Serology is the scientific study of plasma serum and other bodily fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum. Such antibodies are typically formed in response to an infection (against a given microorganism), against other foreign proteins (in response, for example, to amismatched blood transfusion), or to one's own proteins (in instances of autoimmune disease).
Serological tests may be performed for diagnostic purposes when an infection is suspected, in rheumatic illnesses, and in many other situations, such as checking an individual's blood type. Serology blood tests help to diagnose patients with certain immune deficiencies associated with the lack of antibodies, such as X-linked agammaglobulinemia. In such cases, tests for antibodies will be consistently negative.
There are several serology techniques that can be used depending on the antibodies being studied. These include: ELISA, agglutination, precipitation, complement-fixation, and fluorescent antibodies.
Some serological tests are not limited to blood serum, but can also be performed on other bodily fluids such as semen and saliva, which have (roughly) similar properties to serum.
The ASO test is primarily ordered by itself or along with an anti-DNase B to help determine whether a person has had a recent streptococcal infection. In most cases, strep infections are identified and treated with antibiotics and the infections resolve. In cases where they do not cause identifiable symptoms and/or go untreated, however, post-streptococcal complications (sequelae), namely rheumatic fever and glomerulonephritis, can develop in some patients, especially young children. The test, therefore, is ordered if a person presents with symptoms suggesting rheumatic fever or glomerulonephritis and has had a recent history of sore throat or a confirmed streptococcal infection. Since the incidence of post-streptococcal complications has dropped in the U.S., so has the use of the ASO test.
C-reactive protein (CRP) is a non-specific test. It is used by a doctor to detect inflammation if there is a high suspicion of tissue injury or infection somewhere in the body, but the test cannot tell where the inflammation is or what condition is causing it. CRP is not diagnostic of any condition, but it can be used together with signs and symptoms and other tests to evaluate an individual for an acute or chronic inflammatory condition.
For example, CRP may be used to detect or monitor significant inflammation in an individual who is suspected of having an acute condition such as:
• A serious bacterial infection like sepsis or a fungal infection
• Pelvic inflammatory disease (PID)
The CRP test is useful in monitoring people with chronic inflammatory conditions to detect flare-ups and/or to determine if treatment is effective. Some examples include:
• Inflammatory bowel disease
• Some forms of arthritis
• Autoimmune diseases, such as lupus or vasculitis
CRP may sometimes be ordered along with an Erythrocyte Sedimentation Rate (ESR), another test that detects inflammation. While the CRP test is not specific enough to diagnose a particular disease, it does serve as a general marker for infection and inflammation, thus alerting medical professionals that further testing and treatment may be necessary. Depending on the suspected cause, a number of other tests may be performed to identify the source of inflammation.
The rheumatoid factor (RF) test is primarily used to help diagnose rheumatoid arthritis (RA) or Sjögren syndrome and to help distinguish them from other forms of arthritis or other conditions that cause similar symptoms. While diagnoses of RA and Sjögren syndrome rely heavily on the clinical picture, some of the signs and symptoms may not be present or follow a typical pattern, especially early in these diseases. Furthermore, the signs and symptoms may not always be clearly identifiable since people with these diseases may also have other connective tissue disorders or conditions, such asRaynaud's phenomenon, scleroderma, autoimmune thyroid disorders, and systemic lupus erythematosis, and display symptoms of these disorders as well. The RF test is one tool among others that can be used to help make a diagnosis when RA or Sjörgren syndrome is suspected.
The RF test may be ordered along with other autoimmune-related tests, such as an ANA (antinuclear antibody), and other markers of inflammation, such as a CRP (C-reactive protein) and ESR (erythrocyte sedimentation rate), as well as a CBC (Complete Blood Count) to evaluate the body's blood cells. A CCP (Cyclic Citrullinated Peptide Antibody) test, a relatively new test that can help detect early RA, may be ordered if the RF is negative.
The RF test may also be ordered, along with tests such as anti-SS-A and anti-SS-B to help diagnose Sjögren syndrome.
