare chronic myeloproliferative disorder that leads to a severe hemoconcentration of blood. Severe hemoconcentration can lead to thrombosis (spontaneous blood clotting). Symptoms of hemoconcentration include decreased pulse pressure and volume, loss of skin turgor, dry mucous membranes, headaches, hepatomegaly, low central venous pressure, orthostatic hypotension, pruritus (especially after a hot bath), splenomegaly, tachycardia, thirst, tinnitus, vertigo, and weakness. Treatment of polycythemia depends on the cause. Possible interventions for hemoconcentration due to dehydration include intravenous fluids and discontinuance of diuretics if they are believed to be contributing to critically elevated Hct. Polycythemia due to decreased oxygen states can be treated by removal of the offending substance, such as smoke or carbon monoxide. Treatment includes oxygen therapy in cases of smoke inhalation, carbon monoxide poisoning, and desaturating chronic lung disease. Symptoms of polycythemic overload crisis include signs of thrombosis, pain and redness in extremities, facial flushing, and irritability. Possible interventions for hemoconcentration due to polycythemia include therapeutic phlebotomy and intravenous fluids.

Interfering Factors

  • Drugs and substances that may decrease RBC count by causing hemolysis resulting from drug sensitivity or enzyme deficiency include acetaminophen, aminopyrine, aminosalicylic acid, amphetamine, anticonvulsants, antipyrine, arsenicals, benzene, busulfan, carbenicillin, cephalothin, chemotherapy drugs, chlorate, chloroquine, chlorothiazide, chlorpromazine, colchicine, diphenhydramine, dipyrone, glucosulfone, gold, hydroflumethiazide, indomethacin, mephenytoin, nalidixic acid, neomycin, nitrofurantoin, penicillin, phenacemide, phenazopyridine, and phenothiazine.
  • Drugs that may decrease RBC count by causing anemia include miconazole, penicillamine, phenylhydrazine, primaquine, probenecid, pyrazolones, pyrimethamine, quinines, streptomycin, sulfamethizole, sulfamethoxypyridazine, sulfisoxazole, suramin, thioridazine, tolbutamide, trimethadione, and tripelennamine.
  • Drugs that may decrease RBC count by causing bone marrow suppression include amphotericin B, floxuridine, and phenylbutazone.
  • Drugs and vitamins that may increase the RBC count include glucocorticosteroids, pilocarpine, and vitamin B12.
  • Use of the nutraceutical liver extract is strongly contraindicated in patients with iron-storage disorders such as hemochromatosis because it is rich in heme (the iron-containing pigment in Hgb).
  • Hemodilution (e.g., excessive administration of intravenous fluids, normal pregnancy) in the presence of a normal number of RBCs may lead to false decreases in RBC count.
  • Cold agglutinins may falsely increase the mean corpuscular volume (MCV) and decrease the RBC count. This can be corrected by warming the blood or diluting the sample with warmed saline and repeating the analysis.
  • Excessive exercise, anxiety, pain, and dehydration may cause false elevations in RBC count.
  • Care should be taken in evaluating the CBC after transfusion.
  • 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.
  • 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 must be rejected for analysis.

Nursing Implications Procedure


  • 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 for anemia and disorders affecting the number of circulating RBCs.
  • 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 cardiovascular, gastrointestinal, genitourinary, hematopoietic, hepatobiliary, 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).
  • 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.
  • There are no food, fluid, or medication restrictions unless by medical direction.


  • If the patient has a history of allergic reaction to latex, avoid the use of equipment containing 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 will contain an unacceptable number of misleading artifactual abnormalities of the RBCs, such as echinocytes and spherocytes, as well as necrobiotic WBCs.
  • 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

