Skip to content
How It Works
Explore
Resources Ask a Question
Who It's For
Patients
Decode results, prep for appointments, weigh options.
Caregivers & advocates
Carry the research load for someone you love.
Providers & clinicians
Resources for patients in your practice.
Log In Ask a Question
PubMed This is a summary of 17 peer-reviewed journal articles Updated
Infectious Disease

Diagnosis & Understanding Tests

At a Glance

Cat-scratch disease is primarily diagnosed using blood tests that check for IgG and IgM antibodies. Testing too early can cause a false negative, requiring a repeat test in 2 to 3 weeks. A PCR test on lymph node fluid can also detect the bacteria's DNA if blood tests are inconclusive.

Diagnosing Cat-scratch disease (CSD) is often a process of combining “puzzle pieces” from your medical history, physical exams, and laboratory data. Because the body takes time to respond to the Bartonella henselae bacteria, a single negative test result does not always mean the infection isn’t there [1][2].

Understanding Blood Tests (Serology)

The most common way to check for CSD is through serology, which looks for antibodies (proteins the immune system makes to fight the bacteria) in the blood [3].

  • IgM Antibodies: These are the “first responders.” They usually appear early in an infection but may only be detectable for a short window [4]. IgM tests for CSD can have low sensitivity (about 28% to 54%), meaning they often miss the infection even when it is present [5][6].
  • IgG Antibodies: These appear slightly later and stay in the system longer. A high level (titer) of IgG often suggests a current or recent infection [7].
  • The “Window Period”: If a blood test is done too early—before the body has made enough antibodies—it may come back as a false negative [2][8]. If symptoms persist, doctors often recommend a repeat test 2 to 3 weeks later to look for a rise in antibody levels [1][9].

Molecular Testing (PCR)

PCR (Polymerase Chain Reaction) is a highly specific test that looks for the actual DNA of the bacteria rather than the body’s immune response [10][11].

  • When it’s used: PCR is especially helpful in atypical cases or when blood tests are inconclusive [12][13].
  • The Sample Matters: PCR is much more accurate when performed on a sample of pus or tissue from the infected lymph node rather than just a blood sample [14].

Completeness Checklist for Your Results

When reviewing your labs, ensure you have answers to the following to get the clearest picture:

  1. Timing: Was the test done at least 1-2 weeks after symptoms started? [2]
  2. Antibody Types: Did the panel include both IgG and IgM? [4]
  3. Consistency: Do the results match the findings on imaging? [15][16]
  4. Follow-up Plan: If the test was negative but suspicion is high, is a repeat titer scheduled for 2-3 weeks from now? [1]

By combining these different tools, your medical team can build a strong case for diagnosis, even if the bacteria themselves are difficult to find [17].

Common questions in this guide

Why might my cat-scratch disease blood test be negative if I have symptoms?
If a blood test is done too early, before your body has produced enough antibodies, it can result in a false negative. This is known as the window period. Doctors often recommend repeating the test two to three weeks later to check for rising antibody levels.
What is the difference between IgM and IgG antibodies in a CSD test?
IgM antibodies are the first responders that appear early in the infection, though they can sometimes be difficult to detect. IgG antibodies appear slightly later, stay in your system longer, and high levels usually indicate a current or recent infection.
What is a PCR test for cat-scratch disease?
A PCR test looks for the actual DNA of the Bartonella henselae bacteria rather than your body's immune response to it. It is highly specific and is most accurate when performed on a sample of fluid or tissue taken directly from an infected lymph node.
When is a PCR test used instead of a blood test for CSD?
Blood tests are usually the first step to check for an immune response to the bacteria. If those results are unclear or if you have an atypical case, your doctor may recommend a PCR test using a sample from a swollen lymph node to confirm the diagnosis.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Was this blood test for IgG, IgM, or both, and what do those results tell us about the timing of the infection?
  2. 2.Since the initial antibody test was negative but symptoms are still present, should we wait two weeks and repeat the test to check for seroconversion?
  3. 3.Could this be a false negative due to testing too early in the course of the illness?
  4. 4.If we decide to do a lymph node aspiration, can we send that sample for a PCR test instead of just a culture?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (17)
  1. 1

    Bartonella neuroretinitis (cat-scratch disease).

    Yap SM, Saeed M, Logan P, Healy DG

    Practical neurology 2020; (20(6)):505-506 doi:10.1136/practneurol-2020-002586.

    PMID: 32546517
  2. 2

    Uncovering the truth about cat-scratch disease.

    Puspitasari Y, Khairullah AR, Raharjo HM, et al.

    Open veterinary journal 2025; (15(5)):1895-1906 doi:10.5455/OVJ.2025.v15.i5.5.

    PMID: 40557109
  3. 3

    Analytical and clinical evaluation of new automated chemiluminescent immunoassays for the detection of IgG and IgM anti-Bartonella henselae antibodies.

