False Positive Vs False Negative STD Test

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By Steve Page

The accuracy of the test depends on the type of STI, whether it is a blood or capillary test. For example, a test for a sexually transmitted infection (STI) might give a false positive more often than a true positive. Likewise, the number of true positives and false negatives may also differ between common and uncommon conditions. You should be aware of the differences and their treatment whichever test you use.

Statistics on rates of false negatives for common STDs:

  • Gonorrhea: According to the Centers for Disease Control and Prevention (CDC), nucleic acid amplification tests (NAATs) have a false-negative rate of less than 1%. However, false negatives are more likely to occur in the early stages of infection or if the infection is located in the throat or rectum.
  • Chlamydia: According to the CDC, NAATs have a false-negative rate of less than 1%. However, false negatives are more likely to occur in the early stages of infection or if the infection is located in the throat or rectum.
  • Syphilis: According to the CDC, false negatives can occur during the primary and secondary stages of syphilis, when the symptoms are not as severe. However, in later stages, when the symptoms are more severe, it is less likely to produce false negatives.
  • HPV: According to the National Cancer Institute, false negatives can occur with some types of HPV, specifically the high-risk types that can lead to cancer. These types are not detected by all HPV tests.

Capillary testing

There is a fine line between a false positive and a false negative STD test. Specificity and sensitivity refer to how accurate a test is at determining which people have a disease. The higher the sensitivity and specificity, the less likely it is to produce false results. False positives can result in unnecessary treatments and missed diagnoses of a serious disease, such as HIV. The lower the specificity and sensitivity, the greater the risk of false positives and false negatives.

The accuracy of a STD test depends on the condition and the frequency of infection. A more common STI may yield more false positive results than a more uncommon one. In addition to the test’s accuracy, treatment for STIs varies from one person to the next. Capillary testing is the most common type of STD test. However, it is not the only test available.

Blood tests

The first thing to understand about blood tests for STDs is the difference between a false positive and false negative. While false negatives are extremely rare, they do happen. In fact, the difference between a false positive and a false negative STD test may be as large as five points. False negatives are a sign of an underlying medical condition. If you suspect that you are infected with an STD, it’s important to get a second opinion. Although false negative results are a common problem, they are rarely fatal. Getting your test performed by a qualified STD testing facility is crucial.

The rate of false negative results for STI tests is higher than you might think. Most false negative results result from patient error. Moreover, you may get a false negative test result if you’ve had sex with someone before the recommended window period. That’s because no STD test is 100% accurate immediately after sex. That’s when the bacteria and viruses have the time to reach a detectable state. It’s also when your body’s immune system can show signs of infection.

PCR tests

The question of false positive vs false negative STD screening results can be confusing for clinicians. Although a positive test result can be interpreted as a negative result, a low-prevalence population may have lower PPV and hence, should be considered with caution. In addition, if a positive test result occurs, further testing should be considered to rule out other causes of the disease.

Both urine and intraurethral swab specimens can be tested with a PCR test. Many STD specialists believe that swab specimens are more sensitive, but limited published evaluations have failed to support this claim. In addition, males without urethritis may not be willing to undergo such an invasive test. Generally, urine NAATs have adequate sensitivity for screening purposes. Moreover, non-NAATs have low sensitivity for C. trachomatis.

STI test sensitivity

The sensitivity of STI tests depends on the type of STI and the person taking the test. Tests with a higher sensitivity may have more false-positive results than those with low sensitivity. For example, a test with a 99% sensitivity could result in a diagnosis of one infected person while one uninfected person would receive a false-negative result. Conversely, a test with a low sensitivity may result in a false-negative result, meaning the person tested has a disease when in reality they do not.

In clinical practice, the sensitivity of an STI test varies significantly, depending on the method used. Generally, test sensitivity for N. gonorrhoea is 90%. However, the test sensitivity for C. trachomatis and E. coli is 86%. It is difficult to determine the sensitivity of an STI test for gonorrhoea in men.

Frequently Asked Questions

How common are false negative STD tests?

False negative results are more common for some types of STDs than others. For example, for Gonorrhea and Chlamydia, false negatives are more likely to occur in the early stages of infection or if the infection is located in the throat or rectum. In the case of these two STDs, nucleic acid amplification tests (NAATs) are considered to be the most accurate and are less likely to produce false-negative results.

For syphilis, false negatives can occur during the primary and secondary stages, when the symptoms are not as severe. In these stages, syphilis can be mistaken as another skin condition. However, in later stages, when the symptoms are more severe, it is less likely to produce false negatives.

