The Utility of Acute-Phase Proteins in the Assessment of Treatment Response in Dogs With Bacterial Pneumonia

Viitanen, S.J.; Lappalainen, A.K.; Christensen, M.B.; Sankari, S.; Rajamäki, M.M.

All measured positive APPs were significantly increased in dogs with BP at presentation compared to healthy controls. This finding is in agreement with previous reports describing CRP and SAA in dogs with BP. 10, 18, 45 Haptoglobin concentrations have not been reported previously, but because significant increases in serum Hp have been reported 24 hours after an inflammatory stimulus, increased concentrations also were expected in BP. 9 However, it must be emphasized that APPs are highly nonspecific inflammatory markers and, in addition to BP, increased concentrations may be encountered in a variety of disease processes. 8, 9 As expected, all positive APPs (CRP, SAA, Hp) correlated positively with each other. However, a negative correlation with albumin did not occur in all comparisons. This is most likely due to the long half-life of albumin, resulting in a late response not noticeable in acute BP. 9 Serum APP concentrations at presentation did not differ significantly in dogs with lsBP and msBP. Additionally, serum CRP, SAA, or Hp at presentation did not correlate significantly with markers of disease severity, such as arterial PaO 2 and the duration of hospitalization. Initial serum CRP, SAA, or Hp concentrations in dogs with BP therefore may not be useful indicators of disease severity. A similar observation has been made in studies describing CRP in human patients with CAP. 46, 47 C-reactive protein and SAA rapidly decreased after initiation of treatment (Fig 2A,B) . These findings indicate that CRP and SAA are useful markers of treatment response. Haptoglobin showed a more gradual increase and decrease and therefore did not reflect clinical recovery as well as CRP and SAA. Because there is a wider range of concentrations and the magnitude of change is more pronounced in SAA compared to CRP, SAA might be a better diagnostic and follow-up marker than CRP in dogs with BP, as already suggested by a recent study comparing CRP and SAA as diagnostic markers of systemic inflammation. 45 Healthy < 2d hosp. > 2d hosp. C-reactive protein continued to increase within the first 24 hours in 5 dogs. This is not unexpected because dogs with BP were presented acutely and CRP is known to reach peak concentrations approximately 24 hours after the onset of an inflammatory stimulus. 48 Consequently, it is not meaningful to interpret the possible CRP decrease as early as 24 hours after initiation of treatment. However, a decrease in serum CRP is expected 48-72 hours after initiation of successful treatment, and a failure to show a decrease has been associated with a poor prognosis in dogs with systemic inflammatory conditions. [22] [23] [24] Consecutive measurements of CRP have been to be found useful in humans with CAP, and the magnitude of CRP decrease at days 3 and 4 has been shown to have prognostic value. 49-51 A connection also has been shown between the pattern of serum CRP concentrations and outcome in humans. Patients with persistently high CRP (so-called nonresponse) or an increase in serum CRP after an initial decrease (so-called biphasic response) during the first days of hospitalization had a poor prognosis. 52 In our study, the CRP ratio, describing the magnitude of decrease after 48 or 72 hours, did not correlate with the duration of hospitalization. This finding could be a consequence of the small number of samples available for CRP measurement at 72 hours: Only 5 dogs with msBP were still alive and hospitalized 72 hours after presentat