PRACTICE POINTS: Monitoring Laboratory Values: Lymphocytes, Blood Urea Nitrogen, Creatinine, and Lipoproteins

This is a continuation in the series of articles on monitoring laboratory values. Refer to the table in the December 2008 issue as a quick reference tool.1

Lymphocytes are part of the body's immune system. T lymphocytes, which develop in the thymus, are involved in cell-mediated immunity, such as bacterial death and tumor immunity. B lymphocytes develop in the bone marrow and are responsible for humoral immunity. They synthesize immunoglobulins, which react to specific antigens.

Measurement of lymphocytes aids in the diagnosis of immunosuppression and autoimmunity. A decrease in the total lymphocyte count (TLC) and thus impaired immunity can result from decreased protein intake. Decreased levels have been associated with surgery, lupus, lymphoma, immunosuppressive agents, and immunodeficiency. Elevated levels of TLC occur in individuals who use alcohol, in smokers, and in persons with autoimmune disorders.

The TLC is determined by multiplying the percentage of lymphocytes by the white blood cells and then dividing by 100. The normal TLC is 2000 cells/µL. Typically, a TLC of 1500 to 1800 cells/µL denotes a mild deficiency; a TLC of 900 to 1500 cells/µL suggests a moderate deficiency; and a TLC less than 900 cells/µL indicates a severe deficiency. For the patient with a wound, check the TLC monthly.

Urea is a byproduct of protein metabolism and is excreted by the kidneys. Blood urea nitrogen (BUN) is an indicator of renal function and fluid status.

Elevated levels of urea, or uremia, have been associated with delayed wound healing. Causes of uremia include gastrointestinal bleeding, prerenal failure due to reduced blood flow to the kidneys or crush injuries, intrinsic renal failure due to glomerulonephritis or nephrotic syndrome, postrenal failure due to obstruction of the ureter or urethra by stones or tumor, nephrotoxic drugs (such as cyclosporin), diuretics, certain antibiotics, and salicylates. With declining renal function, certain medications and antibiotic doses will need to be lower to avoid toxic buildup. Decreased levels of urea result from overhydration, liver damage, malnutrition, and phenothiazide use. Patients should ingest 30 to 35 mL/kg/d of fluids.

The normal BUN ranges from 8 to 25 mg/dL. For the patient with a wound, BUN should be checked weekly.

Creatinine is a byproduct of muscle catabolism, which is filtered by the kidneys and is excreted in the urine. Like BUN, creatinine is also an indicator of renal function, fluid status/dehydration, and protein wasting. A slight increase in creatinine can result from hypovolemia, whereas elevations greater than 2.5 mg/dL are suggestive of renal failure. If BUN increases while creatinine does not, this indicates dehydration. If both values are increased, then renal failure is likely. The worsening of renal function leads to impaired wound healing. Medications that are metabolized/excreted through the kidneys may build up to toxic levels if kidney function is impaired. Other causes of increased creatinine include lupus, hypertension, diabetes, shock, leukemia, consumption of a diet rich in creatine, and use of cephalosporins, gentamicin, amphotericin, and barbiturates.

The normal creatinine level ranges from 0.6 to 1.4 mg/dL. Like its counterpart BUN, the level should be checked weekly in a patient who has a wound.

Lipoproteins, such as cholesterol and triglycerides, are lipids bound to protein absorbed in the intestines. Cholesterol is an important component of cell membranes, and bile acid and steroid hormone synthesis. Triglycerides are manufactured by the liver and provide energy to the heart and muscles. They are transported in blood as chylomicrons.

Hyperlipidemia is a risk factor for peripheral vascular disease and subsequent ulcer formation. Elevated cholesterol levels are associated with diabetes mellitus, hypothyroidism, atherosclerosis, excess dietary intake, family history, renal failure, alcoholism, and the use of certain medications (aspirin, steroids, sulfonamides, vitamins A and D, and oral contraceptives). Decreased values of cholesterol can be found in the presence of malnutrition, infection, hyperthyroidism, malabsorption, anemia, inflammation, and the use of neomycin, hypoglycemics, estrogens, and tetracycline.

Decreased levels of triglycerides are found in hyperthyroidism, protein malnutrition, vitamin C excess, and the use of metformin. Increased levels occur in hypothyroidism, nephritic syndrome, atherosclerosis, cirrhosis, diabetes, hypertension, excess dietary intake, alcoholism, family history, and oral contraceptive use.

The reference range for cholesterol is 100 to 200 mg/dL; the reference range for triglycerides is 100 to 200 mg/dL. For the patient with a wound, check cholesterol and triglyceride levels weekly along with the patient's nutritional status.

Source: Hess CT. Clinical Guide: Skin & Wound Care. 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005.

Reference

1. Hess CT. Mapping laboratory values in wound healing. Adv Skin Wound Care 2008;21:592. [Context Link]

Source :
Advances in Skin & Wound Care: The Journal for Prevention and Healing
April 2009
Volume 22 Number 4
Pages 192 - 192