Medical Terminology: Tests for Infection

1. What are Tests for Infection?
Signs and symptoms of an infection typically indicate that a microorganism has invaded the patient’s body. There has been a tendency for health care providers to prescribe an antibiotic at the first sign of an infection. In doing so, the health care provider assumes that the patient is experiencing a bacterial infection and that the antibiotic will eliminate the bacteria. Typically, if the infection does not improve within 7. to 10. days of antibiotic treatment, the patient will undergo an additional assessment.
Over time, this approach to treating infection has been one of many factors leading to antibiotic-resistant bacteria. The bacteria adapted to common antibiotics, making the antibiotic useless. Today health care providers are encouraged to order tests that identify the microorganism as well as tests to identify the best medication to kill the microorganism. These tests are called culture and sensitivity tests.
A sample of the patient’s blood or infected tissue is sent to the laboratory, where the microorganism is encouraged to replicate in a culture dish. Laboratory specialists then conduct tests to identify the microorganism. Once identified, the microorganism is exposed to medication known to kill it. The laboratory specialist determines the best medication and the minimum dose to administer to the patient that will kill the microorganism. In this way, the proper dose of the right medication can be prescribed, reducing the risk that the microorganism will become resistant to the medication.

2. Antibody Tests
Antibody tests are used to assess the underlying cause of autoimmune hemolytic anemia, blood transfusion reaction, or potential reaction, and screen for the Rh factor.

Understanding Antibody Tests
Antibodies are proteins made by the immune system that bind to bacteria, viruses, and other microorganisms to destroy the microorganism. Antibodies can also bind to red blood cells (RBCs), destroying them as well. Antibody tests determine if antibodies are attacking RBCs. Antibodies are created as a result of:
- Blood Transfusion Reaction: The transfused blood has different antigens on the surface of its RBCs than the patient’s RBCs, which causes the immune system to produce antibodies that attack the transfused RBCs.
- Rhesus Factor Sensitization: The Rh antigen is in the fetus’s blood (Rh positive), but not in the pregnant woman’s blood (Rh negative). During delivery, the fetus’s blood mixes with the mother’s blood, causing the mother’s immune system to create antibodies against the fetus’s RBCs. The mother becomes Rh sensitive. The antibodies can attack the fetus’s RBCs in future pregnancies if the fetus is Rh positive. Women with Rh-negative blood are given the Rh immune globulin (RhoGAM) that typically stops Rh sensitivity.
Rh Antibody Titer: The test is performed in early pregnancy to determine the mother’s blood type and conclude if the mother is Rh negative.
- Autoimmune Hemolytic Anemia: The patient’s immune system creates antibodies against the patient’s RBCs.
Direct Coombs Test: Identifies antibodies attached to the patient’s RBCs. This test is performed:
On a newborn whose mother is Rh negative to determine if the antibodies crossed the placenta into the newborn’s blood
On a patient who received a blood transfusion to determine if there is a transfusion reaction
On a patient to determine if an autoimmune response is occurring
Indirect Coombs Test: This test identifies antibodies that have not but could attach to the patient’s RBCs if the patient’s blood is mixed. This test is performed:
On the blood transfusion recipient or donor before a transfusion to identify if antibodies exist in their blood

3. Blood Cultures
Blood cultures are used to assess:
- Existence of bacteria or fungi in blood
- Endocarditis
- Medication that will kill the microorganism
- Cause of unexplained fever
- Effect of treatment for a microorganism infection

Understanding Blood Cultures
Blood can be infected by bacteria or fungi. A blood culture identifies the bacteria or fungi by allowing the microorganism to grow in a controlled environment and then examining the microorganism under a microscope.
The health care provider typically orders a sensitivity test along with the blood culture. The sensitivity test identifies medication that kills the microorganism.

4. Mononucleosis Tests
Mononucleosis tests are used to assess for infectious mononucleosis.

Understanding Mononucleosis Tests
The Epstein-Barr virus causes mononucleosis. Mononucleosis tests identify antibodies for the Epstein-Barr virus in the blood sample. There are two kinds of mononucleosis tests:
. Monospot: This test identifies heterophil antibodies that form between 2. weeks and 9. weeks after the patient becomes infected.
. EBV Antibody: This test is ordered when the patient shows symptoms of mononucleosis and the monospot test is negative.

5. Helicobacter pylori Tests
Helicobacter pylori tests are used to assess for the presence and treatment of H. pylori.

Understanding Helicobacter pylori Tests
Helicobacter pylori are bacteria that infect the stomach and duodenum, and may result in a peptic ulcer. Many patients have H. pylori, but few develop peptic ulcer disease. Four tests are used to detect H. pylori:
. H. pylori Blood Antibody: This test determines if the blood sample has H. pylori antibodies.
. Urea Breath: This test determines the presence of H. pylori in the stomach.
. H. pylori Stool Antigen: This test determines the presence of H. pylori antigens in feces.
. Stomach Biopsy: This is the endoscopic removal of the lining of the stomach and small intestine, which are examined for the presence of H. pylori.
All tests may produce a false-negative result if the H. pylori count is low and undetectable. The stomach biopsy may produce a false-negative result if the sample was not infected. Blood test for H. pylori antibodies may give a false-positive result since antibodies are present years after the H. pylori infection is resolved.

