Syphilis blood test: timing, types of tests, and results

A blood test for syphilis does not directly detect the bacteria itself, but rather the antibodies produced by the immune system in response to infection with Treponema pallidum. Serological diagnostics remain the primary laboratory method for detecting syphilis in people without visible lesions, in latent infections, and after the primary ulcer or secondary rash has resolved. [1]

There is no single, universal test that can simultaneously confirm active infection, determine its duration, and demonstrate the success of treatment. For a reliable diagnosis, two groups of tests must be combined: treponemal tests, which detect antibodies to Treponema pallidum, and non-treponemal tests, which detect antibodies to lipid antigens that arise during tissue damage. [2]

A positive treponemal test indicates that the organism has ever been exposed to Treponema pallidum. This may correspond to a current untreated infection, previously successfully treated syphilis, or, less commonly, a false-positive reaction. Therefore, a positive treponemal test cannot be interpreted separately from the treatment history and quantitative non-treponemal testing. [3]

Non-treponemal tests reflect the activity of the inflammatory process approximately, and the result is given not only as “positive” or “negative,” but also as a titer, for example, 1:4, 1:8, 1:16, or 1:32. It is the change in titer that is used for monitoring after treatment, assessing possible re-infection, and identifying probable treatment failure. [4]

The result is always evaluated in conjunction with symptoms, date of possible infection, previous tests, treatment history, pregnancy, and risk of re-exposure. Even a properly performed test does not replace a clinical assessment, because at the very beginning of primary syphilis, antibodies may not yet be detectable. [5]

What you need to know	What research helps?	The main limitation
Was there contact with Treponema pallidum?	Treponemal test	Often remains positive after treatment
How active is the infection?	Quantitative nontreponemal test	May be a false positive
Did the treatment help?	Comparison of non-treponemal titers	The titer decreases at different rates
Is a new infection possible?	New titer increase and clinical evaluation	A comparison with the previous result is required.
Is this very early syphilis?	Re-analysis and examination of the ulcer	The first blood test may be negative.

The table reflects the principle of combined use of treponemal and nontreponemal tests recommended by the US Centers for Disease Control and Prevention. [6]

What blood tests are used?

Nontreponemal tests are primarily represented by the rapid plasma reagin test and the sexually transmitted disease laboratory test. They detect antibodies to lipid antigens that arise as a result of the interaction of infection, the immune system, and damaged cell membranes. [7]

Nontreponemal tests are used for initial screening in the traditional algorithm, quantitative titer assessment, and post-therapy monitoring. Their advantage is that the titer typically declines after successful treatment, while the main disadvantage is the possibility of false-positive and false-negative results. [8]

Treponemal tests include enzyme-linked immunosorbent assays (ELISA), chemiluminescent immunoassays (CIA), the passive agglutination assay of Treponema pallidum particles, the hemagglutination assay, and the fluorescent treponemal antibody absorption test. These methods detect antibodies directed directly against Treponema pallidum antigens. [9]

Treponemal tests are generally more specific for treponemal infection, but are not suitable for monitoring the effectiveness of treatment. In most people, they remain positive for life, regardless of whether the infection has been completely cured, so repeating the test one month after treatment does not indicate whether the bacteria have disappeared. [10]

Some people treated for primary syphilis may eventually experience negative treponemal tests. According to the US Centers for Disease Control and Prevention, this occurs in approximately 15-25% of patients within 2-3 years, but this change cannot be relied upon as a criterion for cure. [11]

Test group	What does it reveal?	Main application	Suitable for treatment monitoring
Rapid plasma reagin test	Antibodies to lipid antigens	Screening and quantitative titer	Yes
Sexually Transmitted Diseases Laboratory Test	Antibodies to lipid antigens	Diagnosis and examination of cerebrospinal fluid	Yes
Enzyme-linked immunosorbent assay	Treponemal antibodies	Automated screening	No
Chemiluminescent immunoassay	Treponemal antibodies	Automated screening	No
Agglutination of Treponema pallidum particles	Specific treponemal antibodies	Confirmation of controversial results	No
Fluorescent treponemal antibodies	Specific antibodies	Additional confirmation	No

The differences between the two groups of tests and the need for their combined use are detailed in the 2024 laboratory guidelines. [12]

