June 29, 2017

Potential Biomarkers of Hypertension in Cats

In some patients, fundic examination reveals signs of hypertensive retinopathy. However, not all cats have these ocular signs.
By Laurie Anne Walden, DVM, ELS
Diagnosing high blood pressure in cats can be difficult. In a study published in the Journal of Veterinary Internal Medicine, researchers investigated whether blood or urine biomarkers could be used to identify feline hypertension. In their test population, some biomarkers were associated with hypertension but none were clinically useful diagnostic tests for high blood pressure.
 
Because cats’ blood pressure often rises in a clinical setting (“white-coat” syndrome), blood pressure measurements may not be accurate. In some patients, fundic examination reveals signs of hypertensive retinopathy (retinal hemorrhages or detachment).

However, not all cats have these ocular signs. “Use of biomarkers would therefore be an attractive alternative to the current way of diagnosing hypertension by repeated blood pressure measurements,” write the authors.

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The investigators studied 4 potential biomarkers of hypertension:
  • Vascular endothelial growth factor (VEGF), which is elevated in humans with hypertension and drops when hypertension is treated
  • N-terminal pro-B-type natriuretic peptide (NT-proBNP), a potential marker of the efficacy of antihypertensive treatment in humans
  • Cardiac troponin I (cTnI), a marker of cardiac cell necrosis in humans and dogs
  • Urine protein to creatinine ratio (UPC), an indicator of kidney damage that has been shown to be elevated in cats with hypertension
 
The authors note that chronic kidney disease can affect levels of these substances. UPC is elevated in cats with chronic kidney disease, potentially decreasing its usefulness as a predictor of hypertension. Renal disease may also decrease the elimination of VEGF, NT-proBNP, and cTnI.
 
The researchers measured concentrations of these substances in 99 cats classified into 4 groups: healthy geriatric, normotensive with chronic kidney disease, hypertensive with hypertensive ocular damage, and hypertensive without ocular damage. Cats were client-owned pets seen at 2 primary care practices in London. Ocular evidence of hypertension was identified on indirect fundoscopy. Blood pressure was measured by the Doppler technique. Cats known to have hyperthyroidism were excluded.
 
The statistical analysis revealed the following:
  • In the healthy geriatric group, mean plasma urea and creatinine concentrations were significantly lower than in the other 3 groups, and urine specific gravity was significantly higher.
  • VEGF concentration was an independent predictor of hypertension. It was also an independent predictor of hypertensive ocular damage, but this was not significant on multivariable analysis.
  • NT-proBNP was significantly higher in cats with ocular signs of hypertension than in healthy cats, but it was not an independent predictor of hypertension or of hypertensive ocular damage.
  • cTnI was significantly lower in healthy cats than in the other 3 groups and was an independent predictor of hypertension. However, cTnI was not significantly higher in hypertensive cats than in the group with chronic kidney disease and normal blood pressure. The authors suggest that underlying chronic kidney disease was responsible for the elevations in cTnI in all but the healthy group.
  • UPC was not significantly different between groups and was not a significant predictor of hypertension or of hypertensive ocular damage.
  • In cats with hypertension, amlodipine treatment significantly decreased NT-proBNP concentration but did not alter VEGF or cTnI.
 
Although some of the statistical results for VEGF, NT-proBNP, and cTnI seemed to suggest that these markers could be used to diagnose or manage hypertension, their sensitivity was low, say the authors. “When assessing the [sensitivity and specificity], none of the biomarkers alone met the criteria to diagnose hypertension,” they write.
 
“One cannot argue in favor of replacing a noninvasive method (retinal examination) with an invasive blood test with a lower sensitivity and specificity,” conclude the authors. They add, “These biomarkers are unlikely to be of clinical utility in the differentiation of white-coat from true hypertension” in cats that do not have hypertensive retinopathy.
 
 
Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.

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