Synonym/Acronym
Hgb and Hct, H&H.
Rationale
To evaluate anemia, polycythemia, hydration status, and monitor therapy such as transfusion.
A small group of studies in this manual have been identified as Core Lab Studies. The designation is meant to assist the reader in sorting the basic “always need to know” laboratory studies from the hundreds of other valuable studies found in the manual—a way to begin putting it all together.
Normal, abnormal, or various combinations of core lab study results can indicate that all is well, reveal a problem that requires further investigation with additional testing, signal a positive response to treatment, or suggest that the health status is as expected for the associated situation and time frame.
H&H is one of the most requested lab studies and is included in the Anemia profile, complete blood count, general health panel, hemolysis profile, and obstetric panel.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.
Normal Findings
Method: Spectrophotometry.
| Age | Conventional Units | SI Units | | |
|---|
| Hgb (g/dL) | Hct (%) | Hgb: SI Units g/L (Conventional Units × 10) | Hct: SI Units Volume Fraction (Conventional Units × 0.01) |
|---|
| Cord blood | 13.5–19.5 | 41–59 | 135–195 | 0.41–0.59 | | 0–1 wk | 14.5–22.5 | 44–68 | 145–225 | 0.44–0.68 | | 2–3 wk | 13.3–20.5 | 40–62 | 133–205 | 0.4–0.62 | | 1–2 mo | 10.7–18 | 31–55 | 107–180 | 0.31–0.55 | | 3–6 mo | 9–13.5 | 27–41 | 90–135 | 0.27–0.41 | | 7 mo–15 yr | 10.3–13.3 | 31–43 | 103–133 | 0.31–0.43 | | 16–18 yr | 11–15 | 33–45 | 110–150 | 0.33–0.45 | | Adult | | | | | | Male | 14–17.3 | 42–52 | 140–173 | 0.42–0.52 | | Female | 11.7–15.5 | 36–48 | 117–155 | 0.36–0.48 | | Pregnant female | | | | | | First trimester | 11.6–13.9 | 35–42 | 116–139 | 0.35–0.42 | | Second and third trimesters | 9.5–11 | 28–33 | 95–110 | 0.28–0.33 |
Values are slightly lower in older adults. Reference range values may vary between laboratories. |
Reference values for the Hgb and Hct vary across the age continuum and by gender. For example, the developing neonate has a very high demand for oxygen. Therefore, the RBC count and Hgb and Hct are also high. Also, in females, Hgb and Hct decrease when puberty begins while the same measurements increase at puberty in males. The difference between females and males can be partially explained by menstrual blood loss in females and the effects of androgens in males. Care must be taken when reviewing H&H values after a blood product transfusion—documentation should clearly reflect the time and date of the last transfusion with respect to the collection time of the study.
Hgb
Adults & children
- Less than 6.6 g/dL (SI: Less than 66 mmol/L)
- Greater than 20 g/dL (SI: Greater than 200 mmol/L)
Newborns
- Less than 9.5 g/dL (SI: Less than 95 mmol/L)
- Greater than 22.3 g/dL (SI: Greater than 223 mmol/L)
Hct
Adults & children
- Less than 19.8% (SI: Less than 0.2 volume fraction)
- Greater than 60% (SI: Greater than 0.6 volume fraction)
Newborns
Consideration may be given to verifying the critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory.
Low Hgb/Hct leads to anemia.
- Causes: Anemia can be caused by blood loss, decreased blood cell production, increased blood cell destruction, and hemodilution. Other 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 heart failure, chronic kidney disease, polydipsia, and overhydration.
- Symptoms: Symptoms of anemia (due to these causes) include anxiety, dyspnea, edema, fatigue, hypertension, hypotension, hypoxia, jugular venous distention, pallor, rales, restlessness, and weakness.
- Treatment: Treatment of anemia depends on the cause.
High Hgb/Hct leads to polycythemia.
- Causes: Polycythemia can be caused by dehydration, decreased oxygen levels in the body, and an overproduction of red blood cells (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 results in a severe hemoconcentration of blood. Severe hemoconcentration can lead to thrombosis (spontaneous blood clotting).
- Symptoms: 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: Treatment of polycythemia depends on the cause. Possible interventions for hemoconcentration due to dehydration include IV 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 IV fluids.
Study type: Blood collected in a lavender-top [EDTA] tube, Microtainer, or capillary; related body system: Circulatory/Hematopoietic system. Whole blood from a green-top [lithium or sodium heparin] tube may also be submitted.
