V

Vanillylmandelic acid

See Catecholamines, Urinary on pp. 182.

Varicella-zoster antibody

Also called: VZV Antibody

Specimen or type of test:

Blood

Purpose of the test

The immunoglobulin IgM antibody test occasionally is used to identify the current infection with the varicella-zoster virus. The immunoglobulin IgG antibody test is used to confirm past infection or vaccination that provides immunity from future chickenpox infection.

Basics the nurse needs to know

The varicella-zoster virus is a herpesvirus that causes the primary infection of varicella (chickenpox) and years later can cause the reactivated infection of shingles (herpes zoster infection). A negative result for varicella-zoster antibodies means that the person has no immunity from chickenpox and is susceptible to acquire this infection. If a person has positive IgG antibodies or a high IgG titer, it means there is immunity to future chickenpox infection, but there may not be immunity to shingles.

In the acute illness phase, the IgM antibody test becomes positive 1 to 3 days after the skin eruption occurs. In the convalescent phase, the IgG antibody becomes positive 9 to 10 days after the skin eruption occurs. If the pregnant woman contracts this infection in the last 3 weeks of pregnancy, the fetus may develop chickenpox. Positive IgM antibodies in the amniotic fluid or cord blood means that the fetus has a varicella infection.

Antibody testing is done in the pretransplant patient. If there is no immunity to varicella-zoster, vaccination will be considered before the transplant occurs.

REFERENCE VALUES

IgM: Negative

IgG: Negative; titer 1:4

How the test is done

Venipuncture is performed to obtain a sample of the blood.

If the pregnant female has varicella infection, amniotic fluid analysis from amniocentesis or blood from a percutaneous umbilical blood sampling may be obtained to identify infection in the fetus.

Significance of test results

Positive values

Past or present varicella-zoster infection

Immunity to future varicella infection

Interfering factors

• Infection with another type of herpesvirus

NURSING CARE

Nursing actions are similar to those used in venipuncture procedures (see Chapter 2), with the following additional measures.

Pretest

• Inform the adult patient that a positive IgG antibody titer indicates immunity from future chickenpox infection.

Posttest

• If the newborn has a recent exposure to the varicella-zoster virus, the nurse maintains the infant in isolation in the newborn nursery. To determine the presence of perinatal infection, the physician may have the infant’s blood tested for IgM antibodies. To reduce the severity of the infection in this newborn, the nurse prepares to administer varicella immunoglobulin to the baby, as prescribed by the physician.

Health promotion

To prevent chickenpox, the recommended time for infant child vaccination with measles, mumps, rubella, varicella-zoster (MMRV) is between 12 and 15 months old. If the varicella vaccination is given separately, it is given no earlier than 12 months old. A second dose is given between 4 and 6 years old.

The vaccine is also recommended for people who are frequently in settings where infection rates are higher, including hospitals, day care centers, schools, prisons, military settings, and colleges. The nonpregnant female also should be vaccinated to prevent severe illness during a future pregnancy and avoid potential risk to the fetus.

Health teaching

The nurse can teach individuals and community groups about the importance of early vaccination of their infants and young children, encouraging them to have their children vaccinated to prevent this infection.

Vasopressin

Also called: Antidiuretic Hormone (ADH), Arginine-Vasopressin (AVP)

Specimen or type of test:

Plasma

Purpose of the test

A serum antidiuretic hormone (ADH) determination is obtained to diagnose diabetes insipidus and syndrome of inappropriate antidiuretic hormone (SIADH).

Basics the nurse needs to know

Vasopressin (ADH) is produced by the hypothalamus and stored in the posterior pituitary gland. Its major function in the body is to act on the cells in the collecting ducts of the kidney, making them more permeable to water. The result is an increased reabsorption of water. This action is independent of electrolyte levels, and electrolytes are not reabsorbed with the water. The purpose of this action is to maintain normal plasma osmolality. ADH also has a vasopressor effect. It causes arteriole smooth muscles to constrict, thus elevating the blood pressure.

