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Immunodiagnostic Studies Overview of Immunodiagnostic Studies / 550 • Types of Tests / 551 • Collection of Serum for Immunologic Tests / 551 • Interpreting Results of Immunologic Tests / 551 • Serologic Versus Microbiologic Methods / 554 ● BACTERIAL TESTS / 554 Syphilis Detection Tests / 554 Lyme Disease Tests / 557 Legionnaires’ Disease Antibody Test / 558 Chlamydia Antibody IgG Test / 559 Streptococcal Antibody Tests: Antistreptolysin O Titer (ASO), Streptozyme, Antideoxyribonuclease-B Titer (Anti-DNase-B, ADNase-B) (ADB, Streptodornase) / 560 Helicobacter pylori (HPY) IgG Antibody Serum, Stool, and Breath (PY) Test / 561 ● VIRAL TESTS / 563 Epstein-Barr Virus (EBV) Antibody Tests: Infectious Mononucleosis (IM) Slide (Screening) Test, Heterophile Antibody Titer, Epstein-Barr Antibodies to Viral Capsid Antigen and Nuclear Antigen / 563 Hepatitis Tests: Hepatitis A (HAV), Hepatitis B (HBV), Hepatitis C (HCV), Hepatitis D (HDV), Hepatitis E (HEV), Hepatitis G (HGV) / 564 Human Immunodeficiency Virus (HIV-1/2) Antibody Tests, HIV Group O, Antibody to Human Immunodeficiency Virus (HIV-1/2); Acquired Immunodeficiency Syndrome (AIDS) Tests / 572 ● VIRAL ANTIBODY TESTS TO ASSESS IMMUNE STATUS / 576 Rubella Antibody Tests / 576 Measles (Rubeola) Antibody Tests / 577 Mumps Antibody Tests / 578 8 Varicella-Zoster (Chickenpox) Antibody Test / 580 Cytomegalovirus (CMV) Antibody Test / 581 Herpes Simplex Virus (HSV) Antibodies (HSV-1 and HSV-2 Tests) / 582 Human T-Cell Lymphotropic Virus (HTLV-I/II) Antibody Test / 582 Parvovirus B-19 Antibody Test / 583 Rabies Antibody Tests / 584 ● FUNGAL TESTS / 585 Fungal Antibody Tests: Histoplasmosis, Blastomycosis, Coccidioidomycosis / 585 Candida Antibody Test / 586 Aspergillus Antibody Test / 587 Cryptococcus Antibody Test / 587 ● PARASITIC TESTS / 588 Toxoplasmosis (TPM) Antibody Tests / 588 Amebiasis (Entamoeba histolytica) Antibody Test / 589 TORCH Test / 590 ● IMMUNOLOGIC TESTS FOR IMMUNE DYSFUNCTION AND RELATED DISORDERS OF THE IMMUNE SYSTEM / 591 Quantitative Immunoglobulins: IgA, IgG, IgM / 591 Protein Electrophoresis (PEP), Serum and Urine / 593 Immunofixation Electrophoresis (IFE), Serum and Urine / 596 Cold Agglutinin / 597 Cryoglobulin Test / 599 Total Hemolytic Complement (CH50) / 600 C3 Complement Component / 602 C4 Complement Component / 603 Cⴕ1 Esterase Inhibitor (Cⴕ1 INH) / 603 ● TESTS FOR AUTOIMMUNITY AND SYSTEMIC RHEUMATIC DISEASE (SRD) / 604 Antinuclear Antibody (ANA) Test / 604 Anticentromere Antibody Test / 605 549 Fischbach_Ch08_printer_file.indd 549 11/4/13 10:27 PM 550 CHAPTER 8 ● Overview of Immunodiagnostic Studies Anti-dsDNA Antibody Test, IgG / 606 Rheumatoid Factor (Rheumatoid Arthritis [RA] Factor) Test / 606 Antibodies to Extractable Nuclear Antigens (ENAs): Anti-Ribonucleoprotein (RNP); Anti-Smith (Sm); Anti-Sjögren’s Syndrome (SSA, SSB); Anti-Scleroderma (Scl-70); Anti-Jo-1 (Jo-1) / 607 Cardiolipin Antibodies, IgA, IgG, IgM / 609 Autoimmune Thyroiditis, Thyroid Antibody Tests: Thyroglobulin Antibody, Thyroid Microsomal Antibody, Thyroperoxidase Antibody / 609 ● AUTOIMMUNE LIVER DISEASE TESTS / 611 Anti–Smooth Muscle Antibody (ASMA) Test / 611 Antimitochondrial Antibody (AMA) Test / 612 Anti–Liver/Kidney Microsome Type 1 Antibody (LKM) Test / 613 Antiparietal Cell Antibody (APCA) Test / 613 Antiglomerular Basement Membrane (AGBM) Antibody Test / 614 Acetylcholine Receptor (AChR) Binding Antibody Test / 615 Anti-Insulin Antibody Test / 616 Gliadin Antibodies, IgA and IgG / 616 Antineutrophil Cytoplasmic Antibodies (ANCAs) / 617 ● SPERM ANTIBODIES / 618 Antisperm Antibody Test / 618 ● ALLERGY TESTING / 620 IgE Antibody, Single Allergen / 620 Latex Allergy Testing (Latex-Specific IgE) / 621 ● PROTEIN CHEMISTRY TESTING/SERUM PROTEINS: ACUTE-PHASE PROTEINS AND CYTOKINES / 622 Ceruloplasmin / 622 ␣1-Antitrypsin / 623 C-Reactive Protein (CRP) and High-Sensitivity C-Reactive Protein (hs-CRP) / 624 Prion Proteins / 625 Cytokines / 626 Tumor Markers / 628 ● BLOOD BANKING OR IMMUNOHEMATOLOGY TESTS / 645 Donated Blood Testing and Blood Processing / 645 Blood Groups (ABO Groups) / 648 Rh Typing / 650 Rh Antibody Titer Test / 652 Rosette Test, Fetal Red Cells (Fetal-Maternal Bleed) / 653 Kleihauer-Betke Test (Fetal Hemoglobin Stain) / 653 Crossmatch (Compatibility Test) / 655 Coombs’ Antiglobulin Test / 659 ● TYPES OF TRANSFUSION REACTIONS / 660 • Acute Hemolytic Transfusion Reaction (HTR) / 660 • Bacterial Contamination / 660 • Cutaneous Hypersensitivity Reactions / 660 • Noncardiogenic Pulmonary Reactions (NPR) / 660 • Febrile Nonhemolytic (FNH) Reactions / 661 • Anaphylactic Reactions / 661 • Circulatory Overload / 661 Leukoagglutinin Test / 661 Platelet Antibody Detection Test / 662 Human Leukocyte Antigen (HLA) Test / 663 ● ORGAN AND TISSUE TRANSPLANT TESTING / 665 OVERVIEW OF IMMUNODIAGNOSTIC STUDIES Immunodiagnostic or serodiagnostic testing studies antigen-antibody reactions for diagnosis of infectious disease, autoimmune disorders, immune allergies, and neoplastic disease. These modalities also test for blood groups and types, tissue and graft transplant matching, and cellular immunology. Blood serum is tested for antibodies against particular antigens—hence the term blood serology testing. Antigens are substances that stimulate and subsequently react with the products of an immune response. They may be enzymes, toxins, microorganisms (e.g., bacterial, viral, parasitic, fungal), tumors, or autoimmune factors. Antibodies are proteins produced by the body’s immune system in response to an antigen or antigens. The antigen-antibody response is the body’s natural defense against invading organisms. Red blood cell groups contain almost 400 antigens. Immune reactions to these antigens result in a wide variety of clinical disorders, which can be tested (e.g., Coombs’ test). Fischbach_Ch08_printer_file.indd 550 11/4/13 10:27 PM ● Overview of Immunodiagnostic Studies 551 Pathologically, autoimmune disorders are produced by autoantibodies—that is, antibodies against self. Examples include systemic rheumatic diseases, such as rheumatoid arthritis and lupus erythematosus. Immunodeficiency diseases exhibit a lack of one or more basic components of the immune system, which includes B lymphocytes, T lymphocytes, phagocytic cells, and the complement system. These diseases are classified as primary (e.g., congenital, DiGeorge syndrome) and secondary (e.g., acquired immunodeficiency syndrome [AIDS]). Hypersensitivity reactions are documented using immediate hypersensitivity tests and are defined as abnormally increased immune responses to some allergens (e.g., allergic reaction to bee stings or pollens). Delayed hypersensitivity skin tests are commonly used to evaluate cellmediated immunity. Histocompatibility antigens (transplantation antigens) and tests for human leukocyte antigen (HLA) are important diagnostic tools to detect and prevent immune rejection in transplantation. Types of Tests Many methods of varying sophistication are used for immunodiagnostic studies (Table 8.1). Collection of Serum for Immunologic Tests Specific antibodies can be detected in serum and other body fluids (e.g., synovial fluid, CSF). 1. Procure samples. For diagnosis of infectious disease, a blood sample (serum preferred) using a 7-mL red-topped tube should be obtained at illness onset (acute phase), and the other sample should be drawn 3 to 4 weeks later (convalescent phase). In general, serologic test usefulness depends on a titer increase in the time interval between the acute and the convalescent phase. For some serologic tests, one serum sample may be adequate if the antibody presence indicates an abnormal condition or the antibody titer is unusually high. See Appendix A for standard precautions. 2. Perform the serologic test before doing skin testing. Skin testing often induces antibody production and could interfere with serologic test results. 3. Label the sample properly and submit requested information. Place specimen in biohazard bag. Send samples to the laboratory promptly. Hemolyzed samples cannot yield accurate results. Hemoglobin in the serum sample can interfere with complement-fixing antibody values. Interpreting Results of Immunologic Tests The following factors affect test results: 1. History of previous infection by the same organism 2. Previous vaccination (determine time frame) 3. Anamnestic reactions caused by heterologous antigens: An anamnestic reaction is the appearance of antibodies in the blood after administration of an antigen to which the patient has previously developed a primary immune response. 