IgG (Immunoglobulin G) is a vital part of your immune defense system. Abnormal levels—either too high or too low—can be a sign of chronic infection, autoimmune activity, immune deficiency, or other systemic conditions. Whether you're experiencing frequent infections or unexplained inflammation, this test offers critical insight into how your immune system is functioning and what steps may be needed next.

IgG, Quant, CSF stands for Immunoglobulin G, Quantitative, Cerebrospinal Fluid. This test measures the concentration of IgG, a type of antibody, in your cerebrospinal fluid (CSF)—the clear fluid that surrounds your brain and spinal cord.

What is IgG?

Immunoglobulin G (IgG) is the most abundant antibody in the body. It plays a critical role in immune defense by identifying and neutralizing viruses, bacteria, and other foreign substances. IgG is normally found in the blood but can also be present in small amounts in the CSF.

IgG is a combination of four slightly different types of IgG called IgG subclasses: IgG1, IgG2, IgG3 and IgG4. When one or more of these subclasses is persistently low and total IgG is normal, a subclass deficiency is present.

IgG is a combination of four slightly different types of IgG called IgG subclasses: IgG1, IgG2, IgG3 and IgG4. When one or more of these subclasses is persistently low and total IgG is normal, a subclass deficiency is present.

IgG is a combination of four slightly different types of IgG called IgG subclasses: IgG1, IgG2, IgG3 and IgG4. When one or more of these subclasses is persistently low and total IgG is normal, a subclass deficiency is present.

IgG is a combination of four slightly different types of IgG called IgG subclasses: IgG1, IgG2, IgG3 and IgG4. When one or more of these subclasses is persistently low and total IgG is normal, a subclass deficiency is present.

The IgG Synthesis Rate (CSF) measures how much immunoglobulin G (IgG) is being actively produced within the central nervous system (CNS)—specifically the brain and spinal cord. It helps determine whether the immune system is generating antibodies inside the CNS, which can signal inflammation, infection, or autoimmune activity affecting the brain or spinal cord.

Why it matters:
While some IgG naturally crosses from the blood into the cerebrospinal fluid (CSF), an elevated IgG synthesis rate means the immune system is producing extra IgG locally within the CNS. This is a hallmark of conditions like multiple sclerosis (MS), chronic CNS infections, or autoimmune neuroinflammatory diseases.

The IgG/Alb Ratio, CSF helps distinguish whether elevated IgG in the cerebrospinal fluid is due to local immune activity or simply leakage through a damaged blood-brain barrier. A high ratio often points to neurological conditions like multiple sclerosis or chronic CNS infections. A normal or low ratio suggests stable immune activity and barrier integrity.

IgM B. afzelii measures early antibodies against Borrelia afzelii, a major cause of Lyme disease in Europe and Asia. Unlike B. burgdorferi sensu stricto, which dominates in North America, B. afzelii is strongly linked to skin-related forms of Lyme borreliosis, including erythema migrans and acrodermatitis chronica atrophicans (ACA). IgM antibodies typically appear within the first weeks of infection, making this marker useful for detecting recent or early exposure, especially in patients with skin or joint symptoms after tick bites. Because low-level or isolated IgM responses can reflect cross-reactivity or false positives, results should always be interpreted with other Borrelia markers, clinical history, and follow-up testing.

If your result is Equivocal or Borderline (close to the cut-off):

What it means: Borderline levels of IgM antibodies were detected against Borrelia afzelii. This may represent an early or low-level immune response, or it may reflect non-specific reactivity rather than true Lyme infection. Results in this range require careful interpretation, particularly if you have Lyme-like symptoms or known tick exposure.

Next steps: Your doctor may recommend repeat testing after a few weeks, reviewing other Lyme antibody markers (including B. burgdorferi and B. garinii), or confirming with an immunoblot. Clinical history and symptoms are essential to determine whether this finding represents Lyme disease.

Next Steps for an Equivocal Result

• Repeat testing: Because IgM antibodies may rise in the early weeks after infection, repeating the test in 2–4 weeks can help clarify whether the immune response is increasing (suggesting infection) or fading (suggesting no infection).

• Additional Lyme tests: Your doctor may order IgG antibody testing, immunoblots, or a broader Lyme panel (including other Borrelia subspecies and Osp proteins) to confirm the result.

• Consider co-infections: If exposure risk is high, testing for tick-borne co-infections (e.g., Babesia, Bartonella, Ehrlichia) may also be recommended.

• Clinical evaluation: Symptoms and history of tick exposure are critical. Even borderline results can be significant if you have classic Lyme signs such as erythema migrans, joint pain, neurological changes, or unexplained fatigue.

• Ongoing monitoring: If symptoms persist but results remain unclear, your provider may recommend ongoing monitoring and possibly other diagnostic methods such as PCR.

