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Lyme disease in dogs: the 4Dx test, C6 and kidney checks

A positive Lyme result on the yearly 4Dx test worries many owners. Yet most dogs that test positive never become ill. Here is what the C6 antibody test really tells you, which signs suggest true Lyme disease, and why vets check the urine of every positive dog.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Lyme disease is caused by Borrelia burgdorferi, carried by Ixodes ticks. A positive C6 antibody test (for example on the SNAP 4Dx) shows exposure, not disease: most positive dogs stay healthy. True Lyme disease usually shows as sudden lameness with fever, and improves within days of antibiotics. The rare but serious form is Lyme nephritis, a kidney disease that leaks protein, seen in under 2% of positive dogs, more often in Labrador and Golden Retrievers. That is why every positive dog should have its urine protein (UPC) checked.

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A positive Lyme test: exposure, not illness

The ACVIM consensus is clear: most dogs with antibodies to Borrelia show no signs of illness, both in experiments with tick exposure and in the field [1]. The European ESCCAP guideline adds that most infected dogs stay subclinical, and estimates that fewer than 5% of dogs suspected of Lyme disease actually have it [2].

Antibodies to the C6 peptide, measured by the SNAP 4Dx and 4Dx Plus, mean natural exposure to the bacterium [1]. Lyme vaccines do not make a dog C6-positive: in a study of dogs given 4 different vaccines, none became positive on the C6 tests [4]. A positive result is not proof that Borrelia causes a sign, and it does not predict future illness [1].

For the other infections on the same test, see the overview of tick-borne diseases in dogs, and the detailed pages on anaplasmosis and ehrlichiosis.

Signs of Lyme disease in dogs

  • Sudden lameness in one or more legs, with swollen joints: the classic picture, usually in young, often large, active outdoor dogs [1].
  • Fever, lethargy and mildly enlarged lymph nodes near the affected leg [1].
  • Delayed onset: in experimentally infected dogs, signs appeared 2 to 5 months after the tick bite, and young puppies became ill more easily than older dogs [3].
  • Rapid response to antibiotics, usually within 1 to 2 days, if the lameness is really due to Lyme disease [1].
  • Not typical in dogs: the skin, nerve and heart forms seen in people are rare and poorly documented in dogs [1].

Other tick infections can cause the same signs, so vets also look at the platelets and the rest of the blood count [1].

The Lyme tests and what they show

TestWhat it measuresWhat it tells you
SNAP 4Dx / 4Dx PlusAntibodies to C6 (yes/no)Natural exposure; not affected by vaccination. Recommended yearly in or near risk areas of North America [1, 4].
Quantitative C6 (Quant C6)Amount of C6 antibodyNot a screening test; a high value does not predict illness. Used by some vets as a baseline before treatment [1].
Lyme MultiplexAntibodies to OspA, OspC and OspFOspA usually reflects vaccination. OspC rises 2–3 weeks after exposure and fades in 3–5 months; OspF rises after 6–8 weeks and stays high in untreated carriers [1].
Urine protein:creatinine ratio (UPC)Protein lost in the urineRecommended for every positive dog, to detect Lyme nephritis early [1, 7].
Blood count and chemistryPlatelets, kidney values, albuminLooks for co-infections and kidney disease linked to tick exposure [1].

Antibodies usually appear 3 to 5 weeks after infection, so a very recent bite can still test negative [2]. The bacterium itself is rarely found in blood, urine or joint fluid, which is why antibody tests are used [2].

Lyme nephritis: the kidney form

Lyme nephritis is a kidney inflammation caused by immune complexes. It makes the kidneys leak protein (a protein-losing nephropathy). It is seen in fewer than 1–2% of positive dogs, at an average age of 5 to 6 years, and only 9–28% of affected dogs had lameness before [7]. Labrador and Golden Retrievers are predisposed: in a series of 49 dogs, they were 6.4 and 4.9 times more likely to develop it [6]. See the breed pages: Labrador Retriever and Golden Retriever.

Compared with other protein-losing kidney diseases, C6-positive dogs more often had low platelets, anemia, high kidney values and high phosphorus, with blood, glucose and white cells in the urine despite a negative culture [8]. There is no stain that proves Borrelia is the cause: the diagnosis rests on a positive dog with protein loss and no other cause found [1]. Read more on kidney disease in dogs.