6. Herpes Tests
Herpes tests are used to assess for the presence of and identification of the type of HSV.

Understanding Herpes Tests
Herpes simplex virus causes painful blister-like sores on the skin and mucous membrane of the mouth, vagina, urethra, rectum, nose, and throat. There are two types of HSV:
- Herpes Simplex Virus Type 1. (HSV-1): Commonly called a fever blister or cold sore that appears on the lips that is spread by direct contact or indirectly through sharing eating utensils.
- Herpes Simplex Virus Type 2. (HSV-2): Commonly called genital herpes, and appears on the penis or vagina and is spread by direct contact.
There are four common tests for HSV:
. Herpes Simplex Virus Antibody Test: This test identifies HSV antibodies in the blood but cannot differentiate between HSV-1. and HSV-2. and can produce a false-negative result since the immune system takes several days to develop sufficient antibodies to be detected by the HSV antibody test.
. Polymerase Chain Reaction (PCR) Test: This test differentiates between HSV-1. and HSV-2. through cell scraping.
. Herpes Virus Antigen Detection Test: This test detects antigens on cells scraped from the HSV sore using a microscope.
. Herpes Viral Culture: This test cultures cells or fluid from an HSV sore to determine if the sore is from HSV-2.
HSV-1. can infect the genitals. HSV-2. can infect the newborn if the mother has HSV-2. HSV-2. can infect the mouth. There is no cure for HSV; however, the HSV can go into remission. Fatigue, stress, or sunlight can cause HSV sores to recur. Varicella zoster is a type of herpes virus that is better known as shingles and chickenpox.

7. Lyme Disease Tests
The Lyme disease tests are used to screen for Lyme disease.

Understanding Lyme Disease Tests
The Borrelia burgdorferi bacteria is carried by ticks and transmitted by a tick bite. The Lyme disease tests detect B. burgdorferi antibodies in blood. The health care provider will order at least two of three Lyme disease tests:
- Indirect Fluorescent Antibody (IFA)
- Enzyme-Linked Immunosorbent Assay (ELISA): This is the quickest and most sensitive test for Lyme disease.
- Western Blot Test: This test confirms positive IFA and ELISA test results.
The Lyme disease test can produce a false-negative result if performed within 2. months of the tick bite because the patient’s immune system may take 2. months to produce a detectable amount of B. burgdorferi bacteria antibodies. Likewise, test results can produce a false-positive result because B. burgdorferi bacteria antibodies remain in the patient’s blood years after the B. burgdorferi were killed.
The health care provider orders Lyme disease tests if the patient has symptoms of Lyme disease or is known to have been exposed to tick bites.

8. Rubella Test
The rubella test is used to assess if the patient is immune to the rubella virus or currently or has recently had a rubella virus infection.

Understanding the Rubella Test
Rubella (German measles) is a virus that causes congenital rubella syndrome (CRS) if a pregnant woman is infected with the rubella virus and transmits it to the fetus in the first trimester. Congenital rubella syndrome consists of birth defects and possibly a miscarriage or stillbirth. The rubella test detects rubella virus antibodies in the blood. There are two rubella virus antibodies that are detected:
- IgM Antibody: The patient currently has or recently had a rubella virus infection.
- IgG Antibody: The patient has immunity against the rubella virus. The rubella virus antibody developed from a previous rubella virus infection or from the rubella virus vaccination.

9. Syphilis Tests
Syphilis tests are used to assess if the patient is infected with syphilis and assess the treatment.

Understanding Syphilis Tests
Treponema pallidum is the bacterium that causes syphilis. The syphilis tests identify T. pallidum in a blood sample. There are seven types of syphilis tests:
. Venereal Disease Research Laboratory (VDRL): This test identifies anticardiolipin antibodies that are produced by a patient who has syphilis. Diseases including syphilis cause the production of anticardiolipin antibodies; therefore, this test is used for screening for syphilis and not diagnosing syphilis.
. Rapid Plasma Reagin (RPR): This test is similar to VDRL except antibodies can be detected without the aid of a microscope.
. Enzyme-linked Immunosorbent assay (ELISA): This test identifies T. pallidum and is used for screening for syphilis. An additional test is necessary to diagnose syphilis.
. Fluorescent Treponemal Antibody Absorption (FTA-ABS): This test identifies T. pallidum antibodies after the 4th week after the initial infection and is used to confirm other positive test results.
. Treponema pallidum Particle Agglutination Assay (TPPA): This test is similar to the FTA-ABS except it is not used to test spinal fluid.
. Darkfield Microscopy: This test identifies the T. pallidum bacterium under a darkfield microscope and is used to diagnose the early stage of syphilis.
. Microhemagglutination assay (MHA-TP): This test is similar to TPPA.
A positive VDRL or RPR test does not mean that the patient has syphilis. Other conditions can cause a positive test result. FTA-ABS, MHA-TP, and TPPA remain positive even after the patient is successfully treated for syphilis. VDRL and RPR tests are negative when treatment for syphilis is successful. A negative result does not rule out syphilis, since detectable antibodies can take 4. weeks to develop following the initial infection.
Many syphilis tests can use either a blood sample or a sample of spinal fluid.