The tests are used to screen for and diagnose infection with Treponema pallidum, the bacterium that causes syphilis. Screening of all pregnant women is recommended by the US Preventive Services Task Force, preferably at the first prenatal visit. Many states require a blood test for syphilis when a couple is applying for a marriage license in order to help prevent the spread of the infection to others, especially a newborn baby.
There are several methods that can be used to test for syphilis. One method used in diagnosis of early cases involves looking for the bacterium in scrapings from the chancre using a special instrument called a dark-field microscope. Other methods require a blood sample in which antibodies can be detected. These include:• For screening – VDRL which stands for “venereal disease research laboratory” test and rapid plasma reagin test (RPR)
A method called microhemagglutination assay, MHA-TP, is rarely used any more.
Response to treatment can be determined with a follow-up RPR test, and the FTA-ABS test is used to confirm a positive VDRL or RPR screening test. In late or latent syphilis, cerebrospinal fluid (CSF) may be obtained using a spinal tap and then tested in order to diagnose brain involvement (neurosyphilis).
The Widal test is one method that may be used to help make a presumptive diagnosis of enteric fever, also known as typhoid fever. Although the test is no longer commonly performed in the United States or other developed countries, it is still in use in many developing countries where enteric fever is endemic and limited resources require the use of rapid, affordable testing alternatives.
The mono test is used to help determine whether a person with symptoms has infectious mononucleosis (mono). It is frequently ordered along with a complete blood count (CBC). The CBC is used to determine whether the number of white blood cells (WBCs) is elevated and whether a significant number of reactive lymphocytes are present. Mono is characterized by the presence of atypical white blood cells.
If the mono test is initially negative but the doctor still suspects mono, a repeat test done a week or so later may be used to determine whether heterophile antibodies have developed. If the mono test is persistently negative, a test specific for EBV antibodies may be used to help confirm or rule out the presence of an EBV infection.
A strep test may also be ordered along with a mono test to determine whether a person's sore throat is due to strep throat (group A streptococcal infection) instead of or in addition to mononucleosis.
A toxoplasmosis test may be performed on a woman prior to or during a pregnancy to determine if she has been previously exposed to Toxoplasma gondii and during a pregnancy if exposure is suspected. It may also be ordered to help detect an infection in someone who is immunocompromised and has flu-like symptoms, or in someone who has signs orsymptoms of toxoplasmosis. Amniotic fluid may sometimes be tested to detect and diagnose infection in an unborn child.
There are several methods of testing for T. gondii. The choice of tests and samples collected depends on the patient, their symptoms, and on the doctor's clinical findings.Antibody Testing
IgM antibodies are the first to be produced by the body in response to a Toxoplasma infection. They are present in most individuals within a week or two after the initial exposure. IgM antibody production rises for a short time period and declines. Eventually, sometimes months after the initial infection, the level (titer) of Toxoplasma IgM antibody falls below detectable levels in most people. Additional IgM may be produced when dormant T. gondii is reactivated and/or when a person has a chronic infection. IgM antibodies are the only type produced by the fetus. When they are present in a newborn, they indicate a congenital infection.
IgG antibodies are produced by the body several weeks after the initial infection to provide long-term protection. Levels of IgG rise during the active infection, then stabilize as the Toxoplasma infection resolves and the parasite becomes inactive. Once a person has been exposed to T. gondii, they will have some measurable amount of IgG antibody in their blood for the rest of their life. T. gondii IgG antibody testing can be used, along with IgM testing, to help confirm the presence of a recent or previous Toxoplasma infection.
Antibody testing may sometimes be performed as part of a TORCH panel. TORCH is an acronym for several infections that can affect an unborn child and typically includes testing for: Toxoplasmosis, Rubella, Cytomegalovirus, and Herpes simplex virus.Molecular Detection
Molecular testing may be performed to detect and measure T. gondii DNA in a blood, CSF or amniotic fluid sample.
Other tests, such as an IgG avidity test, may be performed by a reference laboratory to help confirm a T. gondii infection. Tests such as a tissue culture or biopsy stain are rarely done.
Cytomegalovirus (CMV) testing is used to determine whether someone with signs and symptoms has an active infection. Sometimes it may be ordered to help determine whether someone had a prior infection and is therefore immune to a primary infection.
