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.

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.

The IgM Immunodominant C6 test measures early antibodies against the conserved C6 peptide of VlsE, a key surface protein of Borrelia burgdorferi sensu lato. Because the IR6 region of VlsE is highly conserved across major Lyme-causing subspecies (B. burgdorferi sensu stricto, B. afzelii, B. garinii), C6-based assays serve as valuable pan-Borrelia markers in Lyme serology. IgM to C6 typically appears within 1–3 weeks of infection, making it especially useful for detecting recent exposure, particularly in patients with early localized symptoms, neurological manifestations, or evolving musculoskeletal involvement. While C6 ELISAs show strong sensitivity and specificity, IgM alone is not diagnostic—isolated IgM after 6–8 weeks or cross-reactivity with other pathogens (including Borrelia miyamotoi) can lead to nonspecific results. 

An equivocal IgM C6 result means antibody levels are near the cut-off, leaving interpretation uncertain; this may reflect very early infection, low-level reactivity, or a nonspecific immune response, so repeat or confirmatory testing is often required.

The IgM LFA Antigen + CK10 test measures two important parts of the immune system. The IgM portion looks for the body’s early-response antibodies, which usually appear soon after an infection begins, such as from a virus, bacteria, or parasite. Detecting IgM often suggests a recent or ongoing infection, while unusually persistent IgM levels may also point to chronic immune activity. The CK10 portion of the test checks for antibodies against cytokeratin 10, a protein found in skin and epithelial cells. Antibodies to CK10 can be a clue that the immune system is mistakenly targeting the body’s own tissues, as seen in certain autoimmune skin or inflammatory conditions. Together, these markers can help distinguish whether symptoms are more likely due to infection, autoimmunity, or both. 

If results are reported as equivocal, antibody levels are near the cut-off, meaning the test is uncertain; in these cases, repeat or confirmatory testing is often recommended.

IgM OspA + OspC

The IgM OspA + OspC test helps detect an early immune response to Borrelia burgdorferi, the bacteria that cause Lyme disease. It looks for IgM antibodies against two important surface proteins:

• OspC (Outer Surface Protein C): Typically produced within the first 2–3 weeks after infection, making it a strong marker for early Lyme disease.

• OspA (Outer Surface Protein A): More often linked with later or persistent infection, and sometimes associated with chronic or autoimmune-like Lyme symptoms.

By measuring IgM antibodies against both proteins, this test provides a broader view of where a person may be along the Lyme disease timeline.

Why It Matters

The IgM OspA + OspC test can be useful for people who have:

• Early Lyme symptoms such as rash, fever, fatigue, or muscle pain

• Neurological signs including facial palsy or nerve discomfort

• Joint pain or swelling that appears weeks to months after infection

• A history of tick exposure in areas where Lyme disease is common

Things to Keep in Mind

IgM antibodies are most reliable in the early weeks of infection. On their own, they cannot confirm Lyme disease. False positives are possible, which is why doctors often order additional testing (such as IgG antibodies, VlsE/C6 peptide, or multi-antigen panels) to confirm results.

Patient Takeaway

A positive IgM OspA + OspC test suggests that your immune system is reacting to Borrelia and may indicate a recent or active infection. However, your healthcare provider will always consider your symptoms, exposure history, and other test results before making a diagnosis.

If your result is reported as equivocal (borderline), it means the antibody level is close to the cutoff and not clearly positive or negative. In this case, repeat testing or confirmatory panels are often recommended to clarify the result.

The IgM OspE test detects early antibodies against Outer Surface Protein E (OspE) of Borrelia burgdorferi, the bacterium responsible for Lyme disease. OspE belongs to the Erp (OspE-related proteins) family, which helps Borrelia survive in the human bloodstream by binding to factor H, a host protein that protects the bacteria from complement-mediated killing.

The IgM Variable Major Protein E (VmpE) test detects early antibodies against a surface protein that Borrelia burgdorferi—the bacteria responsible for Lyme disease—uses to survive through antigenic variation. VmpE can repeatedly alter its structure, enabling Borrelia to evade immune detection and, in some cases, contribute to persistent or relapsing infection.

IgM antibodies to VmpE usually appear within the first 1–3 weeks after infection, making this test valuable for identifying recent exposure to Lyme disease. In some cases, IgM reactivity may also remain detectable in ongoing immune activation, offering insights into possible bacterial persistence.

Clinically, IgM VmpE provides complementary information to markers such as OspC and VlsE, helping clinicians assess both early immune recognition and potential long-term Borrelia activity.

As with all IgM-based assays, results must be interpreted alongside patient history, symptoms, and additional confirmatory markers.

An equivocal IgM VmpE result means antibody levels are near the test cut-off, leaving the finding uncertain. This may reflect very early infection, a nonspecific immune response, or cross-reactivity. In such cases, repeat or follow-up testing is usually recommended to clarify the result.

IL-1 beta refers to Interleukin-1 beta. Interleukin-1 beta is one of the cytokines assessed in the CytoDx Cytokine Response Profile offered by Diagnostic Solutions Laboratory. Cytokines are critical mediators of immune responses, and their imbalances have been linked to chronic inflammation and autoimmune diseases.