    Bayart JL, Gusbin C, Lardinois B, et al.

    Diagnostic microbiology and infectious disease 2020; (98(4)):115203 doi:10.1016/j.diagmicrobio.2020.115203.

    PMID: 33032158
  4. 4

    Cat scratch disease in children with nocturnal fever: A case report.

    Yin QL, Liu YQ, Zhang HM, et al.

    World journal of clinical cases 2024; (12(35)):6840-6847 doi:10.12998/wjcc.v12.i35.6840.

    PMID: 39687640
  5. 5

    Utility of Bartonella henselae IgM Western Blot Bands for Serodiagnosis of Cat Scratch Disease.

    Otsuyama KI, Tsuneoka H, Yoshidomi H, et al.

    Journal of clinical microbiology 2018; (56(1)) doi:10.1128/JCM.01322-17.

    PMID: 29093103
  6. 6

    Bartonella henselae infection in diverse clinical conditions in a tertiary care hospital in north India.

    Chaudhry R, Kokkayil P, Ghosh A, et al.

    The Indian journal of medical research 2018; (147(2)):189-194 doi:10.4103/ijmr.IJMR_1932_16.

    PMID: 29806608
  7. 7

    Real-life assessment of the VirClia® IgG chemiluminescence test for the diagnosis of Bartonella henselae infection.

    Pollani C, Floch P, Grouteau G, et al.

    Diagnostic microbiology and infectious disease 2026; (114(2)):117187 doi:10.1016/j.diagmicrobio.2025.117187.

    PMID: 41242076
  8. 8

    Cat scratch disease: Pediatric case series for varying presentations of Bartonella henselae.

    Lin S, Saccoccio FM

    IDCases 2023; (33()):e01875 doi:10.1016/j.idcr.2023.e01875.

    PMID: 37609448
  9. 9

    A 31-year-old man with bilateral blurry vision and floaters.

    Abazari A, Kaplowitz K, Sibony P

    Digital journal of ophthalmology : DJO 2015; (21(2)):1-11 doi:10.5693/djo.03.2014.08.003.

    PMID: 27330461
  10. 10

    Fever, bone pain and erectile dysfunction. Where is the cat?

    Trefois Q, Marot JC, Yildiz H, Wieers G

    BMJ case reports 2017; (2017()) doi:10.1136/bcr-2017-221397.

    PMID: 28899872
  11. 11

    [Bone involvement in cat scratch disease].

    Razafindrazaka H, Redl S, Aouchiche F, et al.

    La Revue de medecine interne 2021; (42(12)):875-880 doi:10.1016/j.revmed.2021.06.010.

    PMID: 34215457
  12. 12

    Cat Scratch Disease of the Breast/Axilla: Recognition of a Rare Disease and Approaches for Differential Diagnosis.

    Wang J, Yan M, Bomeisl P, et al.

    International journal of surgical pathology 2024; (32(7)):1379-1388 doi:10.1177/10668969241228296.

    PMID: 38327174
  13. 13

    Bartonella henselae DNA in Seronegative Patients with Cat-Scratch Disease.

    Yanagihara M, Tsuneoka H, Tanimoto A, et al.

    Emerging infectious diseases 2018; (24(5)):924-925 doi:10.3201/eid2405.152033.

    PMID: 29664374
  14. 14

    Molecular Diagnosis of Cat Scratch Disease: a 25-Year Retrospective Comparative Analysis of Various Clinical Specimens and Different PCR Assays.

    Goaz S, Rasis M, Binsky Ehrenreich I, et al.

    Microbiology spectrum 2022; (10(2)):e0259621 doi:10.1128/spectrum.02596-21.

    PMID: 35262411
  15. 15

    Suspected Hepatosplenic Cat Scratch Disease with No Major Symptoms and Negative Serology: A Case Report.

    Osawa H, Shibutani K, Mori N

    The American journal of case reports 2025; (26()):e949495 doi:10.12659/AJCR.949495.

    PMID: 41160532
  16. 16

    Case Report: Co-infection with cat-scratch disease and infectious mononucleosis: a rare clinical entity.

    Huang W, Yuan J, He H

    Frontiers in pediatrics 2025; (13()):1660853 doi:10.3389/fped.2025.1660853.

    PMID: 41378194
  17. 17

    Serological and molecular detection of Bartonella henselae in specimens from patients with suspected cat scratch disease in Italy: A comparative study.

    Allizond V, Costa C, Sidoti F, et al.

    PloS one 2019; (14(2)):e0211945 doi:10.1371/journal.pone.0211945.

    PMID: 30735549

This page explains diagnostic tests for cat-scratch disease for educational purposes only. Always consult your healthcare provider to interpret your specific laboratory results and determine the best follow-up plan.

Get notified when new evidence is published on Cat-scratch disease.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.