Traditional and reverse diagnostic algorithms

With the traditional algorithm, the laboratory first performs a non-treponemal test. If it is reactive, the sample is tested with a treponemal test to confirm that the detected antibodies are indeed related to syphilis and not to pregnancy, an autoimmune disease, vaccination, or another infection. [13]

The advantage of the traditional sequence is its relative simplicity and the ability to immediately obtain a quantitative titer. The disadvantage is that in very early or late latent syphilis, the non-treponemal test is sometimes negative, so the infection may be missed. [14]

In the reverse algorithm, an automated treponemal assay is performed first. If it is positive, the laboratory must perform a quantitative nontreponemal test, which helps determine the activity of the infection and creates a baseline titer for subsequent monitoring. [15]

If the initial treponemal test is positive but the nontreponemal test is negative, a second treponemal test of a different type, preferably using a different set of antigens, is required. This additional testing helps differentiate between previously treated syphilis, current latent infection, and a false-positive initial screening result. [16]

Both algorithms are considered acceptable. The choice depends on the laboratory's equipment, the number of tests, the prevalence of syphilis, and the organization of the medical service, but the clinician ultimately needs the results of both sets of tests, not the isolated result of one method. [17]

Stage	Traditional algorithm	Reverse algorithm
First study	Non-treponemal test	Automated treponemal test
The second stage if the result is positive	Confirmatory treponemal test	Quantitative nontreponemal test
Controversial result	Additional clinical assessment	Second treponemal test of a different type
The main advantage	The title is immediately available	Better detection of some early and latent infections
The main disadvantage	May miss early or late syphilis	More controversial results in low-risk groups

The traditional and reverse algorithm designs are consistent with current laboratory guidelines from the US Centers for Disease Control and Prevention. [18]

When to donate blood after possible infection

Immediately after infection, a blood test may be negative, as the immune system requires time to produce detectable amounts of antibodies. The primary ulcer usually appears approximately 3 weeks after exposure, but the incubation period can range from 9-10 to 90 days. [19]

Antibodies detected by treponemal and nontreponemal tests sometimes become detectable only some time after the primary infection has developed. Laboratory guidelines indicate that the formation of detectable antibodies may take up to 2 weeks after the onset of primary syphilis, so a very early ulcer may be associated with negative serology. [20]

If a person develops a chancre-like ulcer, they should be examined immediately, without waiting for the window period to end. If the test is negative, British guidelines recommend repeating the serological test after 2 weeks, especially if the ulcer discharge also does not reveal the pathogen. [21]

After recent asymptomatic sexual contact, early testing can be useful as a baseline, but a negative result is not always definitive. Different sexual health services use follow-up periods of up to 12 weeks after the last risk exposure, as serological responses can develop slowly in some cases. [22]

If exposed to someone with confirmed early syphilis, a doctor may recommend testing and preventive treatment without waiting for a positive result. The approach depends on the duration of exposure, symptoms, pregnancy, the likelihood of further monitoring, and the partner's test results. [23]

Situation	When to get examined	Is a repeat necessary?
An ulcer has appeared on the genitals, in the mouth, or around the anus	Immediately	Yes, if the first test is negative
Recent risk without symptoms	You can take the initial test now.	Monitoring is often required for up to 12 weeks.
Contact with confirmed early syphilis	As quickly as possible	By doctor's decision
The first analysis was performed before 12 weeks	The result may be preliminary.	Repeat is usually recommended
There is a rash on the palms or soles	Immediately	Additional tests based on the results
Pregnancy and possible contact	Immediately	According to the obstetric and infectious protocol

Timing of retesting depends on the clinical situation; waiting until the end of the window period is not recommended for ulcers, rashes, pregnancy, or known exposure.[24]

How to decipher combinations of results

A positive treponemal and positive nontreponemal test usually correspond to current syphilis or a previously treated infection with a persistent nontreponemal titer. To differentiate between these options, a physician evaluates previous tests, treatment history, titer changes, symptoms, and the possibility of new infection. [25]

A positive treponemal and negative non-treponemal result is possible after successful treatment, in late latent syphilis, at a very early stage of infection, or with a false-positive initial test. This is why the reverse algorithm requires a second treponemal test of a different type. [26]

If the second treponemal test is also positive and there has been no confirmed treatment in the past, the person is usually offered treatment for syphilis. In the absence of signs of recent infection, the infection is often classified as syphilis of unknown duration or late latent syphilis.[27]