  • A report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Nutritional Considerations: Nutritional therapy may be indicated for patients with decreased RBC count. Iron deficiency is the most common nutrient deficiency in the United States. Patients at risk (e.g., children, pregnant women and women of childbearing age, low-income populations) should be instructed to include foods that are high in iron in their diet, such as meats (especially liver), eggs, grains, green leafy vegetables, and multivitamins with iron. Iron absorption is affected by numerous factors (see monograph titled “Iron”).
  • Nutritional Considerations: Patients at risk for vitamin B12 or folate deficiency include those with the following conditions: malnourishment (inadequate intake), pregnancy (increased need), infancy, malabsorption syndromes (inadequate absorption/increased metabolic rate), infections, cancer, hyperthyroidism, serious burns, excessive blood loss, and gastrointestinal damage. The Institute of Medicine’s Food and Nutrition Board suggests 2.4 mcg as the daily recommended dietary allowance of vitamin B12 for adult males and females age 19 to greater than 70 yr; 2.6 mcg/d for pregnant females less than age 18 through 50 yr; 2.8 mcg/d for lactating females less than age 18 through 50 yr; 2.4 mcg/day for children age 14 to 18 yr; 1.8 mcg/d for children age 9 to 13 yr; 1.2 mcg/d for children age 4 to 8 yr; 0.9 mcg/d for children age 1 to 3 yr; 0.5 mcg/d for children age 7 to 12 mo (recommended adequate intake); 0.4 mcg/d for children age 0 to 6 mo (recommended adequate intake). Reprinted with permission from the National Academies Press, copyright 2013, National Academy of Sciences. Instruct the patient with vitamin B12 deficiency, as appropriate, in the use of vitamin supplements. Inform the patient, as appropriate, that the best dietary sources of vitamin B12 are meats, milk, cheese, eggs, and fortified soy milk products. The Institute of Medicine’s Food and Nutrition Board suggests 400 mcg as the daily recommended dietary allowance of folate for adult males and females age 19 to greater than 70 yr; 600 mcg/d for pregnant females less than age 18 through 50 yr; 500 mcg/d for lactating females less than age 18 through 50 yr; 400 mcg/day for children age 14 to 18 yr; 300 mcg/d for children age 9 to 13 yr; 200 mcg/d for children age 4 to 8 yr; 150 mcg/d for children age 1 to 3 yr; 80 mcg/d for children age 7 to 12 mo (recommended adequate intake); 65 mcg/d for children age 0 to 6 mo (recommended adequate intake). Reprinted with permission from the National Academies Press, copyright 2013, National Academy of Sciences. Instruct the folate-deficient patient (especially pregnant women), as appropriate, to eat foods rich in folate, such as meats (especially liver), salmon, eggs, beets, asparagus, green leafy vegetables such as spinach, cabbage, oranges, broccoli, sweet potatoes, kidney beans, and whole wheat.
  • Nutritional Considerations: A diet deficient in vitamin E puts the patient at risk for increased RBC destruction, which could lead to anemia. Nutritional therapy may be indicated for these patients. The Institute of Medicine’s Food and Nutrition Board suggests 15 mg/d as the daily recommended dietary allowance for dietary vitamin E for adult males and females age 14 to greater than 70 yr; 15 mg/d for pregnant females less than age 18 through 50 yr; 12 mg/day for pregnant females age 14 to 18 yr; 19 mg/d for lactating females less than age 18 through 50 yr; 11 mg/day for children age 9 to 13 yr; 7 mg/d for children age 4 to 8 yr; 6 mg/d for children age 1 to 3 yr; 5 mg/d for children age 7 to 12 mo; 4 mg/d for children age 0 to 6 mo. Reprinted with permission from the National Academies Press, copyright 2013, National Academy of Sciences. Educate the patient with a vitamin E deficiency, if appropriate, that the main dietary sources of vitamin E are vegetable oils including olive oil), whole grains, wheat germ, nuts, milk, eggs, meats, fish, and green leafy vegetables. Vitamin E is fairly stable at most cooking temperatures (except frying) and when exposed to acidic foods. Supplemental vitamin E may also be taken, but the danger of toxicity should be explained to the patient. Very large supplemental doses, in excess of 600 mg of vitamin E over a period of 1 yr, may result in excess bleeding. Vitamin E is heat stable but is very negatively affected by light.
  • 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. Educate the patient regarding access to nutritional counseling services. Provide contact information, if desired, for the Institute of Medicine of the National Academies (www.iom.edu).
  • 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

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