4. Cross-reactivity: Antibodies produced by one species of an organism can react with an entirely different species (e.g., Tularemia antibodies may agglutinate Brucella and vice versa, rickettsial infections may produce antibodies reactive with Proteus OX19). 5. Presence of other serious illness states (e.g., lack of immunologic response in agammaglobulinemia, cancer treatment with immunosuppressant drugs) 6. Seroconversion: the detection of specific antibody in the serum of an individual when this antibody was previously undetectable Fischbach_Ch08_printer_file.indd 551 11/4/13 10:27 PM 552 CHAPTER 8 ● Overview of Immunodiagnostic Studies TABLE 8.1 Some Tests That Determine Antigen-Antibody Reactions Name of Test Observable Reaction Visible Change Tests for Agglutination, hemagglutination (HA), immune hemagglutination assay (IHA) Particulate antigen reacts with corresponding antibody; antigen may be in form of RBCs (hemagglutination, latex, or charcoal coated with antigen). Clumping Treponemal, heterophile, and cold agglutinin antibodies Precipitation (e.g., immunodiffusion [ID], counterimmunoelectrophoresis [CIE]) Soluble antigen reacts with corresponding antibody by ID or count. Precipitates Fungal antibodies, food poisoning Complement fixation (CF) Competition between two antigen-antibody systems (test and indicator systems) Complement activation, hemolysis Viral antibodies Immunofluorescence (e.g., indirect fluorescent antibody [IFA]) Fluorescenttagged antibody reacts with antigen-antibody complex in the presence of ultraviolet light. Visible microscopic fluorescence Antinuclear antibodies (ANAs); antimitochondrial antibodies (AMAs) Enzyme immunoassay (EIA) Enzymes are used to label induced antigen-antibody reactions. Chromogenic fluorescent or luminescent change in substrate Hepatitis and human immunodeficiency virus (HIV) (screening) Enzyme-linked immunosorbent assay (ELISA) Indirect EIA for quantification of an antigen or antibody enzyme and substrate Color change indicates enzyme substrate reaction. Lyme disease, Epstein-Barr virus, extractable nuclear antibodies (connective tissue/ systemic rheumatic disease) Immunoblot (e.g., Western blot [WB]) Electrophoresis separation of antigen subspecies Detection of antibodies of specific mobility Confirms HIV-1 table continues on pg. 553 > Fischbach_Ch08_printer_file.indd 552 11/4/13 10:27 PM ● Overview of Immunodiagnostic Studies 553 TABLE 8.1, continued Observable Reaction Visible Change Tests for Polymerase chain reaction (PCR) Amplifies low levels of specific DNA sequences; each cycle doubles the amount of specific DNA sequence. Exponential accumulation of DNA fragment being amplified; defects in DNA appear as mutations. Slightest trace of infection can be detected; more accurate than traditional tests for chlamydia; genetic disorders Rate nephelometry Measures either antigen or antibody in solution through the scattering of a light beam; antibody reagent used to detect antigen IgA, IgG, IgM; concurrent controls are run to establish amount of background scatter in reagents and test samples. Light scatter proportionately increases as numbered size of immune complexes increases. Quantitative immunoglobulins IgA, IgM, C-reactive protein, antistreptolysin O recorded in mg/dL or IU/mL Flow cytometry Blood cell types are identified with monoclonal antibodies (mABs) specific for cell markers by means of a flow cytometer with an argon laser beam; as the cells pass the beam, they scatter the light; light energy is converted into electrical energy cells and stained with green (fluorescence) or orange (phytoerythrin). Light scatter identifies cell size and granularity of lymphocytes, monocytes, and granulocytes; color fluorochromes tagged to monoclonal antibodies bind to specific surface antigens for simultaneous detection of lymphocyte subsets. Lymphocyte immunophenocytology differentiates B cells from T cells and T-helper cells from T-suppressor cells. Restriction fragment length polymorphism (RFLP) DNA-based typing technique cDNA probes Uses cDNA probes directed against ribosomal RNA Name of Test Fischbach_Ch08_printer_file.indd 553 Epidemiology of nosocomial and communityacquired infections Amplifies nucleic acid to identify presence of bacterial or viral load Infectious disease such as tuberculosis, hepatitis C virus, and HIV 11/4/13 10:27 PM 554 CHAPTER 8 ● Syphilis Detection Tests Serologic Versus