The IgM B. burgdorferi sensu stricto test helps detect early Lyme disease by measuring IgM antibodies, which the body produces soon after a tick bite. A positive result may point to a recent infection, but it isn’t always proof of active disease because false positives and lingering IgM can occur. Doctors use this test along with symptoms (such as rash, fever, tiredness, joint or nerve problems) and exposure history to make an accurate diagnosis. Finding Lyme disease early is important, since timely treatment can prevent serious complications affecting the joints, nervous system, or heart.

The IgM B. burgdorferi Antigen (AG) test measures early antibodies against a broad set of Borrelia burgdorferi proteins, making it a sensitive marker for detecting early Lyme disease. IgM antibodies typically appear within 1–2 weeks after a tick bite and peak in the first month, so a positive result may indicate a recent or active infection. However, IgM alone is not diagnostic: results can persist after treatment or arise from cross-reactions with other infections or autoimmune conditions. Therefore, this marker is most valuable when interpreted with symptoms, exposure history, IgG results, and confirmatory tests. As part of a comprehensive Lyme serology panel, the IgM AG test supports early recognition and management of Lyme disease, helping to prevent progression to later complications affecting joints, the nervous system, or the heart.

An equivocal result means your IgM antibody level is right at the borderline — not clearly negative, but not strongly positive either. This does not confirm Lyme disease. Sometimes this happens if the test is done very soon after a tick bite, before antibodies fully develop, or because of background signals in the immune system. Your doctor may suggest repeating the test after a few weeks, checking for other antibodies, and reviewing your symptoms and history before making any diagnosis.

The IgM B. garinii test detects early antibodies against Borrelia garinii, a subspecies within the Borrelia burgdorferi sensu lato complex that is especially common in Europe and Asia and strongly associated with neurological forms of Lyme disease (neuroborreliosis). IgM antibodies typically appear 1–3 weeks after infection, making this marker useful for identifying recent immune responses in patients with early neurological symptoms such as meningitis, facial nerve palsy, radiculoneuritis, or cognitive issues. While a positive result may support an early diagnosis, interpretation depends on clinical context, timing, and geography, since false positives and persistent IgM without IgG conversion can occur. The test is most informative when combined with other Lyme markers (e.g., B. burgdorferi sensu stricto, B. afzelii, or Osp proteins), helping clinicians recognize neurological Lyme disease earlier and guide appropriate management.

An equivocal result means the test is in the borderline range — not clearly negative, but not fully positive either. This can happen if testing is done very early after a tick bite, before antibodies have built up, or if the signal comes from the immune system reacting to something else. On its own, this result does not confirm or rule out Lyme disease. Your doctor may recommend repeating the test, checking other Lyme markers, and reviewing your symptoms and travel or exposure history to get a clearer answer.

The IgM B. miyamotoi test detects early antibodies against Borrelia miyamotoi, a relapsing fever–type spirochete transmitted by the same Ixodes ticks that spread Lyme disease. Unlike classical Lyme borreliosis, B. miyamotoi causes Borrelia miyamotoi disease (BMD), which typically presents with acute, flu-like illness and recurring episodes of fever, and in some cases, neurological complications such as meningoencephalitis, particularly in immunocompromised patients. Importantly, BMD rarely produces the bull’s-eye rash seen in Lyme disease, making antibody testing critical for recognition. A positive IgM result generally indicates recent or active infection, but interpretation should take clinical symptoms, geographic exposure, and confirmatory testing into account, since cross-reactivity with Lyme Borrelia is possible. 

An equivocal result means the antibody level is close to the test’s cut-off, and may reflect very early infection, low-level cross-reactivity, or a nonspecific finding; in such cases, repeat testing or additional confirmatory assays are often needed for clarity.

The IgM Babesia test measures early antibodies against Babesia species, tick-borne protozoan parasites that invade red blood cells and can cause babesiosis, a malaria-like illness. In North America, Babesia microti is most common, while B. divergens and B. venatorum predominate in Europe, often leading to more severe disease. IgM antibodies typically appear within 1–2 weeks of infection, making this marker useful for identifying recent or acute cases before IgG antibodies or confirmatory findings emerge. Clinically, babesiosis can range from flu-like symptoms (fever, chills, sweats, fatigue) to hemolytic anemia, splenomegaly, and multi-organ complications, especially in elderly or immunocompromised patients, or those without a spleen. Because the same ticks can also transmit Lyme disease (Borrelia) and Anaplasma, co-infections are common and can complicate the illness. 

An equivocal IgM Babesia result means antibody levels are near the cut-off, making the finding uncertain; this may reflect very early infection, low-level reactivity, or nonspecific response, and repeat or confirmatory testing is often needed for clarification.

The IgM Bartonella test detects early antibodies against Bartonella species, a group of bacteria transmitted by ticks, fleas, lice, or scratches from infected animals (especially cats). The most common human pathogens are Bartonella henselae and Bartonella quintana, which can cause cat scratch disease, trench fever, or tick-borne bartonellosis. In some cases, Bartonella infections may contribute to chronic fatigue, neurological issues, or joint pain, especially when co-infections with Lyme disease or Babesia are present.