For HPV, false negatives can occur with some types of HPV, specifically the high-risk types that can lead to cancer. These types are not detected by all HPV tests.

False negatives can also occur if the test is performed too soon after exposure to the infection, as it may take a few days or weeks for the body to produce enough of the virus or bacteria for the test to detect it.

Can antibiotics cause false positive STD tests?

Antibiotics do not typically cause false positive results on STD tests. It is recommended to wait a certain period of time after treatment before getting tested.

Can BV cause a false positive chlamydia test?

BV can cause changes in the vaginal environment and may affect the results of tests for other STDs, such as chlamydia. In some cases, BV can cause false positive test results for chlamydia. This is because the symptoms of BV and chlamydia can be similar, and the tests used to diagnose both conditions are similar.

When a test for chlamydia is performed, it is looking for the presence of chlamydia trachomatis bacteria in the sample. If a person has BV, the test may pick up the presence of other bacteria that are present in the sample, resulting in a false positive result.

Therefore, if a person has a positive chlamydia test result, but no symptoms, and they have BV, the healthcare provider should repeat the test or use another test that is more specific to confirm the diagnosis.

Can you get a false positive chlamydia test?

It is possible to get a false positive result on a chlamydia test, although it is rare. False positive results occur when a test incorrectly indicates that a person has an infection when they do not. There are several potential causes of false positive results for chlamydia tests, including:

– Cross-reactivity: Some tests detect antibodies or antigens that can cross-react with other microorganisms, leading to a false positive result.

– Laboratory error: A false positive result can occur due to errors in the laboratory, such as contamination of the sample or mistakes in the testing process.

– False positive from other infections: Some other infections can cause a false positive result for chlamydia, such as Mycoplasma genitalium or Ureaplasma.

– False positive from other medical conditions: Some medical conditions can cause a false positive result for chlamydia, such as inflammatory bowel disease.

Can pregnancy cause a false positive chlamydia test?

Pregnancy itself is unlikely to cause a false positive result on a chlamydia test. However, there are a few potential ways in which pregnancy can affect chlamydia testing:

– Hormonal changes: Pregnancy can cause hormonal changes in the body, which can affect the cervix and increase the risk of false negative results.

– Increased cervical secretions: Pregnancy can cause an increase in cervical secretions, which can make it more difficult to obtain a sample for testing.

– Interference with test results: Some medications or supplements taken during pregnancy can interfere with test results, leading to a false positive result.

What does a false positive chlamydia test mean?

A false positive result on a chlamydia test means that the test has indicated that a person has an infection when they do not. This can occur due to a number of reasons, such as:

– Cross-reactivity: Some tests detect antibodies or antigens that can cross-react with other microorganisms, leading to a false positive result.

– Laboratory error: A false positive result can occur due to errors in the laboratory, such as contamination of the sample or mistakes in the testing process.

– False positive from other infections: Some other infections can cause a false positive result for chlamydia, such as Mycoplasma genitalium or Ureaplasma.

– False positive from other medical conditions: Some medical conditions can cause a false positive result for chlamydia, such as inflammatory bowel disease.

It’s important to note that a false positive result does not mean that a person does not have chlamydia, it just indicates that the test is not conclusive. If the test results are positive, it’s essential to be retested and to consult with a healthcare provider to determine the cause of the false positive result.

Can antibiotics cause a false negative STD test?

Antibiotics can cause a false negative result on an STD test, particularly for bacterial infections such as chlamydia and gonorrhoea.

This is because antibiotics work by killing or inhibiting the growth of bacteria. If a person is taking antibiotics at the time of the test, the bacteria that cause chlamydia and gonorrhoea may have already been killed, which can lead to a false negative result.

How common are false negative STD tests?

False negative results on STD tests can occur, but their frequency depends on the type of test and the specific STD being tested for.

For example, false negative results are more common for tests that detect the presence of antibodies, such as HIV tests. This is because it can take weeks or even months for the body to produce enough antibodies for the test to detect, so if a person is tested too soon after infection, they may receive a false negative result.

False negative results are also more common for tests that detect the presence of the actual pathogen, such as chlamydia and gonorrhoea. This is because the number of bacteria present in the body might be too low to be detected by the test, especially if a person has been recently treated with antibiotics or is in the very early stage of the infection.

Additionally, the location of the infection is also important, for example, a test done on urine samples will not detect infections in the throat or rectum.

Overall, the rate of false negative results varies widely, depending on the specific test, the stage of the infection, and the population being tested. In general, newer and more sensitive tests have lower rates of false negatives, but it’s always important to retest if there is a high chance of having contracted an STD, especially in case of symptoms.