Bile acids in cats with portosystemic shunts
Recent cases necessitated a look at the available information on bile acids in cats with shunts. Specifically I wanted to know what are the chances of a cat with suggestive signs having a shunt when bile acids are equivocal. Do ‘normal’ bile acids levels rule out a shunt?
As is often the case there is a lot of extrapolation to do. However, this is a reasonable place to start:
http://europepmc.org/abstract/med/3997624
Published in 1985 these authors looked at a sample of cats with portosystemic shunts and found that:
‘The mean fasting serum bile acid concentration in 4 cats was 24.4 +/- 10.1 mumol/L (normal, 1.7 +/- 0.3 mumol/L) and in 2 of the cats increased to a mean of 120.6 mumol/L (normal, 8.3 +/- 0.8 mumol/L) 2 hours after feeding.’
and concluded that…
‘Used in combination with conventional laboratory tests for hepatic disease, pre- and postprandial serum bile acid concentrations appear to be a sensitive and specific indicator of hepatobiliary dysfunction of value in the diagnosis of PSVA [portosystemic vascular anomalies] in the dog and cat.’
However, I can’t see anything in the data to rule out the possibility that there could be other cats out there with shunts and normal bile acids. This would require prospective imaging or post-mortem studies. Thus the degree of sensitivity seems open to question.
Next up we have:
http://www.ncbi.nlm.nih.gov/pubmed/19709395
…from 2010. Again, the authors were setting out to determine the sensitivity and specificity of serum bile acids in the diagnosis of PSS in cats.
To quote the authors ‘The criteria for inclusion in the study were the results of fasting ammonia and/or serum bile acids measurements. These analytes had been measured because of clinical signs suggestive of hepatic disease or hepatic encephalopathy’.
!
So, not exactly a representative sample of the cat population then. Again it fails to answer my question as to whether I can rule out a shunt if bile acids are normal.
The group of cats with confirmed shunts numbered…….6.
Palerme et al. come at the issue from a different angle.
http://onlinelibrary.wiley.com/doi/10.1111/jvim.12188/pdf
Again they’re clinical patients, not random cats from the general population but the inclusion criterion for these 33 cats is that a splenocaval shunt was identified on ultrasonography. It remains unknown whether these were congenital or acquired shunts. 1.3% of all cats subjected to abdominal ultrasonography for any reason at the University of North Carolina during the study period had splenosystemic shunts.
Importantly, with regard to the two studies above, only 14/33 of these cats had documented hepatobiliary disease. So it would appear that it’s quite common for shunts to go undetected unless prospectively sought.
Sadly, bile acids are available only for 4/33. Two of these had only fasting levels -one cat being within reference and the other slightly over. The other two had pre- and post-prandial: one having slightly elevated values (22 and 35 umol/l) and the other being within reference range.
So that’s not a large population of patients from which to draw conclusions -although hardly much worse than any other information available to us. And 50% of these PSS cats had normal bile acids. I conclude that we don’t know very much but ‘normal’ bile acids do not appear to rule out a shunt in cats.
Our patient here, whose pre- and post-prandial bile acid results were 21 and 51 respectively (reported by the lab as indicating that a shunt was unlikely) underwent surgical attenuation of his left colic-caval shunt last week.