IgM Cytomegalovirus (CMV) measures the level of IgM antibodies, which are the body’s first line of defense when encountering a virus. These antibodies typically appear during a new CMV infection or during viral reactivation. Because CMV is a common virus—often acquired in childhood—IgM testing helps determine whether your immune system is responding to a recent or ongoing infection.

CMV IgM is often used together with CMV IgG, clinical symptoms, or PCR testing to clarify whether the infection is new, reactivating, or clinically significant.

What It Means When Your IgM CMV Result Is Within the Reference Range (Negative)

A negative or normal IgM CMV result means there is no evidence of a recent or active CMV infection at the time of testing.

When IgM is within the reference range:

• Your immune system is not producing new CMV-specific IgM antibodies.

• There is no laboratory indication of a current or very recent infection.

• Viral reactivation is unlikely based on this marker alone.

• If you have CMV IgG antibodies, they reflect past exposure only, not new illness.

A negative IgM result is reassuring and is the most common finding in healthy individuals.

IgM EB Nuclear Antigen (EBNA IgM) measures early antibodies directed against the Epstein–Barr Virus (EBV) Nuclear Antigen. Unlike other EBV markers, such as VCA IgM, EBNA IgM is not commonly produced and is generally not a standard marker of acute infection. When it does appear, it may indicate an early-phase immune response, but it is less specific and less commonly used in clinical decision-making.

Because EBNA proteins are expressed later in the EBV life cycle, IgM antibodies to EBNA are rarely detected during typical EBV infections. For this reason, clinicians rely more heavily on VCA IgM, VCA IgG, EBNA IgG, and Early Antigen when evaluating EBV activity.

EBNA IgM can sometimes be included in extended EBV panels to help rule out atypical or early immune responses.

What It Means When Your EBNA IgM Result Is Within the Reference Range (Negative)

A negative or normal EBNA IgM result means there is no evidence of a recent or acute immune response to the EBV Nuclear Antigen. In practical terms, this indicates:

• Your immune system is not producing early-phase EBNA-specific IgM antibodies.

• There is no laboratory support for an active or newly developing EBV infection based on this marker.

• This result is consistent with the vast majority of healthy individuals, as EBNA IgM is typically not elevated even during routine EBV infections.

When EBNA IgM is within the reference range:

• EBV infection is unlikely to be recent.

• If other EBV markers (VCA IgM, EA IgG) are also negative, it supports the conclusion that EBV is not active.

• Past infection—if present—would be reflected in EBNA IgG, not in this marker.

A negative EBNA IgM result is expected and reassuring, especially in the absence of symptoms suggestive of acute mononucleosis.

The IgM Ehrlichia test detects early antibodies to Ehrlichia species, tick-borne bacteria that invade white blood cells and cause ehrlichiosis, most often due to E. chaffeensis (human monocytic ehrlichiosis) or E. ewingii. IgM antibodies usually appear within 1–2 weeks of illness, making this marker useful for identifying recent or acute infection, particularly in patients presenting with fever, severe headache, fatigue, muscle aches, gastrointestinal upset, or neurological changes. Laboratory findings commonly include low white blood cells, low platelets, and elevated liver enzymes. Because ehrlichiosis can progress rapidly to severe complications in older adults, immunocompromised patients, or those with delayed treatment, timely recognition and empiric doxycycline therapy are critical. However, IgM alone is not definitive since early levels can be low and false positives may occur. 

An equivocal IgM Ehrlichia result means the antibody level is near the cut-off, leaving the test uncertain; this may reflect very early infection, a nonspecific immune response, or cross-reactivity, and repeat or confirmatory testing (PCR or IgG serology) is often needed.

IgM Epstein–Barr Virus Viral Capsid Antigen (EBV VCA IgM) measures early antibodies produced by the immune system during a new or recent Epstein–Barr virus infection. EBV is a common virus best known for causing infectious mononucleosis (“mono”), especially in adolescents and young adults.

VCA IgM antibodies are typically:

• Detectable during the acute phase of infection

• Present for only a short period (usually several weeks)

• Used to help identify whether symptoms—such as fatigue, swollen lymph nodes, sore throat, or fever—are related to a current EBV infection

Because IgM rises quickly and declines relatively fast, it is a key marker for determining if EBV infection is occurring now or very recently.

What It Means When Your IgM EBV VCA Result Is Within the Reference Range (Negative)

A negative or normal IgM EBV VCA result means there is no evidence of a recent or active Epstein–Barr virus infection at the time of testing.

When this marker is within the reference range:

• Your immune system is not producing early, active-phase EBV antibodies.

• There is no laboratory indication of a current mono-like infection.

• Any past exposure you may have had is not recent—and would instead be reflected in EBV IgG markers, not IgM.

• This result is reassuring and is the most common finding in individuals without active symptoms.

A negative IgM result is especially helpful when interpreting the rest of the EBV panel; it supports the conclusion that EBV is not driving current symptoms.

If symptoms persist, clinicians may look at additional markers—such as EBV EBNA IgG, EBV VCA IgG, or Early Antigen (EA)—to build a more complete picture.