There are a few different methods of detecting a CMV infection:
Antibody testing can be used to determine if someone has had recent or past exposure. There are two types of CMVantibodies that are produced in response to a CMV infection, IgM and IgG, and one or both may be detected in the blood.
CMV antibody testing may be used to determine immunity to primary CMV infections in people prior to organ or bone marrow transplantation and in a person diagnosed with HIV/AIDS. Since CMV infection is widespread and causes few problems to those with healthy immune systems, general population screening is rarely done.
Antibody testing and viral CMV detection may be used to help diagnose primary CMV infection in young adults, pregnant women, and some immune-compromised people with flu- or mononucleosis-like symptoms. By comparing the absence or presence of IgG and IgM antibodies in the same sample or the amount of antibody present in samples collected on different days, the doctor may be able to distinguish between active and latent CMV.
Testing for IgM antibodies may be used to detect a congenital infection in a newborn. Tests that detect the virus directly must be performed to confirm the diagnosis.
Viral detection involves determining the presence of CMV in a blood, fluid, or tissue sample. This can be done either byculturing the virus or by detecting the virus's genetic material (CMV DNA).
Viral culture is the traditional method of virus detection. Presence of the virus (positive cultures) can often be determined in as little as 1 to 2 days, but cultures that are negative for the virus must be held for 3 weeks to confirm the absence of CMV because the virus may be present in very low numbers in the original sample and/or the CMV strain may be slow-growing.
Molecular methods may be used to detect and measure the amount of viral DNA in a person's sample. Testing can bequalitative, determining the presence or absence of CMV, or quantitative, measuring the amount of virus present.
The choice of tests and samples collected depends on the age of the person, their general health status and symptoms, and on the doctor's clinical findings and suspicions of organ involvement. For instance, a newborn's urine may be cultured to detect CMV, while a pregnant woman may have IgG and IgM blood testing to identify the presence of antibodies and to distinguish between a current primary infection and a previous infection.
Immune-compromised people with active CMV may be monitored using a variety of CMV tests. Often doctors want a quantifiable viral test to be able to track the amount of virus present (viral load). They can use a quantitative test to monitor a person's response to antiviral therapy.
HSV testing is used to detect the presence of the herpes simplex virus in those who have genital sores, encephalitis, and in newborns suspected of having neonatal herpes, a rare but serious condition in which herpes is contracted during birth. A pregnant woman who has been diagnosed with herpes may be monitored regularly prior to delivery to identify a reactivation of her infection, which would indicate the necessity for a caesarean section to avoid infecting the baby.
The primary methods of testing for the virus are the herpes culture and HSV DNA testing. Although it is not as sensitive, HSV antibody testing can be used to help diagnose an acute HSV infection if acute and convalescent blood samples are collected. The convalescent blood sample is collected several weeks after the acute sample, and HSV IgG antibody levels are compared to see if they have risen significantly, indicating a current infection. Antibody testing may also be used to screen certain populations, such as sexually active people, potential organ transplant recipients, and those with HIV/AIDS, for a previously contracted HSV infection.
The rubella test is used to:
A rubella test may be ordered on a person, pregnant or not, who has symptoms that the doctor suspects are due to a rubella infection. It may also be ordered on a newborn who is suspected to have become infected during pregnancy or that presents with congenital birth defects that the doctor suspects may be due to a rubella infection.
The IgG rubella test is ordered when a woman is pregnant or is planning on becoming pregnant. It is ordered whenever a check of immunity against rubella is required. IgM and IgG rubella tests are ordered when a pregnant woman has signsand symptoms that may indicate a rubella infection.
Some signs and symptoms include:
Since many conditions can cause similar symptoms, the doctor will need to order the tests in order to confirm the diagnosis.
IgM and IgG tests may be ordered on a newborn when the mother was diagnosed with a rubella infection during pregnancyand/or when a newborn is born with birth defects such as hearing loss, cardiovascular abnormalities, cataracts, and/or central nervous system disease that could be due to CRS.
Since IgM and IgG rubella antibodies take some time to appear after infection, the tests may be repeated in 2 to 3 weeks to see if the antibody levels have become detectible (when initially absent) and to determine whether the levels are rising or falling over time.