Microbiologic Methods Serologic testing for microbial immunology evaluates the presence of antibodies produced by antigens of bacteria, viruses, fungi, and parasites. The best means of establishing infectious disease etiology is by isolation and confirmation of the involved pathogen. Serologic methods can assist or confirm microbiologic analysis when the patient is tested late in the disease course, antimicrobial therapy has suppressed organism growth, or culture methods cannot verify a causative agent. BACTERIAL TESTS ● Syphilis Detection Tests Syphilis is a venereal disease caused by Treponema pallidum, a spirochete with closely wound coils approximately 8 to 15 ␮m long. Untreated, the disease progresses through three stages that can extend over many years. Antibodies to syphilis begin to appear in the blood 4 to 6 weeks after infection (Table 8.2). Nontreponemal tests determine the presence of reagin, which is a nontreponemal autoantibody directed against cardiolipin antigens. These tests include the rapid plasma reagin (RPR) and Venereal Disease Research Laboratory (VDRL) tests. The U.S. Centers for Disease Control and Prevention (CDC) recommend these tests for syphilis screening; however, they may show negative results in some cases of late syphilis. Biologic false-positive results can also occur (Table 8.3). Conversely, treponemal (i.e., specific) tests detect antibodies to T. pallidum. These tests include the passive particle agglutination T. pallidum test (TP-PA) and the fluorescent treponemal antibody absorption test (FTA-ABS). These tests confirm syphilis when a positive nontreponemal test result is obtained. Because these tests are more complex, they are not used for screening. Certain states require automatic confirmation for all reactive screening tests by using a treponemal test such as the TP-PA or FTA-ABS. Reference Values Normal Nonreactive, negative for syphilis TABLE 8.2 Sensitivity of Commonly Used Serologic Tests for Syphilis Stage Test Primary Secondary Late (%) (%) (%) Nontreponemal (Reagin) Tests Venereal Disease Research Laboratory test (VDRL) Rapid plasma reagin card test (RPR); automated reagin test (ART) 70 80 99 99 1* 0 Specific Treponemal Tests Fluorescent treponemal antibody absorption test (FTA-ABS) Treponema pallidum particle agglutination (TP-PA) 85 65 100 100 98 95 (This new procedure has sensitivity similar to MHA-TP.) *Treated late syphilis. Modified from Tramont EC: Treponema pallidum. In Mandell GI, Douglas RE, Bennett JE (eds): Principles and Practice of Infectious Diseases. New York, John Wiley & Sons, 1985, p. 1329. Also product insert Serodia TP-PA, Fujirebio, Inc., Tokyo, Japan, 2000. Fischbach_Ch08_printer_file.indd 554 11/4/13 10:27 PM ● Syphilis Detection Tests 555 TABLE 8.3 Nonsyphilitic Conditions Giving Biologic False-Positive Results (BFPs) Using VDRL and RPR Tests Disease Malaria Leprosy Relapsing fever Active immunization in children Infectious mononucleosis Lupus erythematosus Lymphogranuloma venereum Pneumonia, atypical Rat-bite fever Typhus fever Vaccinia Infectious hepatitis Leptospirosis (Weil’s disease) Periarteritis nodosa Trypanosomiasis Chancroid Chickenpox Measles Rheumatoid arthritis Rheumatic fever Scarlet fever Subacute bacterial endocarditis Pneumonia, pneumococcal Tuberculosis, advanced pulmonary Blood loss, repeated Common cold Pregnancy NOT E Approximate Percentage BFPs 100 60 30 20 20 20 20 20 20 20 20 10 10 10 10 5 5 5 5–7 5–6 5 5 3–5 3–5 ? (low) ? (low) ? (low) A reactive RPR or VDRL test should be confirmed with an FTA-ABS or TP-PA. Sensitivity of FTA-ABS Primary syphilis: 84% Secondary syphilis: 100% Latent syphilis: 100% Late syphilis: 96% Sensitivity of TP-PA Primary syphilis: 86% Secondary syphilis: 100% Latent syphilis: 100% Procedure 1. Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Fasting is usually not required. 2. Place specimen in a biohazard bag for transport to the laboratory. Fischbach_Ch08_printer_file.indd 555 11/4/13 10:27 PM 556 CHAPTER 8 ● Syphilis Detection Tests PROCEDURAL ALERT If the RPR test is used, the following need to be observed: 1. Excess chyle released into the blood during digestion interferes with test results; therefore, the patient should fast for 8 hours. 