Washing CytologySee Bronchial Washing—Specimen.

Water Deprivation Test for Vasopressin DeficiencySee Concentration Test—Urine.

Water Loading Test—DiagnosticNorm. ≥500-mL urine output over 4 hours after water ingestion.Urine osmolality < serum osmolality or <180 mOsm/kg by 5 hours after water ingestion.

Usage. Diagnosis of syndrome of inap-propriate antidiuretic hormone secretion (SIADHS).

Description. The water loading test involves administering a large quantity of

Weil-Felix Agglutinins—Blood 1187

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Procedure1. Draw a 4-mL blood sample for the base-

line serum osmolality. Obtain a 20-mL random urine sample in a clean plastic container for baseline urine osmolality.

2. Have the client drink 1 L of water, or 20 mL/kg of body weight, over 15-20 minutes, or instill it through a nasogastric tube.

3. Document the quantity of urine output, starting with the time of water ingestion and ending 5 hours later.

4. Obtain samples for serum and urine osmolality as in step 1 every hour for 5 hours. Label each tube sequentially, and write the collection time on the label.

Postprocedure Care1. Refrigerate the serum samples if they are

not tested within 4 hours.2. Refrigerate all urine samples until they

are tested.

Client and Family Teaching1. The client will be asked to drink or have

instilled at least 1 L of water within 20 minutes.

Factors That Affect Results1. Diuretics administered within 12 hours

before the test invalidate the results.

Other Data1. Terlipressin increases water excretion in

nonazotemic cirrhotic patients without hyponatremia.

water and then comparing the osmolality of timed urine and serum collections. In a normal client, increased fluid intake increases urine output and decreases urine osmolality. In clients with SIADHS, however, excess secretion of antidiuretic hormone causes a lower-than-normal urine output in response to the water loading and a urine osmolality that does not decrease below serum osmolality.

Professional ConsiderationsConsent form NOT required.

RisksFluid overload, congestive heart failure. Complications of nasogastric tube insertion include bleeding, dysrhythmias, esophageal perforation, laryngospasm, and decreased mean pO2.

Contraindications and PrecautionsPerform with extreme caution in clients with a history of congestive heart failure.

Preparation1. The baseline serum sodium level should

be at least 125 mEq/L before this test is started.

2. Withhold diuretics for 12 hours before the test.

3. Tube: Six red topped, red/gray topped, or gold topped.

4. Also obtain six clean plastic specimen containers.

5. Insert a nasogastric tube if the client will be unable to drink 1 L of water over a short period of time.

Weber TestSee Tuning Fork Test, of Weber, Rinne, and Schwabach Tests—Diagnostic.

Weil-Felix Agglutinins—BloodNorm. A less than fourfold rise in titer between acute and convalescent samples; or titer <1 : 160.

Usage. Helps in the diagnosis of rickettsial infections.

Description. A test performed for the purpose of detecting and differentiating rickettsial antibodies in the serum. Rickett-sial organisms cause Rocky Mountain

spotted fever, Q fever, Brill-Zinsser disease, epidemic typhus, murine typhus, scrub typhus, and rickettsialpox. Three Proteus antigens are known to cross-react in specific relationships with rickettsial antibodies. The test is performed by mixture of serial dilu-tions of test serum with suspensions of Proteus strains OX-2, OX-19, and OX-K and observation for agglutination. A single titer >1 : 320 or a fourfold rise in titer between

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1188 Westergren Sedimentation Rate

acute and convalescent samples is consid-ered diagnostic.

Professional ConsiderationsConsent form NOT required.

Preparation1. Tube: Red topped, red/gray topped, or

gold topped.2. Specimens MAY be drawn during

hemodialysis.

Procedure1. Draw a 10-mL blood sample and label it

as the “acute sample.” Repeat the test every 3-5 days. Draw a final sample in 10-14 days, and label it as the “convales-cent sample.”

Postprocedure Care1. None.

Client and Family Teaching1. Return for serial sampling as prescribed

and then in 10-14 days for final follow-up testing.

Factors That Affect Results1. Hemolysis invalidates the results.2. Immunosuppressed clients may be

infected but have low or negative titers.3. Antibiotic therapy causes low initial titers.

Other Data1. Because the test is based on a known

cross-reaction, caution must be used in interpreting the results. Although dif-ferentiation between Rocky Mountain spotted fever and typhus fever is not possible with this test, interpretation of results can rule out certain rickettsial infections.

2. See also Febrile agglutinins—Serum.

Westergren Sedimentation RateSee Sedimentation Rate, Erythrocyte—Blood.

Western BlotSee Acquired Immune Deficiency Syndrome Evaluation Battery—Diagnostic.

Western Equine Encephalitis Virus Serology—SerumNorm. Negative. A less than fourfold rise in titer between acute and convalescent samples; HI (hemagglutination inhibition) antibody titer <1 : 10; no IgM antibody detected; IFA IgG <1 : 16 and IgM <1 : 16.

Positive. Aseptic meningitis and meningoencephalitis.

Description. Western equine encephalitis is caused by a group A arbovirus (arthropod-borne virus), specifically, togavirus, which results in inflammation of parts of the brain, meninges, and spinal cord in horses and humans. Occurrence is primarily in the Western Hemisphere and in summer to early fall. Mode of transmission to humans is from small birds and mammals through the bite of an infected mosquito. Symptoms are short in duration and may range from mild to fatal (10%) encephalitis symptoms (stiff neck, lethargy, sore throat, vomiting, stupor,

coma, paralysis in children). Identification of the virus is performed through viral neu-tralization, complement fixation, hemagglu-tinin inhibition, fluorescent antibody, and agar gel precipitation. A positive IgG or IgM result indicates current or recent infection.

Professional ConsiderationsConsent form NOT required.

Preparation1. Tube: Red topped, red/gray topped, or

gold topped.

Procedure1. Draw a 7-mL blood sample as soon as

possible after symptoms appear, and label it as the “acute sample.” Repeat the test in 14 days, and label it as the “convalescent sample.”

Postprocedure Care1. None.

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Wound Culture 1189

Client and Family Teaching1. The mode of transmission is by a mos-

quito bite. Wear insect-repellant spray or lotion on skin when outdoors.

2. Return in 2 weeks for follow-up testing.

Factors That Affect Results1. Cross-reactions may occur with eastern

equine encephalitis virus, another group A togavirus.

2. Disease cannot be excluded if sample is drawn within 2 weeks of symptom onset.

Other Data1. Testing may also be performed on cere-

brospinal fluid.2. Western equine encephalitis is not trans-

mitted client to client.

WFDC2See Human Epididymis Protein 4—Blood.

White Blood Cell Count DifferentialSee Differential Leukocyte Count—Peripheral Blood.

White Blood CountSee Differential Leukocyte Count—Peripheral Blood.

Whole-Body ScanSee Bone Scan—Diagnostic.

Wintrobe Sedimentation RateSee Sedimentation Rate, Erythrocyte—Blood.

Wound, FungusSee Biopsy, Site-Specific—Specimen; Body Fluid, Fungus—Culture.

Wound, MycobacteriaSee Biopsy, Site-Specific—Specimen; Body Fluid, Mycobacteria—Culture.

Wound CultureSee Culture, Routine—Specimen.