If the initial treponemal test is positive, the nontreponemal test is negative, and the second treponemal test is also negative, then, in cases of low clinical and epidemiological risk, the result is often considered a false positive. Additional treatment is usually not required in this situation. [28]

A positive nontreponemal and negative treponemal result is most often a biological false-positive reaction. Such a response can occur with other infections, autoimmune diseases, pregnancy, recent vaccination, injection drug use, and some other conditions. [29]

Treponemal test	Non-treponemal test	Possible explanation	The next step
Positive	Positive	Current or previously treated syphilis	Study the titer, treatment history and symptoms
Positive	Negative	Previously treated, early or late infection	Perform a second treponemal test
Positive first and second	Negative	Post-exposure or latent syphilis	Check treatment and risk of re-infection
Positive first, negative second	Negative	Possible false positive result	Assess the risk, sometimes repeat the analysis
Negative	Positive	Biologically false positive reaction	Look for confirmation and a possible cause
Negative	Negative	No infection detected	Consider the window period and symptoms

The final diagnosis is based not on a single line of the laboratory form, but on the sequence of tests, the medical history and the likelihood of recent infection. [30]

What does the non-treponemal titer mean?

The titer indicates the highest dilution of the serum at which the reaction remains positive. For example, a result of 1:32 means that antibodies are detected after a 32-fold dilution of the sample, while 1:4 means after a 4-fold dilution. The higher the second number, the higher the concentration of detectable antibodies, but the titer does not equal the number of bacteria. [31]

A high titer is more common in early active syphilis, but the titer alone cannot reliably determine the stage. A patient with a late infection may have a low titer, and in a previously treated individual, mild reactivity can persist for years. [32]

A fourfold change in titer, which corresponds to two successive dilutions, is considered clinically significant. For example, a decrease from 1:32 to 1:8 is considered fourfold, while a decrease from 1:32 to 1:16 is only twofold and does not reach the accepted criterion. [33]

For accurate comparison, it is advisable to use the same type of non-treponemal test, preferably in the same laboratory. Results from the rapid plasma reagin test and the STD laboratory test cannot be considered completely interchangeable, as their titers may differ. [34]

After treatment, the titer usually gradually declines, but the rate depends on the stage of syphilis, the initial value, age, previous episodes of infection, and the individual immune response. The lack of rapid, complete disappearance of antibodies does not always mean that treatment was ineffective. [35]

Original titer	New title	Change	Possible interpretation
1:32	1:16	Decrease by 2 times	Not enough for the fourfold criterion
1:32	1:8	A 4-fold reduction	Clinically significant reduction
1:32	1:4	8 times reduction	Marked decrease
1:4	1:16	4 times growth	Possible re-infection or treatment failure
1:8	1:8	No change	Requires assessment of observation period and stage
1:2	Negative	Serological negativity	Possible after successful treatment

A fourfold change in titer is assessed only in comparable studies performed by the same method. [36]

Blood test control after treatment

In primary and secondary syphilis, clinical and serological monitoring is usually performed 6 and 12 months after treatment. The resulting titers are compared with the quantitative result recorded immediately before the start of therapy. [37]

In latent syphilis, quantitative nontreponemal testing is usually repeated after 6, 12, and 24 months. Longer follow-up is necessary because titers may decline more slowly in late or unknown duration infections. [38]

A sustained fourfold increase in titer, persisting for more than two weeks, may indicate reinfection or treatment failure. Particularly important are the simultaneous onset of symptoms of primary or secondary syphilis or a new risky sexual encounter. [39]

In some individuals, the titer after therapy decreases by less than 4-fold or remains at a low, stable level for a long time. This condition is sometimes called serofast, but it does not always indicate the persistence of live Treponema pallidum and requires individual evaluation. [40]

Treponemal tests are not used to assess the success of treatment because they remain positive in most patients. A repeated positive enzyme immunoassay after therapy does not prove that the antibiotic has failed and the infection continues to progress. [41]

Stage	Routine timing of serological testing	What are they comparing?
Primary syphilis	6 and 12 months	Nontreponemal titer with baseline value
Secondary syphilis	6 and 12 months	Titer and disappearance of symptoms
Early latent syphilis	According to the early infection protocol	Quantitative dynamics
Late latent syphilis	6, 12 and 24 months	Gradual decrease in titer
Possible re-infection	Immediately upon new risk or symptoms	Increase in titer and clinical picture
Pregnancy	More often according to obstetric protocol	Maternal titer and fetal examination results