2. Alcohol decreases reaction intensity in tests that detect reagin; therefore, alcohol ingestion should be avoided for at least 24 hours before blood is drawn. Clinical Implications 1. Diagnosis of syphilis requires correlation of patient history, physical findings, and results of syphilis antibody tests. T. pallidum is diagnosed when both the screening and the confirmatory tests are reactive. 2. Treatment of syphilis may alter both the clinical course and the serologic pattern of the disease. Treatment related to tests that measure reagin (RPR and VDRL) includes the following measures: a. If the patient is treated at the seronegative primary stage (e.g., after the appearance of the syphilitic chancre but before the appearance of reaction or reagin), the VDRL remains nonreactive. b. If the patient is treated in the seropositive primary stage (e.g., after the appearance of a reaction), the VDRL usually becomes nonreactive within 6 months of treatment. c. If the patient is treated during the secondary stage, the VDRL usually becomes nonreactive within 12 to 18 months. d. If the patient is treated ⬎10 years after the disease onset, the VDRL usually remains unchanged. 3. A negative serologic test may indicate one of the following circumstances: a. The patient does not have syphilis. b. The infection is too recent for antibodies to be produced. Repeat tests should be performed at 1-week, 1-month, and 3-month intervals to establish the presence or absence of disease. c. The syphilis is in a latent or inactive phase. d. The patient has a faulty immunodefense mechanism. e. Laboratory techniques were faulty. False-Positive and False-Negative Reactions A positive reaction is not conclusive for syphilis. Several conditions produce biologic false-positive results for syphilis. Biologic false-positive reactions are by no means “false.” They may reveal the presence of other serious diseases. It is theorized that reagin (reaction) is an antibody against tissue lipids. Lipids are presumed to be liberated from body tissue in the normal course of activity. These liberated lipids may then induce antibody formation. Nontreponemal biologic false-positive reactions can occur in the presence of drug abuse, lupus erythematosus, mononucleosis, malaria, leprosy, viral pneumonia, recent immunization, or, on rare occasions, pregnancy. False-negative reactions may occur early in the disease course or during inactive or later stages of disease. Interfering Factors 1. Hemolysis can cause false-positive results. 2. Hepatitis can result in a false-positive test. 3. Testing too soon after exposure can result in a false-negative test. Interventions Pretest Patient Care 1. Explain test purpose and procedure. Assess for interfering factors. Instruct the patient to abstain from alcohol for at least 24 hours before the blood sample is drawn. 2. Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care. Fischbach_Ch08_printer_file.indd 556 11/4/13 10:27 PM ● Lyme Disease Tests 557 Posttest Patient Care 1. Interpret test results and counsel appropriately. Explain biologic false-positive or false-negative reactions. Advise that repeat testing may be necessary. 2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care. CLINICAL ALERT 1. Sexual partners of patients with syphilis should be evaluated for the disease. 2. After treatment, patients with early-stage syphilis should be tested at 3-month intervals for 1 year to monitor for declining reactivity. ● Lyme Disease Tests Lyme disease is a multisystem disorder caused by the spirochete Borrelia burgdorferi. It is transmitted by the bite of tiny deer ticks, which reside on deer and other wild animals. Lyme disease is present worldwide, but certain geographic areas show higher incidences. Transmission to humans is highest during the spring, summer, and early fall months. The tick bite usually produces a characteristic rash, termed erythema chronicum migrans. If untreated, sequelae lead to serious joint, cardiac, and central nervous system (CNS) symptoms. Serologic testing for antibodies to Lyme disease includes enzyme-linked immunosorbent assay (ELISA) and Western blot analysis. Antibody formation takes place in the following manner: Immunoglobulin M (IgM) is detected 3 to 4 weeks after Lyme disease onset, peaks at 6 to 8 weeks after onset, and then gradually disappears. IgG is detected 2 to 3 months after infection and may remain elevated for years. Current CDC recommendations for the serologic