This test may be required of a health care worker or a person starting college and is still ordered on women in some states as part of the blood testing required to obtain a marriage license.
In an adult or child, the absence of IgG rubella antibodies means that the person likely has not been exposed to the rubella virus or been vaccinated and is not protected against it. The presence of IgG antibodies but not IgM antibodies indicates a history of past exposure to the virus or vaccination and indicates that the person tested should be immune to the rubella virus. The presence of IgG antibodies, but not IgM antibodies, in a newborn means that the mother's IgG antibodies have passed to the baby in utero and these antibodies may protect the infant from rubella infection during the initial six months of life. The presence of IgM antibodies in a newborn indicates that the baby was infected during pregnancy because the mother’s IgM antibodies do not pass to the baby through the umbilical cord. The presence of IgM antibodies, with or without IgG antibodies, in a child or adult indicates a recent infection with the rubella virus.
Occasionally, a person may have a false positive test for IgM rubella antibodies because the test components cross react with other proteins in their body. To confirm the IgM result, the doctor may order an IgG test to establish a baseline level of antibody and may repeat the IgG test again in 2-3 weeks to look for a significant increase in the amount (titer) present, indicating a recent rubella infection.
HIV antibody testing is used to screen for and diagnose HIV infections. Since there is no cure, early treatment of HIV infection and immune system monitoring can greatly improve long-term health and survival. Also, if a person knows his HIV status, it may help change behaviors that can put him and others at risk.
Different types of antibody tests may be used for HIV screening:
Various options are available for getting tested:
Regardless of the type of screening test used, a positive result requires follow up with a second test to establish a diagnosis of HIV. Current testing protocols usually involve an initial screening test that uses a method called animmunoassay (IA). If positive, the HIV antibody immunoassay test is repeated. It is a very sensitive type of test but currently requires a second test method, usually a Western blot, to confirm the results because false positives can occur.
With the aim of improving the diagnostic process, a new testing protocol has been proposed and is in the process of being implemented. Over time, more clinics and doctors may opt to follow these steps:
This test is used to diagnose infection due to Helicobacter pylori. A positive test for H. pylori indicates that a person's gastrointestinal pain may be caused by a peptic ulcer due to this bacterium. Treatment with a combination of antibiotics and other medications will be prescribed to kill the bacteria and stop the pain and the ulceration.
Testing for H. pylori may be repeated following several weeks of treatment to determine if it was effective. However, the blood antibody test cannot be used for this purpose since antibodies to H. pylori may persist even after an infection is resolved; usually the stool or breath test will be used for this purpose.
An acute hepatitis panel is used to help detect and/or diagnose an acute liver infection due to one of the three most common hepatitis viruses: Hepatitis A virus (HAV), Hepatitis B virus (HBV), or Hepatitis C virus (HCV). There are several causes of hepatitis and the accompanying symptoms, so these tests are used to determine if symptoms are due to a current infection with a virus and to identify which virus in particular is causing the disease. These tests may also help determine if someone has been exposed to one of the viruses even before symptoms develop. An acute hepatitis panel typically consists of the following tests:
In acute hepatitis, other tests such as a liver panel or individual tests such as bilirubin, ALT, and AST, may be performed to help diagnose the condition.
There are some other tests that may be offered as part of a hepatitis panel, depending on the laboratory performing the tests. These may include:
An acute viral hepatitis panel may be ordered when a person has had blood tests done as part of a health checkup that show abnormal results on liver tests or when someone has acute symptoms associated with liver damage such as:
In the presence of acute symptoms such as those listed above, a positive result on the test for Hepatitis A IgM antibodiesis considered diagnostic for acute infection with Hepatitis A. However, the Centers for Disease Control and Prevention (CDC) have recommended against using the test for screening in those without acute hepatitis symptoms to prevent falsely positive results. The acute viral hepatitis panel may sometimes be used to screen people who are at an increased risk for Hepatitis B or C infection or if it is known that they have been exposed. Below are listed some examples of who may be screened using the panel:
The table below summarizes results that may be seen with a hepatitis panel that is performed to detect an acute infection:
If other hepatitis tests are performed to help determine prior exposure or previous infection, they may indicate the following:
It is possible to be infected with more than one hepatitis virus, and an acute infection with one hepatitis virus can be superimposed on a chronic infection with a different hepatitis virus. In such cases, there may be a positive result for more than one type of virus and care must be taken when interpreting the results. If all the viral tests are negative, then the antibody or antigen level is too low to detect or the hepatitis is due to some other cause. For more on this and other tests that may be done to determine the cause, see the article on Hepatitis.
