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DEPARTMENTS: PRACTICE POINTS

Clinical Order Sets

Defining Laboratory Tests for Pressure Ulcers

Hess, Cathy Thomas BSN, RN, CWOCN

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Advances in Skin & Wound Care: April 2015 - Volume 28 - Issue 4 - p 192
doi: 10.1097/01.ASW.0000462590.41066.bf
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In the March Practice Points column, we reviewed the importance of developing and implementing clinical order sets. In this column, we will examine a number of laboratory tests and values that can help the clinician accurately manage a patient with a pressure ulcer. The culmination of this work can be organized into a clinical order set.

Albumin

Albumin is a protein that acts as a building block for cells and tissues. Because it is produced by the liver, albumin levels may be reduced in patients with liver disease. The albumin level is also diminished in patients with renal disease, malnutrition, severe burn wounds, and malabsorption syndromes. Adequate intake of protein and essential nutrients is necessary to ensure adequate production of albumin.

The albumin test is the basic screening tool for protein status and a gross indicator of nutritional status and fluid balance. Albumin has a half-life of 18 to 20 days, making it sensitive to long-term protein deficiencies. The lower the albumin level, the greater the risk of edema because albumin accounts for a large portion of the oncotic pressure of blood plasma.

The albumin value is directly related to the severity of the protein deficiency. The extent to which albumin is decreased can help predict the risk of pressure ulcer formation. Albumin levels less than 3.2 g/dL have been shown to correlate with increased morbidity and mortality in patients admitted to the critical care unit. Elevated levels can be found in patients with dehydration, vomiting, diarrhea, and multiple myeloma.

Prealbumin

Prealbumin, or transthyretin, is another type of protein produced by the liver. It has a half-life of 2 to 3 days, making it a better indicator of acute nutritional status changes than albumin. The level can be diminished in patients with liver disease, widespread tissue damage, malnutrition, protein wasting, or inflammation, as well as in patients taking estrogen or a hormonal contraceptive.

The lower the prealbumin level, the greater the risk of mortality. Prealbumin carries thyroxine and vitamin A throughout the body; thus, lower prealbumin levels decrease transport of these substances. Elevated prealbumin levels have been found in patients with Hodgkin disease and in those taking a steroid and a nonsteroidal anti-inflammatory drug.

Hemoglobin A1c

Hemoglobin A1c (A1C) is composed of hemoglobin A with a glucose molecule, which is attached through a process called glycosylation. It is an indicator of long-term glucose control, and its value depends on the amount of serum glucose available. The A1c is mainly used as a measure of the efficacy of diabetic therapy. An elevated A1c level carries the same implications as an elevated serum glucose level, including impaired wound healing and decreased ability to fight infection. A level greater than 8% increases the risk of long-term complications.

Glucose

Glucose is formed from dietary carbohydrates and is stored in the liver and muscles as glycogen. A fasting blood glucose level gives the best indication of overall glucose homeostasis. Insulin allows transport of glucose into the cells for storage as glycogen. Glucagon stimulates conversion of glycogen to glucose for use by the cells as energy. Hypoglycemia results from malnutrition, cirrhosis, alcoholism, and excess insulin. The serum glucose level is elevated in patients with diabetes mellitus, burns, crush injuries, or renal failure and in those using a steroid. A chronically elevated glucose level causes microvascular damage, which inhibits oxygen and nutrient perfusion and hampers wound healing. An elevated glucose level also affects polymorphonuclear lymphocytes, causing decreased chemotaxis, diapedesis, and phagocytosis, which in turn leads to a diminished ability to fight infection. Finally, an elevated glucose level is a risk factor for the development of arterial and neuropathic ulcers in patients with diabetes mellitus.

Complete blood count

A complete blood count (CBC) measures the number of red blood cells, white blood cells, total amount of hemoglobin in the blood, the fraction of the blood composed of red blood cells (hematocrit), and the mean corpuscular volume. It also provides information about the mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration, which are calculated from other measurements in the CBC. The platelet count is usually included in the CBC.

It is important to review these blood components because they map directly to the wound-healing process. For example, hemostasis occurs immediately after initial injury. The primary cell responsible for this function is the platelet, which causes the body to form a clot to prevent further bleeding. Platelets also release key cytokines, such as platelet-derived growth factor, which recruit cells to participate in later phases of healing. Without the proper platelet count, wound healing is delayed.

These and other tests, such as renal and liver function tests and electrolyte levels, should be monitored based on the care plan related to the clinical presentation of the patient and his/her wound.

Selected Reference

Hess CT. Clinical Guide: Skin and Wound Care. 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2012.
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