The ‘inflammatory profile’ is generally used in the common practice situation of non-specific lethargy/dullness when infectious challenge is an important differential diagnosis. The acute inflammatory reaction results in a widespread and complex cascade of cytokine and lymphokine production (interleukins, interferons, eicosanoids etc..) leading to many potentially detectable changes in the blood. The commonest changes to be used clinically are neutrophilia and acute phase protein responses. Acute phase proteins are a wide array of proteins which are synthesised and released from the liver in response to inflammatory cytokines (especially interleukin-6). These proteins include fibrinogen, serum amyloid A, caeruloplasmin, C-reactive protein, haptoglobin and several others. A large selection of these acute phase proteins is commonly used in human clinical pathology although only fibrinogen is assayed widely in veterinary laboratories. The Liphook Equine Hospital Laboratory is one of only a few veterinary laboratories to offer serum amyloid A as an additional acute phase protein and further proteins are under investigation such as C-reactive protein and procalcitonin.
Fibrinogen - normally between 1-4 g/l and may rise as high as 10-15 g/l in severe inflammatory cases. Therefore the ‘pathophysiological range is approximately 4-8X normal. Values greater than 10 g/l must always be regarded seriously and carry a guarded (but not necessarily poor) prognosis. Fibrinogen responds to acute inflammation relatively sluggishly and may not be outside the reference range for 24-48 hours following initiation of an acute inflammatory response.
Serum amyloid A - We have been using SAA at the Liphook Equine Hospital Laboratory for approximately 2½ years now. We have found the test both reliable and sensitive to acute inflammation in horses and it has become our preferred diagnostic and monitoring acute phase protein in cases such as viral/bacterial respiratory disease, peritonitis, colitis etc…. Most normal horses have SAA concentrations around 5 ?g/ml and with severe inflammatory disorders this can rise to approximately 1000 mcg/ml creating a pathophysiological range of about 200X normal. Compared with fibrinogen this allows a far greater ‘grading’ of severity of the inflammatory process and more sensitive monitoring of progress.
© The Liphook Equine Hospital 2009
