Researchers from the Queen's Veterinary School Hospital, University of Cambridge, have validated a commercially available ELISA test for measuring 5-hydroxyindoleacetic acid (5-HIAA) in dogs' urine, offering a more accessible way to assess the serotonin metabolite than specialist laboratory methods.

Serotonin has been implicated in several canine diseases, including myxomatous mitral valve disease, pulmonary hypertension and dilated cardiomyopathy, but direct measurement in blood is challenging because of its short half-life in serum.

In humans, urinary 5‑HIAA is considered a more accurate marker of serum serotonin concentration.

However, whilst urine 5-HIAA has previously been measured in dogs using gas chromatography mass spectrometry and high-performance liquid chromatography with electrochemical detection, these techniques are expensive and not widely available.

For the study, which was funded by BSAVA PetSavers and published in the Journal of Small Animal Practice, researchers collected urine samples from 26 dogs undergoing routine diagnostic evaluation at a referral hospital.

Each sample was analysed using both a commercially available ELISA testing kit, BA-E-1900 from Immusmol, and liquid chromatography-tandem mass spectrometry, the current gold standard method.

The ELISA was found to be reliable with acceptable precision and repeatability, particularly at low concentrations, although it had a slightly higher observed error at higher concentrations.

The researchers recommended further validation work to improve understanding of the various preanalytical factors that may influence measurement of 5-HIAA concentrations.

They also said further work should investigate whether measuring urinary 5-HIAA will be a good surrogate marker for physiologically active circulating serotonin in dogs, and whether it will be useful in studying disease pathogenesis.

Dr Penny Watson, senior author of the study, said: "I am very hopeful that, after further validation, this ELISA will prove to be a reliable, simple and cheap test for 5-HIAA in the urine, facilitating further research into the role of serotonin in the pathogenesis of canine diseases.

"We have long suspected that some individual dogs and breeds may have higher circulating serotonin than others and that this might predispose them not only to heart disease but also some common diseases such as chronic pancreatitis and kidney disease.

"They would also be more susceptible to serotinergic syndrome when medicated with drugs such as tramadol or trazadone.

"Further research in this area would thus be directly relevant to small animal practitioners."

https://onlinelibrary.wiley.com/doi/10.1111/jsap.70123