diagnosis of Lyme disease are to screen with a polyvalent ELISA (IgG and IgM) and to perform supplemental testing (Western blot) on all equivocal and positive ELISA results. Western blot assays for antibodies to B. burgdorferi are supplemental rather than confirmatory because their specificity is less than optimal, particularly for detecting IgM. Two-step positive results provide supportive evidence of exposure to B. burgdorferi, which could support a clinical diagnosis of Lyme disease but should not be used as a criterion for diagnosis. Reference Values Normal Negative for both IgG and IgM Lyme antibodies by ELISA and Western blot Procedure 1. Collect a 7-mL blood serum sample in a red-topped tube. CSF may also be used for the test. 2. Observe standard precautions. 3. Place specimen in a biohazard bag. Clinical Implications 1. Ten proteins are useful in the serodiagnosis of Lyme disease. Positive blots are: a. IgM: two of three of the following bands: 21/25, 39, and 41 b. IgG: five of the following bands: 18, 21/25, 28, 30, 39, 41, 45, 58, 66, and 93 2. Serologic tests lack the degree of sensitivity, specificity, and standardization necessary for diagnosis in the absence of clinical history. The antigen detection assay for bacterial proteins is of limited value in early stages of disease. 3. In patients presenting with a clinical picture of Lyme disease, negative serologic tests are inconclusive during the first month of infection. Fischbach_Ch08_printer_file.indd 557 11/4/13 10:27 PM 558 CHAPTER 8 ● Legionnaires’ Disease Antibody Test 4. Repeat paired testing should be performed if borderline values are reported. 5. The CDC states that the best clinical marker for Lyme disease is the initial skin lesion erythema migrans (EM), which occurs in 60% to 80% of patients. 6. CDC laboratory criteria for the diagnosis of Lyme disease include the following factors: a. Isolation of B. burgdorferi from a clinical specimen b. IgM and IgG antibodies in blood or CSF c. Paired acute and convalescent blood samples showing significant antibody response to B. burgdorferi Interfering Factors 1. False-positive results may occur with high levels of rheumatoid factors or in the presence of other spirochete infections, such as syphilis (cross-reactivity). 2. Asymptomatic individuals who spend time in endemic areas may have already produced antibodies to B. burgdorferi. Interventions Pretest Patient Care 1. Assess patient’s clinical history, exposure risk, and knowledge regarding the test. Explain test purpose and procedure as well as possible follow-up testing. 2. Follow guidelines in Chapter 1 regarding safe, effective, informed pretest care. Posttest Patient Care 1. Interpret test outcomes for a positive test. Advise the patient that follow-up testing may be required to monitor response to antibiotic therapy. 2. Unlike other diseases, people do not develop resistance to Lyme disease after infection and may continue to be at high risk, especially if they live, work, or recreate in areas where Lyme disease is present. 3. If Lyme disease has been ruled out, further testing may include Babesia microti, a parasite transmitted to humans by a tick bite. Symptoms include loss of appetite, fever, sweats, muscle pain, nausea, vomiting, and headaches. 4. Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care. ● Legionnaires’ Disease Antibody Test Legionnaires’ disease is a respiratory condition caused by Legionella pneumophila. It is best diagnosed by organism culture; however, the organism is difficult to grow. Detection of L. pneumophila in respiratory specimens by means of direct fluorescent antibody (DFA) technique is useful for rapid diagnosis but lacks sensitivity when only small numbers of organisms are available. Serologic tests should be used only if specimens for culture are not available or if culture and DFA produce negative results. Reference Values Normal Negative for legionnaires’ disease by indirect fluorescent antibody (IFA) test or ELISA Procedure 1. Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Place specimen in a biohazard bag for transport to the laboratory. 2. Follow-up testing is usually requested 3 to 6 weeks after initial symptom appearance. 3. Alert patient that a urine specimen may be required if antigen testing is indicated. Fischbach_Ch08_printer_file.indd 558 11/4/13 10:27 PM