General

Core Lab Study

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.

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.

Critical Findings and Potential Interventions

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

• Less than 28.5% (SI: Less than 0.28 volume fraction)
• Greater than 66.9% (SI: Greater than 0.67 volume fraction)

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

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.