How do you interpret/use Brucella blood sampling results?

RE: How do you interpret/use Brucella blood sampling results?

Rob Loxley — Thu, 07 Dec 2023 08:33:46 GMT

[quote userid="8958" url="~/f/clinical-questions/30838/how-do-you-interpret-use-brucella-blood-sampling-results"]As it is so rare and in less than 1% of the population, you cannot trust a positive result. Something akin to 50% are wrong which could be pretty devastating to a dog. It's all to do with statistics, so can anyone shed some light on this please?[/quote]

It's how your disease prevalence (APHA put it at <0.05% for brucella) interacts with your test sensitivity and specificity (APHA suggest about 90% and 99% respectively), such that for very rare things you need very accurate tests, otherwise your false positive numbers start to become significant compared to your true positive numbers and affect the positive predictive value of your test (the percentage of patients with a positive test who actually have the disease).

Similar statistics as when looking at the PPV of FeLV testing when screening in population that has a low prevalence, hence confirmatory testing etc.

For the brucella, the answers as per Mayanth include only sampling from at-risk populations (and at an appropriate time), using the best performing tests (be very cautious about point of care tests) being aware of the limitations of testing etc.

It's also worth reading the latest HAIRS risk assessment https://www.gov.uk/government/publications/hairs-risk-assessment-brucella-canis/hairs-risk-assessment-brucella-canis

RE: How do you interpret/use Brucella blood sampling results?

Mayank Seth — Wed, 06 Dec 2023 15:46:30 GMT

I'm going to refer to my former colleague Emi Barker on this one. Good write up on the BSAVA website: https://www.bsavalibrary.com/content/chapter/10.22233/9781910443514.chap9#html_fulltext

In a nutshell serology is the test of choice and is typically advised in any "at risk" dog. If its negative, you can probably relax. If it's positive then it really depends what test was done and what the prevalence is in the stratified risk population (dog bodrn and bred in the UK with no signs vs a a "rescue dog" from Romania), adjusted for clinical signs and the specificty of the individual test used (AHPA testing more specific than some of the point of care tests that can be used for in-clinic reassurance). The BSAVA page has good guidance on legal and public health implications of a positive dog.

RE: Brucella blood sampling

Neil Wheadon — Tue, 05 Dec 2023 17:53:52 GMT

Serological tests (antibodies) are the most sensitive test to detect dogs with Brucella infection in dogs. PCR testing lacks sensitivity and there is a high risk of false negative and therefore a negative PCR test does not exclude infection. The serological test must be performed by the Animal & Plant Health Agency (APHA) and takes between 7-21 days to return. It requires a single blood sample (2ml serum), which should be submitted to your local APHA laboratory. Please continue to factor this in for routine, non-emergent cases.

The test codes are as follows:

Brucella canis SAT (TC1032) which tests for IgM.
Brucella canis iELISA (TC0116) which tests for IgG.

These can be sent directly to the APHA as per sample submission form LSW008, and costs are as per the APHA Scientific Tests price list (vla.gov.uk). All diagnostic samples should be packaged and dispatched in according with UN3372 packing regulations.

Results should be forwarded to the RDSVS Hospital for Small Animals reception (HFSAreception @ed.ac.uk) with the referral request. Results will be made available to the relevant hospital department and referral can still proceed, albeit with strict barrier nursing in place, in the event of a true positive.

Sadly, both false positive and false negative results can occur. False negatives can arise if testing of the patient was early in the course of infection (within three months of travel) whilst false positives can occur if the patient is concurrently infected with other bacteria (Salmonella). As such we may request that a repeat sample be performed, ideally after three months later to ensure seroconversion.

RE: Brucella blood sampling

Clive Ansell — Tue, 05 Dec 2023 17:13:45 GMT

Brucella Canis Update | The University of Edinburgh

RE: Brucella blood sampling

Clive Ansell — Tue, 05 Dec 2023 17:03:38 GMT

How accurate is a negative result?