Blood consists of a liquid plasma portion and a solid cellular portion. The solid portion is comprised of RBCs, WBCs, and platelets. It is important to be able to assess whether the number of circulating RBCs is sufficient to transport the required amount of oxygen throughout the body. The Hgb and Hct levels are part of the CBC. Frequently, Hgb and Hct measures are requested together as an H&H. H&H levels parallel each other and are the best determinant of the degree of anemia or polycythemia. Polycythemia is a term used in conjunction with conditions resulting from an abnormal increase in Hgb, Hct, and RBC counts. Anemia is a term associated with conditions resulting from an abnormal decrease in Hgb, Hct, and RBC counts.
Results of the Hgb, Hct, and RBC counts should be evaluated simultaneously because the same underlying conditions generally affect this triad of tests similarly.
- The RBC count multiplied by 3 should approximate the Hgb concentration +/–1.5 (e.g., RBC count is 5; therefore, Hgb is 5 × 3 = 15).
- The Hgb multiplied by 3 should approximate the Hct +/– 3 (e.g., Hgb is 15; therefore, Hct is 15 × 3 = 45).
- The rules of three only apply if the RBC population is normal in size and shape; they are valuable as a quality control check and warrant further investigation (issue with specimen, analyzer, or abnormal findings in patient specimen) if violated.
There are some ethnic variations in H&H values. After the first decade of life, the mean Hgb in
African Americans is 0.5 to 1 g lower than in individuals of European descent.
The Hct is a mathematical expression of the number of RBCs, or packed cell volume, expressed as a percentage of whole blood. For example, a packed cell volume, or Hct, of 45% means that a 100-mL sample of blood contains 45 mL of packed RBCs, which would reflect an acceptable level of RBCs for a patient of any given age. The Hct depends primarily on the number of RBCs; however, the average size of the RBCs influences Hct. Conditions that cause RBC size to be increased (e.g., swelling of the RBC due to change in osmotic pressure related to elevated sodium levels) may increase the Hct, whereas conditions that result in smaller than normal RBCs (e.g., microcytosis related to iron deficiency anemia) may decrease the Hct. Hct can be estimated directly by centrifuging a sample of whole blood for a specific time period. As the blood spins, it is separated into fractions. The RBC fraction is read against a scale. Most often, the Hct is measured indirectly by multiplying the RBC count and mean cell volume (MCV), using an automated cell counter. Hct can also be estimated by multiplying the Hgb by 3.
Hgb is the main intracellular protein of erythrocytes. It carries oxygen (O2) to and removes carbon dioxide (CO2) from 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 the study titled “Blood Gases.”)
Factors That May Alter the Results of the Study
- Drugs and other substances that may cause a decrease in Hgb and Hct include those that induce hemolysis due to drug sensitivity or enzyme deficiency and those that result in anemia (see the study titled “RBC Count, Indices, Morphology, and Inclusions”).
- Some drugs and other substances may also affect Hgb and Hct values by increasing the RBC count (see the study titled “RBC Count, Indices, Morphology, and Inclusions”).
- 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.
- Elevated blood glucose or serum sodium levels may produce elevated Hct levels because of swelling of the erythrocytes.
- Leaving the tourniquet in place for longer than 60 sec can falsely increase Hgb and Hct levels by 2% to 5%.
- The results of RBC counts may vary depending on the patient’s position: Hgb and Hct can decrease when the patient is recumbent as a result of hemodilution and can increase when the patient rises as a result of hemoconcentration.
Potential Nursing Problems: Assessment & Nursing Diagnosis
| Problems | Signs and Symptoms |
|---|
| Activity (related to decreased oxygen-carrying capacity of the blood secondary to anemia, decreased number of RBCs) | Weakness, fatigue, shortness of breath with activity, dizziness, palpitations, headache, verbalization of difficulty with activity tolerance | | Bleeding (related to bone marrow failure, cancer, GI bleed, trauma) | Altered level of consciousness, hypotension, increased heart rate, decreased Hgb and Hct, capillary refill greater than 3 sec, cool extremities | | Fatigue (related to decreased oxygenation associated with a decreased number of RBCs) | Verbalization of fatigue, altered ability to perform activities of daily living due to lack of energy, shortness of breath with exertion, increasingly frequent rest periods, presence of fatigue after sleep, inability to adhere to daily routine, altered level of concentration, reports of tiredness |
|
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
- Discuss how this test can assist in evaluating the amount of Hgb in the blood to assist in diagnosis and monitor therapy.
- Explain that a blood sample is needed for the test.
