Davis's Lab & Diagnostic Tests

Complete Blood Count, Hemoglobin

General

Synonym/Acronym:
Hgb.

Common Use:
To evaluate anemia, polycythemia, hydration status, and monitor therapy such as transfusion.

Specimen:
Whole blood from one full lavender-top (EDTA) tube, Microtainer, or capillary. Whole blood from a green-top (lithium or sodium heparin) tube may also be submitted.

Normal Findings:
(Method: Spectrophotometry)

AgeConventional UnitsSI Units (Conventional Units × 10)
Cord blood13.5–20.7 g/dL135–207 g/L
0–1 wk15.2–23.6 g/dL152–236 g/L
2–3 wk12.7–18.7 g/dL127–187 g/L
1–2 mo9.7–17.3 g/dL97–173 g/L
3–11 mo9.3–13.3 g/dL93–133 g/L
1–5 yr10.4–13.6 g/dL104–136 g/L
6–8 yr10.9–14.5 g/dL109–145 g/L
9–14 yr11.5–15.5 g/dL115–155 g/L
15 yr–adult
 Male13.2–17.3 g/dL132–173 g/L
 Female11.7–15.5 g/dL117–155 g/L
Older adult
 Male12.6–17.4 g/dL126–174 g/L
 Female11.7–16.1 g/dL117–161 g/L

Description

Hemoglobin (Hgb) is the main intracellular protein of erythrocytes. It carries oxygen (O2) to and removes carbon dioxide (CO2) from red blood cells (RBCs). It also serves as a buffer to maintain acid-base balance in the extracellular fluid. Each Hgb molecule consists of heme and globulin. Copper is a cofactor necessary for the enzymatic incorporation of iron molecules into heme. Heme contains iron and porphyrin molecules that have a high affinity for O2. The affinity of Hgb molecules for O2 is influenced by 2,3-diphosphoglycerate (2,3-DPG), a substance produced by anaerobic glycolysis to generate energy for the RBCs. When Hgb binds with 2,3-DPG, O2 affinity decreases. The ability of Hgb to bind and release O2 can be graphically represented by an oxyhemoglobin dissociation curve. The term shift to the left describes an increase in the affinity of Hgb for O2. Conditions that can cause this leftward shift include decreased body temperature, decreased 2,3-DPG, decreased CO2 concentration, and increased pH. Conversely, a shift to the right represents a decrease in the affinity of Hgb for O2. Conditions that can cause a rightward shift include increased body temperature, increased 2,3-DPG levels, increased CO2 concentration, and decreased pH.

Hgb levels are a direct reflection of the O2-combining capacity of the blood. It is the combination of heme and O2 that gives blood its characteristic red color. RBC counts parallel the O2-combining capacity of Hgb, but because some RBCs contain more Hgb than others, the relationship is not directly proportional. As CO2 diffuses into RBCs, an enzyme called carbonic anhydrase converts the CO2 into bicarbonate and hydrogen ions. Hgb that is not bound to O2 combines with the free hydrogen ions, increasing pH. As this binding is occurring, bicarbonate is leaving the RBC in exchange for chloride ions. (For additional information about the relationship between the respiratory and renal components of this buffer system, see monograph titled “Blood Gases.”)

Hgb is included in the complete blood count (CBC) and generally performed with a hematocrit (Hct). These levels parallel each other and are frequently used to evaluate anemia. Polycythemia is a condition resulting from an abnormal increase in Hgb, 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 of 4.3 to 4.9). There are some cultural variations in Hgb and Hct (H&H) values. After the first decade of life, the mean Hgb in African Americans is 0.5 to 1.0 g lower than in whites. Mexican Americans and Asian Americans have higher Hgb and H&H values than whites.

Indications

  • Detect hematological disorder, neoplasm, or immunological abnormality
  • Determine the presence of hereditary hematological abnormality
  • Evaluate known or suspected anemia and related treatment, in combination with Hct
  • Monitor blood loss and response to blood replacement, in combination with Hct
  • Monitor the effects of physical or emotional stress on the patient
  • Monitor fluid imbalances or their treatment
  • Monitor hematological status during pregnancy, in combination with Hct
  • Monitor the progression of nonhematological disorders, such as chronic obstructive pulmonary disease (COPD), malabsorption syndromes, cancer, and renal disease
  • Monitor 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:

  • Burns (related to dehydration; total blood volume is decreased, but RBC count remains the same)
  • Congestive heart failure (when the underlying cause is anemia, the body will respond by increasing production of RBCs; with a responding increase in Hct)
  • COPD (related to chronic hypoxia that stimulates production of RBCs and a corresponding increase in Hgb)
  • Dehydration (total blood volume is decreased, but RBC count remains the same)
  • Erythrocytosis (total blood volume remains the same, but RBC count is increased)
  • Hemoconcentration (same effect as seen in dehydration)
  • High altitudes (related to hypoxia that stimulates production of RBCs and therefore increases Hgb)
  • Polycythemia vera (abnormal bone marrow response resulting in overproduction of RBCs)
  • Shock

Decreased In:

  • Anemias (overall decrease in RBCs and corresponding decrease in Hgb)
  • Blood loss (acute and chronic) (overall decrease in RBC and corresponding decrease in Hct)
  • Bone marrow hyperplasia (bone marrow failure that results in decreased RBC production)
  • Carcinoma (anemia is often associated with chronic disease)
  • Cirrhosis (related to accumulation of fluid)
  • Chronic disease (anemia is often associated with chronic disease)
  • Fluid retention (dilutional effect of increased blood volume while RBC count remains stable)
  • Hemoglobinopathies (reduced RBC survival with corresponding decrease in Hgb)
  • Hemolytic disorders (e.g. hemolytic anemias, prosthetic valves) (reduced RBC survival with corresponding decrease in Hct)
  • Hemorrhage (acute and chronic) (overall decrease in RBCs and corresponding decrease in Hgb)
  • Hodgkin’s disease (bone marrow failure that results in decreased RBC production)
  • Incompatible blood transfusion (reduced RBC survival with corresponding decrease in Hgb)
  • Intravenous overload (dilutional effect)
  • Leukemia (bone marrow failure that results in decreased RBC production)
  • Lymphomas (bone marrow failure that results in decreased RBC production)
  • Nutritional deficit (anemia related to dietary deficiency in iron, vitamins, folate needed to produce sufficient RBCs; decreased RBC count with corresponding decrease in Hgb)
  • Pregnancy (related to anemia)
  • Renal disease (related to decreased levels of erythropoietin, which stimulates production of RBCs)
  • Splenomegaly (total blood volume remains the same, but spleen retains RBCs and Hgb reflects decreased RBC count)

Critical Findings


Adults & children

  • Less than 6.6 g/dL (SI: Less than 66 g/L)
  • Greater than 20 g/dL (SI: Greater than 200 g/L)

Newborns
  • Less than 9.5 g/dL (SI: Less than 95 g/L)
  • Greater than 22.3 g/dL (SI: Greater than 223 g/L)

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

High Hgb 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 from 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 Hgb. 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 Hgb. 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 cause a decrease in Hgb include those that induce hemolysis due to drug sensitivity or enzyme deficiency and those that result in anemia (see monograph titled “Complete Blood Count, RBC Count”).
  • Some drugs may also affect Hgb values by increasing the RBC count (see monograph titled “Complete Blood Count, RBC Count”).
  • The results of RBC counts may vary depending on the patient’s position: Hgb can decrease when the patient is recumbent as a result of hemodilution and can increase when the patient rises as a result of hemoconcentration.
  • Use of the nutraceutical liver extract is strongly contraindicated in iron-storage disorders, such as hemochromatosis, because it is rich in heme (the iron-containing pigment in Hgb).
  • A severe copper deficiency may result in decreased Hgb levels.
  • Cold agglutinins may falsely increase the mean corpuscular Hgb concentration (MCHC) and decrease the RBC count, affecting Hgb values. This can be corrected by warming the blood or replacing the plasma with warmed saline and repeating the analysis.
  • Leaving the tourniquet in place for longer than 60 sec can falsely increase Hgb levels by 2% to 5%.
  • 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.
  • Clotted or hemolyzed specimens must be rejected for analysis.
  • Care should be taken in evaluating the Hgb during the first few hours after transfusion or acute blood loss because the value may appear to be normal.
  • Abnormalities in the RBC size (macrocytes, microcytes) or shape (spherocytes, sickle cells) may alter Hgb values, as in diseases and conditions including sickle cell anemia, hereditary spherocytosis, and iron deficiency.
  • Lipemia will falsely increase the Hgb measurement, also affecting the mean corpuscular volume (MCV) and MCHC. This can be corrected by replacing the plasma with saline, repeating the measurement, and manually correcting the Hgb, MCH, and MCHC using specific mathematical formulas.

Nursing Implications 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 evaluating the amount of hemoglobin in the blood to assist in diagnosis and monitor therapy.
  • 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, 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.

Intratest

  • 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 tubes with the corresponding patient demographics, date, and time of collection. Perform a venipuncture; collect the specimen in a 5-mL lavender-top (EDTA) tube. 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

  • 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 increased Hgb if iron levels are also elevated. Educate the patient with abnormally elevated iron values, as appropriate, on the importance of reading food labels. Patients with hemochromatosis or acute pernicious anemia should be educated to avoid foods rich in iron. Iron absorption is affected by numerous factors that may enhance or decrease absorption regardless of the original content of the iron-containing dietary source (see monograph titled “Iron”). Iron levels in foods can be increased if foods are cooked in cookware containing iron. Consumption of large amounts of alcohol damages the intestine and allows increased absorption of iron. A high intake of calcium and ascorbic acid also increases iron absorption. Iron absorption after a meal is also increased by factors in meat, fish, and poultry.
  • Nutritional Considerations: Nutritional therapy may be indicated for patients with decreased Hgb. Iron deficiency is the most common nutrient deficiency in the United States. The Institute of Medicine’s Food and Nutrition Board suggests 8 mg as the daily recommended dietary allowance of iron for adult males and females age 51 to greater than 70 yr; 18 mg/d for adult females age 19 to 50 yr; 8 mg/d for adult males age 19 to 50 yr; 27 mg/d for pregnant females under age 18 through 50 yr; 9 mg/d for lactating females age 19 to 50 yr; 10 mg/d for lactating females under age 18 yr; 15 mg/d for female children age 14 to 18 yr; 11 mg/d for male children age 14 to 18 yr; 8 mg/d for children age 9 to 13 yr; 10 mg/d for children age 4 to 8 yr; 7 mg/d for children age 1 to 3 yr; 11 mg/d for children age 7 to 12 mo; and 0.27 mg/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. Patients at risk (e.g., children, pregnant women, women of childbearing age, and low-income populations) should be instructed to include in their diet foods that are high in iron, such as meats (especially liver), eggs, grains, green leafy vegetables, and multivitamins with iron. Educate the patient with abnormally elevated iron values, as appropriate, on the importance of reading food labels. Iron absorption is affected by numerous factors, enhancing or decreasing absorption regardless of the original content of the iron containing dietary source (see monograph titled “Iron”). Iron absorption is decreased by the absence (gastric resection) or diminished presence (use of antacids) of gastric acid. Phytic acids from cereals; tannins from tea and coffee; oxalic acid from vegetables; and minerals such as copper, zinc, and manganese interfere with iron absorption.
  • 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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