Basic Questions
Infection Tests

1. Why are antibody tests administered?
Antibody tests are used to assess the underlying causes of autoimmune hemolytic anemia, blood transfusion reaction, or potential reaction, and screen for the Rh factor.

2. What are antibodies?
Antibodies are proteins made by the immune system that bind to bacteria, viruses, and other microorganisms to destroy the microorganism. Antibodies can also bind to red blood cells (RBCs), destroying them as well.

3. What is a blood transfusion reaction?
A blood transfusion reaction occurs when transfused blood has different antigens on the surface of its RBCs than the patient’s RBCs, which causes the immune system to produce antibodies that attack the transfused RBCs.

4. What is rhesus factor sensitization?
Rhesus factor sensitization occurs when the Rh antigen is in the fetus’s blood (Rh positive), but not the mother’s blood (Rh negative). During delivery, the fetus’s blood mixes with the mother’s blood, causing the mother’s immune system to create antibodies against the fetus’s RBCs. The mother becomes Rh sensitive. The antibodies can attack the fetus’s RBCs in future pregnancies if the fetus is Rh positive. Women with Rh-negative blood are given the Rh immune globulin (RhoGAM), which typically stops Rh sensitivity.

5. What is an Rh antibody titer?
Rh antibody titer is the test performed in early pregnancy to determine the mother’s blood type and if the mother is Rh negative.

6. What is the direct Coombs test?
The direct Coombs test identifies antibodies attached to the patient’s RBCs. This test is performed on a newborn whose mother is Rh negative to determine if the antibodies crossed the placenta into the newborn’s blood; a patient who received a blood transfusion to determine if there is a transfusion reaction; and a patient to determine if an autoimmune response is occurring.

7. What is the indirect Coombs test?
The indirect Coombs test identifies antibodies that have not but could attach to the patient’s red blood cells if the patient’s blood is mixed. This test is performed on the blood transfusion recipient or donor before the transfusion to identify if antibodies exist in his or her blood.

8. Why would a health care provider order a blood culture?
Blood cultures are used to assess the existence of bacteria or fungi in blood, endocarditis, medication that will kill the microorganism; the cause of unexplained fever; and the effect of treatment of a microorganism infection.

9. How is a blood culture performed?
Blood can be infected by bacteria or fungi. A blood culture identifies the bacteria or fungi by allowing the microorganism to grow in a controlled environment and then examining the microorganism under a microscope.

10. What is a sensitivity test?
A sensitivity test identifies medication that kills a microorganism.

11. What is the virus that causes mononucleosis?
The Epstein-Barr virus causes mononucleosis.

12. What is the monospot test?
The monospot test identifies heterophil antibodies that form between 2. and 9. weeks after the patient becomes infected.

13. When is the Epstien-Barr virus (EBV) antibody test ordered?
The EBV antibody test is ordered when the patient shows symptoms of mononucleosis and the monospot test is negative.

14. What is Helicobacter pylori?
H. pylori are bacteria that infect the stomach and duodenum, and may result in a peptic ulcer. Many patients have H. pylori, but few develop peptic ulcer disease.

15. What is the purpose of the urea breath test?
This test determines the presence of H. pylori in the stomach.

16. What is the H. pylori blood antibody test?
This test determines if the blood sample has H. pylori antibodies.

17. Why would H. pylori tests result in a false-positive result?
Blood tests for H. pylori antibodies may give a false-positive result since antibodies are present years after an H. pylori is resolved.

18. Why would H. pylori tests result in a false-negative result?
All tests may produce a false-negative result if the H. pylori count is low and undetectable.

19. What is a common term for herpes simplex virus type 1. (HSV-1)?
HSV-1. is commonly called a fever blister or cold sore that appears on the lips; it is spread by direct contact or indirectly through sharing eating utensils.

20. What is herpes simplex virus type 2. (HSV-2)?
HSV-2. is commonly called genital herpes; it appears on the penis or vagina and is spread by direct contact.

21. What is the purpose of the polymerase chain reaction (PCR) test?
This test differentiates between HSV-1. and HSV-2. in cell scraping.

22. What bacteria cause Lyme disease?
The Borrelia burgdorferi bacteria cause Lyme disease.

23. Why might the Lyme disease test produce a false-negative result?
Lyme disease test results can produce a false-negative result if performed within 2. months of the tick bite because the patient’s immune system may take 2. months to produce a detectable amount of B. burgdorferi bacteria antibodies.

24. When might the health care provider order Lyme disease tests?
The health care provider might order Lyme disease tests if the patient has symptoms of Lyme disease or is known to have been exposed to tick bites.

25. What might be concluded if the patient is positive for the IgM antibody?
The patient currently has or recently had a rubella virus infection.