Potential Nursing Actions
Ensure informed consent for blood transfusion has been given and the consent signed prior to administration of blood or blood products. Follow organization protocol.
Safety Considerations
Ensure correct verification process by two licensed nurses prior to transfusion, or follow emergency protocol. Follow organization guidelines for safe administration.
After the Study: Implementation & Evaluation Potential Nursing Actions
Avoiding Complications
- Transfusion reaction may occur in some patients. Transfusion reaction is a critical finding. (See the study titled “Blood Typing, Antibody Screen, and Crossmatch” for information regarding transfusion reactions.)
Treatment Considerations
- Assess the color of the patient’s skin, as pallor is an indication of poor tissue perfusion.
- Frequently assess vital signs and explain to the patient that elevating the head of the bed may reduce difficulty in breathing.
- 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.
- The exception is a CBC taken during a massive transfusion, which provides essential guidance for therapeutic decisions (e.g., selection of blood products) during critical care.
Activity
- Assess for fall risk and implement strategies commensurate with level of risk.
- Administer prescribed oxygen and use pulse oximetry with visual assessment to evaluate effectiveness.
- Coordinate episodes of activity with rest periods and increase activity gradually as anemia resolves.
Bleeding
- Monitor and trend H&H and platelet count.
- Increase frequency of vital signs and monitor and trend results.
- Administer ordered blood products and monitor for transfusion reaction.
- Administer ordered stool softeners.
- Monitor and assess stool, urine, sputum, gums, and nose for blood.
- Coordinate laboratory draws to decrease frequency of venipuncture.
- Institute bleeding precautions: avoid intramuscular injections, prevent trauma, be gentle with oral care and suctioning, and avoid use of a sharp razor.
- Administer prescribed medications and assess diet for iron- and vitamin K–rich foods. Educate the patient regarding access to nutritional counseling services with a registered dietitian.
Fatigue
- Monitor and trend CBC, Hgb, and Hct.
- Administer ordered oxygen and assesses effectiveness with pulse oximetry and visual assessment.
- Monitor for shortness of breath.
- Assess nutritional intake.
- Assess ability to perform self-care, encourage frequent rest periods, prioritize and bundle activities to decrease fatigue, and teach techniques for conserving energy expenditure.
- Administer blood, blood products, and erythropoietin.
- Assess for medical or psychological factors contributing to fatigue.
Safety Considerations
- Follow all safety precautions to ensure transfused blood is a correct match for the patient.
Nutritional Considerations
- Nutritional therapy may be indicated for patients with increased Hgb and Hct if iron levels are also elevated.
- Provide education for those 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 the study titled “Iron Studies: Iron (Total), Iron-Binding Capacity (Total), Transferrin, and Iron Saturation”).
- 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 therapy may be indicated for patients with decreased Hgb and Hct, which may indicate corresponding iron deficiency.
- Iron deficiency is the most common nutrient deficiency in the United States.
- Those 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.
- Note: Animal liver (e.g. beef, chicken, deer, lamb) is a nutrient dense food. Micronutrients, with the exception of vitamin D, are not produced by the body; they must be obtained from dietary sources. Liver is a rich source of vitamins and minerals, most notably providing significant amounts of iron, copper, folate, vitamin A, and vitamin B12. Regularly eating large amounts of animal liver can result in vitamin A toxicity and/or damage to the patient’s liver. The general recommendation commonly given by health care providers to adult patients is to consume no more than one to three and a half ounces (28 to 100 gm) of liver, once a week. Recommended portions depend on age and gender. Patients should also be aware of vitamin and mineral concentrations contained in dietary supplements that are taken regularly.
- Provide instruction in the administration of iron supplements, including adverse effects, as appropriate.
- The goal of oral iron supplementation is to increase iron levels by about 1 g/dL (SI: 10 g/L) after 3 to 4 wk.
- Provide education for those with abnormally decreased Hgb values, as appropriate, about the importance of reading food labels and of dietary inclusion of iron-rich foods.
- Iron absorption is affected by numerous factors that may enhance or decrease absorption regardless of the original content of the iron-containing dietary source.
- Iron absorption is decreased by the absence (gastric resection) or diminished presence (use of antacids) of gastric acid.
Clinical Judgement
- Consider how to address cultural and religious barriers to the transfusion of blood and blood products.
Follow-Up and Desired Outcomes
- Acknowledges contact information provided for the U.S. Department of Agriculture’s resource for nutrition (www.choosemyplate.gov).
- States understanding of the risks and benefits associated with blood transfusion.
- Adheres to the request to include dietary foods high in iron.