A semen analysis is used to determine whether a man might be infertile—unable to get a woman pregnant. The semen analysis has many parts and tests a lot of aspects of the semen and sperm. A semen analysis to determine fertility should be performed on a minimum of two samples at least seven days apart over a period of two to three months because the sperm count and semen consistency will vary from day to day and some conditions can temporarily affect sperm levels.
The semen analysis also can be used to count sperm after a man has a vasectomy. If there are still sperm present in the semen, whether alive and still motile or apparently dead, the man and his partner will have to take precautions so that the woman does not become pregnant. He will have to return for one or more sperm counts until sperm are no longer present in his sample(s).
A semen analysis is performed when a physician thinks that a person or couple might have a fertility problem. At least 10%-20% of married couples experience problems conceiving. Male factors are implicated about 30% of the time and combined male and female factors about 20% of the time. Male infertility has many causes and some of these, such as enlargement of the veins draining the testes (varicocele), can be treated successfully. If male factors are involved, analysis of the semen is necessary to determine what is inhibiting fertility and, when indicated, to evaluate the feasibility of using assisted reproductive technology to facilitate pregnancy. When a semen analysis is abnormal, then the test is repeated at intervals determined by the doctor.
A semen analysis is typically ordered following a vasectomy and repeated as necessary until sperm are no longer present in the semen sample.
The typical volume of semen collected is around one-half to one teaspoonful (2-6 milliliters) of fluid. Less semen would indicate fewer total sperm, which may affect fertility. More semen indicates too much fluid, which may dilute the concentration of sperm. The semen should initially be thick and then liquefy within 10 to 30 minutes. If this does not occur, then it may impede sperm movement.
Sperm concentration (also called sperm density) is measured in millions of sperm per milliliter (mL) of semen. Normal is 20 million or more sperm per mL, with a total of 80 million or more sperm in one ejaculation. Fewer sperm and/or a lower sperm concentration may impair fertility. Following a vasectomy, the goal is to have no sperm detected in the semen sample.
Motility is the percentage of moving sperm in a sample and an evaluation of their rate and direction of travel. At least 50% should be motile one hour after ejaculation, and they should be moving forward in a straight line with good speed. The progression of the sperm is rated on a basis from zero (no motion) to 4, with 3-4 representing good motility. If less than half of the sperm are motile, a stain is used to identify the percentage of dead sperm. This is called a sperm viability test.
Morphology analysis is the study of the size, shape, and appearance of the sperm cells. The analysis evaluates the structure of 200 sperm, and any defects are noted. The more abnormal sperm that are present, the lower the likelihood of fertility. Abnormal forms may include defective heads, middles, tails, and immature forms. To see an image of a normal sperm, see the MedlinePlus Medical Encyclopedia page on sperm.
Semen pH should be between 7.2 and 7.8, fructose at 150-600 mg/dL, and there should be less than 2000 white blood cells per mL.
When a doctor is evaluating a man's fertility, each aspect of the semen analysis is considered, as well as the findings as a whole. Each part of the semen analysis either contributes to fertility or lessens it, but the results do not necessarily predict the eventual outcome. Couples with poor results may still conceive, with or without assistance, and those with apparently good results may experience difficulties.
Several factors can affect the sperm count and other semen analysis values. A man may have a lower sperm count if he has physical damage to the testicles, has gone through radiation treatment of his testicles, or has had exposure to certain drugs (such as azathioprine or cimetidine). A man with a higher level of estrogens may have lower sperm counts.
Some of the common causes of male infertility are extremely high fever, failure of the testicles, obstruction of the tubes that carry semen to the penis, and a less than normal amount of sperm in the sample (oligospermia).