The observation period may be shortened or extended in cases of pregnancy, immunodeficiency, neurological symptoms, and high risk of reinfection. [42]

False positive and false negative results

A nontreponemal test may be positive in the absence of syphilis. Biological false-positive reactions occur in approximately 0.2-0.8% of those tested and may be associated with human immunodeficiency virus, malaria, leprosy, autoimmune diseases, recent vaccination, and injection drug use. [43]

Pregnancy is also traditionally mentioned as a possible cause of false-positive reactions; however, modern laboratory data show that the frequency of false-positive nontreponemal tests in pregnant women is approximately comparable to that in the general population. Any reactive result during pregnancy should be confirmed by treponemal testing. [44]

A false negative result is possible at a very early stage, when the body has not yet produced sufficient antibodies. The sensitivity of non-treponemal tests for primary syphilis is significantly lower than for secondary syphilis, so a negative test with a characteristic ulcer does not rule out the disease. [45]

A rare cause of a false-negative nontreponemal test is the prozone phenomenon. At very high antibody concentrations, the normal formation of visible complexes is disrupted, causing undiluted serum to falsely appear negative; the laboratory can detect the problem by performing the test with additional dilutions. [46]

If the clinical picture strongly suggests primary or secondary syphilis and the nontreponemal result is negative, the physician may ask the laboratory to exclude the prozone phenomenon and order repeat serology or direct examination of material from the ulcer.[47]

Cause	What is the possible outcome?	What helps clarify the situation
Very early infection	Both tests are false negative.	Repeat after 2 weeks and examine the ulcer
The phenomenon of prozone	False negative nontreponemal test	Additional dilutions of the sample
Autoimmune disease	False positive nontreponemal test	Negative confirmatory treponemal test
Other infection	False-positive non-treponemal reaction	Repeat and confirm by another method
Pregnancy	Controversial or false positive result	Complete serological algorithm
Previously treated syphilis	Positive treponemal test	Medical history and current titer

If the result does not correspond to the symptoms, a repeat and confirmatory examination is necessary, rather than automatically excluding or confirming syphilis. [48]

Features of analysis during pregnancy, human immunodeficiency virus, and in newborns

Pregnant women should be tested for syphilis as early as possible, as prompt treatment significantly reduces the risk of transmitting the infection to the fetus. A positive screening result should be confirmed using a comprehensive algorithm, but testing and medical care should not be unnecessarily delayed. [49]

Treponemal and non-treponemal results in pregnancy are interpreted according to the same basic rules as in non-pregnant women. When using the reverse algorithm, a questionable result must be verified with a second treponemal test, since in populations with low infection prevalence, an isolated positive automated test may prove false. [50]

In most people living with human immunodeficiency virus (HIV), standard serologic testing remains sufficiently reliable for diagnosing syphilis and monitoring after therapy. Unusually high, low, or fluctuating titers are possible, but they also occur in people without HIV. [51]

To diagnose congenital syphilis, it is impossible to simply compare the positivity of treponemal tests of the mother and child, since maternal antibodies cross the placenta. A quantitative non-treponemal test in the infant is performed on its serum and compared with the maternal titer obtained during delivery. [52]

Umbilical cord blood is not recommended for non-treponemal testing because it may be contaminated with maternal blood and produce a false-positive result, and umbilical cord components can contribute to a false-negative reaction. A separate peripheral blood sample is collected for the child. [53]

Situation	Main feature
Pregnancy	The analysis is carried out early, controversial results are necessarily confirmed
New risk during pregnancy	A repeat examination is required regardless of the first screening.
Human immunodeficiency virus	Standardized tests are generally reliable.
Newborn	The titer is compared with the maternal value at birth
Umbilical cord blood	Not suitable for reliable non-treponemal testing
The mother tested positive.	An assessment of the treatment, titer and condition of the child is required

Pregnancy and the neonatal period require particularly careful interpretation, as an error may lead to congenital syphilis or unnecessary treatment.[54]

How to prepare and how blood is taken

No special preparation is usually required for serological testing for syphilis. You may eat and drink water unless other tests are scheduled at the same time that require a fasting period. [55]

