Pearls of Knowledge: Anemia and Hydration

pearls of knowledge

Lab Values: Anemia and Hydration

Pearls of Knowledge © BrainyNurses.com

The CBC with differential is a frequently ordered lab test and provides much information regarding infection, anemia, coagulation, and hydration. When bone marrow suppression occurs, low levels of red blood cells, white blood cells, and platelets will be seen.

Monitoring anemia

Anemia is seen frequently in many different types of patients. When the red blood cells are low, pallor will be seen. If the red blood cells are too numerous, such as in polycythemia vera, the blood is “thicker” and there is a risk for blood clotting and myocardial dysfunction due to the strain.

Men have a higher red blood cell count mostly due to hormonal differences which stimulate higher hemoglobin production and greater muscle mass. For ease in clinical practice, it is helpful to remember the normal level for hemoglobin for everyone is 12-18 g/dL. Using the memory hint below, the normal RBC and hematocrit levels are easy to remember.

A critical hemoglobin level is less than 5.0 g/dL. When the level is < 7.0 g/dL, cardiac output increases to compensate, and a bounding pulse is present. As cardiac output falls, a weak pulse will be present, the pulse pressure will narrow, and signs of shock will develop. When anemia is present, the bone marrow releases reticulocytes, which then mature in the blood or spleen with the help of folic acid and B₁₂. A high reticulocyte count can be seen in several conditions, including acute or chronic blood loss and any pathology causing hemolysis of the red blood cells.

Anemia can be caused by increased blood loss, decreased production due to nutritional deficits or bone marrow suppression, or increased destruction due to genetically abnormal hemoglobin or antibodies. With hemolysis of the red blood cells, the bilirubin level will increase (> 1.2 mg/dL) and the spleen will enlarge.

The red blood cell indices reported on the CBC indicates how the cells are formed and helps to detect the type of anemia. Morphology of the cells is also evaluated to determine types, such as sickle cell.

Mean corpuscular volume (MCV)

Size of the cells.
Small and large cells may be present at the same time.

Red blood cell distribution width (RDW)

Similarity of size.
Microcytic may be due to lead poisoning or iron deficiency.
Macrocytic usually indicates lack of B₁₂ and folate as seen in pernicious anemia.
Macrocytic may also be seen in aplastic anemia or hypothyroidism.

Mean corpuscular hemoglobin concentration (MCHC)

Average amount of hemoglobin per red blood cell.
Low in hypochromic anemia.
High in macrocytic anemia.

Types of anemia

Hypochromic

Also known as iron deficiency anemia.
Most common type found in the elderly due to nutritional deficits.

Pernicious

Caused by the lack of intrinsic factor from gastritis, gastric surgery, or problems with the ileum, the inability to absorb B₁₂, and a shorter life span for the RBCs.
B₁₂ injections are needed for the lifespan.

Aplastic

Malfunctioning of the bone marrow caused by exposure to environmental chemicals, congenital abnormalities, or secondary to other
In some cases, a bone marrow transplant may be needed.

Sickle cell (hemolytic)

Caused by an abnormality in hemoglobin S.
Numerous conditions can trigger a sickle cell crisis which is an acute occlusion which can last for 4-6 days.

Thalassemia (hemolytic)

Most prominent in Black, Asian, and Mediterranean cultures.
Specific facial features such as wide set eyes, flattened nose, and maxillary prominence will be seen.
In addition to spleen enlargement, liver enlargement may also occur.

Erythroblastosis fetalis (hemolytic)

The destruction of neonatal red blood cells due to Rh incompatibility.
Bone marrow transplant and immunosuppression drugs may be needed

Platelet count

Platelet are produced in the bone marrow and is the first part of the coagulation cascade. Thrombocytopenia results when too few platelets are produced, or the platelets are destroyed. The lower the value, the more dangerous for the patient.

Normal count 150,000-400,000 mm³.
< 80,000 mm3, implement bleeding precautions.
< 50,000 mm³, give a transfusion before a major surgery or invasive procedure
< 20,000 mm3, high risk for
< 10,000 mm3, high risk for cerebral and pulmonary

Monitoring hydration

Based on the Memory Hint, hematocrit should be three times the hemoglobin. In anemia both values will be low. Hematocrit is used to determine hydration status in conjunction with BUN, creatinine, sodium, and specific gravity. Look at these three clinical correlations to determine the hydration status.

Clinical correlation #1

A patient is admitted with hyperosmolar hyperglycemic syndrome. His hemoglobin is 12 g/dL and the hematocrit is 47%.

The hematocrit is elevated in relation to the hemoglobin, signifying dehydration.

Clinical correlation #2

A patient is 4 days post-op from a bowel resection and his IV is running at 125 mL/hr. His hemoglobin is 12 g/dL and the hematocrit is 27%.

The hematocrit is low in relation to the hemoglobin, signifying over hydration.

Clinical correlation #3

A patient with gastroenteritis presents with vomiting and diarrhea for the past three days. His hemoglobin is 10 g/dL and the hematocrit is 33%.

The hemoglobin is low, signifying anemia. The hematocrit is high in relation to the hemoglobin, signifying dehydration.

Summary

So, the next time you look at a CBC, consider the following:

RBC and hemoglobin for the presence of anemia or overproduction of cells.

The presence of reticulocytes.

Type of anemia based on the indices and the clinical history.

If a hemolytic type, look at the bilirubin level.

Determine the hydration status.