Answers to Quiz Corner

1. E) Conduct the Rivalta test to help distinguish feline infectious peritonitis (FIP) from other causes of peritoneal effusion. Mix 8 mL distilled water with a drop of 98% acetic acid in a clear tube. Carefully layer a drop of effusion on top.

   If the effusion dissolves in solution, the result is negative; if the effusion remains as a drop or ball, or does not dissolve, the result is positive (Figure 2). The Rivalta test is best at ruling out FIP; a negative test means FIP is very unlikely. A positive Rivalta test requires confirmation with other tests for FIP.

   Biopsy with immunohistochemical staining for FCoV antigen or FCoV RT-PCR assays are more sensitive and specific than the Rivalta test but need to be sent to the lab so results take longer.

   References

   1. Thayer V, Gogolski S, Felten S, Hartmann K, Kennedy M, Olah GA. 2022 AAFP/EveryCat Feline Infectious Peritonitis Diagnosis Guidelines. J Feline Med Surg 2022;24:905–933. Available from: https://journals.sagepub.com/doi/epub/10.1177/1098612X221118761. Last accessed January 7, 2025.

   2. Fischer Y, Sauter-Louis C, Hartmann K. Diagnostic accuracy of the Rivalta test for feline infectious peritonitis. Vet Clin Pathol 2012;41:558–67. Available from: https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1939-165X.2012.00464.x. Last accessed January 7, 2025.

2. A) May identify hyperechoic renal cortical changes on ultrasound in dogs within 4 to 6 h of ingestion of ethylene glycol (EG). Cats can have benign hyperechoic renal cortical changes so interpret with caution in this species.

   Ultrasound changes occur due to EG conversion to multiple metabolites, including oxalic acid, which forms calcium oxalate crystals in renal tubules. Crystal accumulation in the kidneys creates the hyperechoic changes.

   Several rapid in-clinic EG tests exist but may give false positive results due to cross-reactivity or sample handling. Ultrasound is one way to help confirm the diagnosis, allowing for prompt intervention.

   Other supportive tests include metabolic acidosis with elevated anion gap, increased serum osmolality, and crystalluria with monohydrate calcium oxalate crystals.

   Azotemia develops in the second stage of toxicity, 1 to 2 d after exposure, and worsens into anuric renal failure and death in stage 3. Renal ultrasound can detect a halo sign when anuria develops around 3 d after ingestion in the dog.

   Ethylene glycol toxicosis does not cause ureteral obstruction/dilation and kidney size is normal to increased. Given the rapid progression of the toxicosis, there is not enough time for stone formation. Free fluid is not expected at this stage, although can develop during treatment with anuria and fluid overload.

   References

   1. Cohn L, Côté E. Clinical Veterinary Advisor: Dogs and Cats. 4th ed., St. Louis, Missouri: Elsevier, 2019:314–315.

   2. Schweighauser A, Francey T. Ethylene glycol poisoning in three dogs: Importance of early diagnosis and role of hemodialysis as a treatment option. Schweiz Arch Tierheilkd. 2016;158:109–114. Available from: https://sat.gstsvs.ch/de/sat/sat-artikel/archiv/2016/022016/ethylene-glycolpoisoning-in-three-dogs-importance-of-early-diagnosisand-role-of-hemodialysis-as-a.html. Last accessed January 8, 2025.

FIGURE 2.

Rivalta test. The effusion in this image contains new methylene blue to improve clarity.

(Image courtesy of Dr. Kalumet — https://commons.wikimedia.org/wiki/File:Rivalta_Probe.jpg).

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