Prescribed medications are usually not discontinued on their own. The physician should be informed of recently taken antibiotics, especially penicillins, doxycycline, ceftriaxone, and other drugs with activity against Treponema pallidum, as inadvertent treatment of another infection may alter symptoms and serologic dynamics. [56]

For the test, a healthcare professional draws a small amount of blood from a vein in the arm. The procedure takes several minutes and may involve a brief prick, slight bruising, or tenderness at the puncture site. [57]

Before testing, it's helpful to have information about your previous syphilis infection ready: test dates, titer values, medication name, number of doses, and documentation of completed treatment. Without this information, a positive treponemal test may be mistaken for a new infection. [58]

You should also provide the approximate date of the last possible exposure, describe any ulcers, rashes, enlarged lymph nodes, visual and hearing impairment, and neurological symptoms. This information helps the physician determine when to perform a repeat test and whether blood testing is sufficient. [59]

Preparation	Is it necessary?
Come on an empty stomach	Usually no
Drink water	Can
Stop medications on your own	No
Report recent antibiotic use	Yes
Bring old results and credits	Desirable
Name the date of possible contact	Yes
Report pregnancy	Necessarily
Tell us about a vision or hearing impairment	Necessarily

If glucose, lipid profile or other tests are prescribed on the same day, fasting rules are determined not by the syphilis test, but by additional tests. [60]

When a blood test alone is not enough

In fresh ulcers, serology may be negative, so material from the lesion is sometimes examined using dark-field microscopy or nucleic acid amplification. Direct detection of Treponema pallidum is particularly valuable in the early stages before antibodies appear. [61]

Molecular testing can be performed on genital, anal, or oral ulcer material if the laboratory has the appropriate methodology. A negative result does not always rule out syphilis, so it is compared with serology and the clinical picture. [62]

If signs of neurosyphilis are present, including cranial nerve damage, meningitis, stroke, altered mental status, or loss of vibration sensation, a blood test alone is insufficient. A lumbar puncture may be necessary to examine the cerebrospinal fluid. [63]

A positive CSF STD test in the absence of blood contamination is considered highly specific for neurosyphilis. However, a negative result does not completely rule out the disease, as the sensitivity of this method is limited. [64]

If vision is impaired, a person with a positive serology should undergo a full ophthalmological examination, and if hearing is impaired, an auditory examination should be performed. Isolated ocular or aural syphilis can occur without other obvious neurological manifestations. [65]

Clinical situation	Additional research
Fresh suspicious ulcer	Microscopy or molecular testing of the material
Negative blood with characteristic chancre	Repeat serology after 2 weeks
Stroke-like or meningeal symptoms	Cerebrospinal fluid analysis
Sudden loss of vision	Urgent ophthalmological examination
Hearing or balance impairment	Otological examination
Controversial serological results	Second treponemal test of a different type

The presence of dangerous eye, auditory, or neurological symptoms requires urgent medical evaluation rather than waiting for a routine blood test.[66]

Key points from experts

John R. Papp, PhD, a specialist at the U.S. Centers for Disease Control and Prevention and lead author of the 2024 syphilis laboratory guidelines, said his working group's main practice message is that the diagnosis of syphilis requires the combined use of treponemal and nontreponemal tests because neither test alone can reliably distinguish active from previously treated infection. [67]

Ina Park, MD, a professor at the University of California, San Francisco, and a medical adviser to the U.S. Centers for Disease Control and Prevention, is a co-author of the 2024 guidelines and emphasizes that laboratory results should be evaluated alongside clinical manifestations, previous treatment, and the likelihood of recent infection. [68]

Margaret Kingston, Consultant Genitourinary Physician, Fellow of the Royal College of Physicians and lead author of the 2024 UK Syphilis Guidelines. The guideline's practice statement is that a positive screening test should be confirmed with another treponemal test and a quantitative non-treponemal titre should be recorded on the day of treatment initiation.[69]

Edward Hook III, MD, is an expert in the prevention, diagnosis, and treatment of sexually transmitted infections at the University of Alabama at Birmingham. His research highlights the need for improved laboratory diagnostics, as the short clinical stages and subsequent asymptomatic course make syphilis particularly challenging to detect. [70]

The general expert opinion is that the laboratory provides a set of results, not a ready-made, independent diagnosis. Correct interpretation requires the stage of the disease, the time of possible exposure, previous titers, treatment information, and the risk of reinfection. [71]