ADH is released from the posterior pituitary gland in response to several stimuli. The major stimulus is an increase in plasma osmolality. Whenever the osmoreceptors in the anterior hypothalamus sense even minor changes in plasma osmolality, neural stimulation of the pituitary gland will result in an increased secretion of ADH, which will result in an increased reabsorption of water at the renal collecting ducts. With the increase in water in the extracellular fluid, blood tonicity will decrease. Because the increase in water results in decreased blood osmolality, the osmoreceptors will cease the neural stimulation necessary for ADH secretion (Figure 104).

Figure 104. Vasopressin (ADH) regulation. ADH is secreted by the posterior pituitary gland primarily in response to an increase in plasma osmolality.

Another stimulant for ADH release is the extracellular fluid volume. A drop in blood volume is sensed by stretcher receptors primarily in the vena cava and right atrium. By way of the brainstem, these receptors tell the hypothalamus to stimulate the release of ADH from the posterior pituitary gland. The resultant increase in fluid volume from water retention results in a decrease in stretcher receptor stimulation. In addition, as arterial blood pressure drops, pressor receptors found in the aorta and coronary sinuses will stimulate the release of ADH to increase extracellular fluid volume and thus the patient’s blood pressure.

ADH secretion may be increased by drugs (e.g., nicotine, opiates, barbiturates, chlorpropamide) and severe pain, stress, and hyperthermia. Decreased sensitivity of the kidneys to ADH occurs with the intake of lithium carbonate and demeclocycline.

REFERENCE VALUES

If serum osmolality is >290 mOsm/kg: 2-12 pg/mL or SI: 1.85-11.1 pmol/L

If serum osmolality is <290 mOsm/kg: <2 pg/mL or SI: <1.85 pmol/L

How the test is done

Venipuncture is performed and specimen sent to the lab immediately.

Significance of test results

Elevated values

Syndrome of inappropriate antidiuretic hormone

Guillain-Barre syndrome

Tuberculosis

Decreased values

Diabetes insipidus

Nephrotic syndrome

Psychogenic polydipsia

Interfering factors

• Noncompliance with diet, activity, and medication restrictions

• Pain

• Stress

• Mechanical ventilation

• Alcohol

• Medications such as anesthetics, antipsychotics, carbamazepine, chlorothiazide, cyclophosphamide, estrogen, lithium, oxytocin, phenytoin, and vincristine

NURSING CARE

Nursing actions related to venipuncture are presented in Chapter 2, with the following additional measures.

Pretest

•   Patient teaching.

The nurse instructs the patient not to eat or drink for 12 hours before the test.

•   Patient teaching.

The nurse also instructs the patient to avoid substances that increase ADH secretion, such as nicotine, alcohol, caffeine, and diuretics. Instruct the patient to limit physical activity for 12 hours before the test. The patient should lie down and rest for 30 minutes before the blood is drawn.

• Obtain a medication history to determine if any interfering drugs are being taken. In the pretest period, the nurse checks with the physician to determine if these drugs are to be withheld or continued.

• Assess the patient for pain and stress, which may interfere with results.

Posttest

• Send specimen to the laboratory immediately.

• Instruct the patient to resume normal activity and diet.

• The nurse administers prescribed medications that were withheld for the test.

Vectorcardiogram

Also called: VCG

Specimen or type of test:

Electrophysiology

Purpose of the test

A vectorcardiogram is used to assess ischemia, conduction defects, and chamber enlargement (hypertrophy or dilation).

Basics the nurse needs to know

A vectorcardiogram is a graphic recording of electric forces of the heart. It is a noninvasive procedure that graphically records the direction and magnitude of the heart’s electric forces by means of a continuous series of vector loops. Three planes of the heart are recorded (frontal, sagittal, and horizontal).

REFERENCE VALUES

Normal cardiac axis

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