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
UPC Urine protein:creatinine ratio2.4–< 0.2H
  1. Abbreviation UPC or UP/C: protein in the urine divided by urine creatinine, on a single sample.
  2. Result 2.4 in this illustrative line, from a C6-positive dog: clearly above normal.
  3. Unit A ratio, so it has no unit.
  4. Laboratory interval IRIS calls a dog non-proteinuric below 0.2, borderline from 0.2 to 0.5 and proteinuric above 0.5, ideally on two samples at least 2 weeks apart [9].
  5. Flag H: above the interval. In a Lyme-positive dog, the vet first rules out urine infection, bleeding and other causes. See protein in urine.

Follow-up and retesting

  • Healthy positive dogs: most ACVIM panelists (4 of 6) do not routinely treat them, but recommend checking urine protein at least 2 to 3 times a year [1].
  • The yes/no test can stay positive for a long time after treatment, so it is not used to judge success [1]. In experiments, antibody levels stayed high for 17 months [3].
  • Quantitative C6 before and 3–6 months after treatment was recommended by 4 of 6 panelists, to confirm a fall and set a new baseline; a later rise may mean re-exposure or relapse [1].
  • The fall depends on the starting level: in 53 treated healthy dogs, C6 dropped clearly at 6 and 12 months when it started moderate to high, and changed little when it started low [5].

Related articles

Tick-borne diseases in dogs

Lyme, Anaplasma and Ehrlichia on the 4Dx.

Read the article

En français : la maladie de Lyme du chien.

Questions to ask your veterinarian

  1. Is my dog positive for C6 only, or also for Anaplasma or Ehrlichia?
  2. Should we check the urine protein (UPC) now, and how often after that?
  3. Are the platelets, kidney values and albumin normal?
  4. Would a quantitative C6 test change anything for my dog?
  5. Which tick prevention do you recommend, and is the Lyme vaccine useful where we live?
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Frequently asked questions

Can a dog test positive for Lyme and not be sick?

Yes, and it is the most common situation. Most dogs with Lyme antibodies never show signs; the test shows exposure to infected ticks, not disease [1, 2].

What happens if Lyme disease is left untreated in dogs?

In experiments, lameness episodes were self-limiting and dogs recovered, but the bacterium persisted for at least a year with mild joint inflammation [1, 3]. The rare kidney form is the serious one: in a series of 49 dogs it progressed rapidly and was fatal [6].

How long does a dog stay positive for Lyme?

Often a long time. In experimentally infected dogs, antibodies stayed high for 17 months, and the yes/no test may stay positive long after treatment [1, 3].

Does the Lyme vaccine make the 4Dx test positive?

No. The C6 antigen is not in the vaccines; vaccinated dogs tested negative on the C6 tests [1, 4].

Can I catch Lyme disease from my dog?

Not directly. Dogs are not a reservoir for Borrelia, but ticks taken off them may carry it. A positive dog shows that infected ticks live in the area [2].

Sources

  1. Littman MP et al. ACVIM consensus update on Lyme borreliosis in dogs and cats. J Vet Intern Med. 2018;32(3):887-903. doi.org/10.1111/jvim.15085
  2. ESCCAP. Guideline 05: Control of vector-borne diseases in dogs and cats, 5th edition, 2024. esccap.org/guidelines/gl5
  3. Appel MJ et al. Experimental Lyme disease in dogs produces arthritis and persistent infection. J Infect Dis. 1993;167(3):651-664. doi.org/10.1093/infdis/167.3.651
  4. Stillman BA et al. Borrelia burgdorferi antibody test results in dogs administered 4 different vaccines. Top Companion Anim Med. 2019;37:100358. doi.org/10.1016/j.tcam.2019.100358
  5. Levy SA et al. Quantitative measurement of C6 antibody following antibiotic treatment of Borrelia burgdorferi antibody-positive nonclinical dogs. Clin Vaccine Immunol. 2008;15(1):115-119. doi.org/10.1128/CVI.00340-07
  6. Dambach DM et al. Morphologic, immunohistochemical, and ultrastructural characterization of a distinctive renal lesion in dogs putatively associated with Borrelia burgdorferi infection: 49 cases (1987-1992). Vet Pathol. 1997;34(2):85-96. doi.org/10.1177/030098589703400201
  7. Littman MP. Lyme nephritis. J Vet Emerg Crit Care. 2013;23(2):163-173. doi.org/10.1111/vec.12026
  8. Borys MA et al. Differences in clinicopathologic variables between Borrelia C6 antigen seroreactive and Borrelia C6 seronegative glomerulopathy in dogs. J Vet Intern Med. 2019;33(5):2096-2104. doi.org/10.1111/jvim.15586
  9. International Renal Interest Society (IRIS). IRIS Staging of CKD, modified 2026. iris-kidney.com/s/IRIS_staging_guidelines-2026.pdf

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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