Frequently asked questions

What is the name of the basic blood test for syphilis? Not one, but at least two complementary tests are used: a treponemal test and a quantitative non-treponemal test. The specific names depend on the laboratory's equipment and the algorithm used. [72]

Is it possible to use only the rapid plasma reagin test? An isolated reactive result does not confirm syphilis, as biological false-positive reactions are possible. It must be supplemented with a treponemal test. [73]

Is it possible to test only for treponemal antibodies? This test is suitable for screening, but if the result is positive, a quantitative non-treponemal test is required, and if the results differ, a second treponemal test is required. [74]

How long after exposure does a test become positive? The time frame varies: antibodies may not be detectable for the first few weeks, and reliable exclusion after a recent risk sometimes requires a repeat test up to 12 weeks after exposure. If an ulcer or rash develops, testing should be done immediately. [75]

Can a test be negative if a chancre is present? Yes. In the early stages, the sensitivity of serological tests is limited because antibodies have not yet been produced in sufficient quantities. [76]

When to repeat testing for a suspected ulcer? British guidelines recommend repeating serological testing after 2 weeks if the initial result and direct examination of the ulcer are negative, but suspicion remains. [77]

Do I need to fast for the test? No, special preparation is usually not required. Fasting is only necessary if other tests with corresponding requirements are scheduled at the same time. [78]

What does a positive treponemal test mean after treatment? In most people, it remains positive for life and does not indicate treatment failure. The dynamics of the quantitative non-treponemal titer are used for monitoring. [79]

What does a 1:32 result mean? This is the titer of a non-treponemal test: antibodies remain detectable after a 32-fold dilution of the serum. The value is not assessed in isolation, but rather in comparison with previous and subsequent results. [80]

What titer reduction is considered significant? A fourfold reduction is considered clinically significant, for example, from 1:32 to 1:8 or from 1:16 to 1:4. [81]

Why didn't the titer become negative after treatment? Nontreponemal antibodies can persist at a low, stable level for a long time. This doesn't always indicate an active infection, especially if treatment was complete and the titer had previously dropped significantly. [82]

Can syphilis produce a false-positive test? Yes. This is more common with non-treponemal tests, which can react to other infections, autoimmune diseases, vaccinations, pregnancy, and some other conditions. [83]

What is the prozone phenomenon? This is a rare situation in which an excessively high concentration of antibodies interferes with the normal reaction of a nontreponemal test, creating a false-negative result. To detect this, the laboratory tests diluted serum. [84]

Is it possible to determine when infection occurred based on a test? The exact day of infection cannot be determined based on titer or antibody positivity. The stage is determined based on symptoms, previous negative tests, contacts, and the dynamics of results. [85]

Does the test indicate that syphilis is completely cured? No single result provides such an answer. The doctor evaluates the disappearance of symptoms, the dynamics of the non-treponemal titer, and the absence of signs of reinfection. [86]

Should a sexual partner be tested? Yes. If syphilis is confirmed, the partner should seek medical attention for evaluation, testing, and, depending on the timing and nature of the exposure, prophylactic treatment. [87]

Is it possible to perform a rapid home test? The World Health Organization allows the use of rapid and self-administered tests as an additional way to expand access to testing, but a reactive result requires confirmation and medical evaluation. [88]

Is a lumbar puncture necessary for every positive test? No. CSF testing is performed primarily for neurological signs or other specific situations, and not for all people with positive serology. [89]

What should you do if you test positive during pregnancy? You should consult an obstetrician and a specialist in sexually transmitted infections as soon as possible. Early diagnosis and treatment reduce the risk of congenital syphilis. [90]

Conclusion

A blood test for syphilis is not a single test, but a diagnostic algorithm. Treponemal tests confirm exposure to Treponema pallidum, while quantitative non-treponemal tests help assess the activity of the infection and monitor the response to treatment. [91]

A negative result soon after exposure does not always rule out syphilis. If there is an ulcer, rash, known exposure, pregnancy, or neurological, visual, or auditory symptoms, testing should be performed immediately and then repeated if necessary. [92]

A positive result also cannot be interpreted independently. To make an accurate diagnosis, the doctor needs a combination of tests, a quantitative titer, information about previous treatment, the timing of possible infection, and the dynamics of previous tests. [93]