Kinetics of serum amyloid A during the treatment period of foals with pneumonia

Summary: The ultrasonographic examination of foals with pneumonia has been proven successful in monitoring the course of the disease during treatment. However, the question arises whether another parameter, such as the acute phase protein serum amyloid A (SAA), could also be suitable for evaluating the response to treatment, the course during treatment or the decision to terminate the treatment in foals with pneumonia. The course of moderate or severe pneumonia was recorded by several diagnostic tests in a prospective study performed on 52 foals. Clinical and ultrasonographical examination of the thorax and blood values (SAA, white blood cell count) of these foals were measured on the day of diagnosis and weekly during treatment. Foals with a pulmonary abscess score of 15–19.5 cm determined by sonography of the thorax (moderate pneumonia) were assigned to group 1 (n = 31) and received a treatment with rifampin and tulathromycin. If the abscess score was > 20 cm (severe pneumonia), the foals were included in group 2 (n = 21) and were treated with rifampin and azithromycin. All foals recovered during the treatment period. Sonography of the thorax of the foals with moderate pneumonia (group 1) showed no more pathologic findings after ten days, and the foals with severe pneumonia (group 2) after eleven days of treatment. At diagnosis the median SAA value at diagnosis was 367 mg/L (median; 25th/75th: 23–937) in foals with moderate pneumonia and 216 mg/L (median; 25th/75th: 16–690) in those with severe pneumonia. The SAA values of foals with initially elevated values decreased significantly until they reached normal values < 40 mg/L after five days in the foals with moderate pneumonia and four days in the those with severe pneumonia. The time between the day SAA reached normal values and ultrasonography of the lung revealed no more abnormalities was three days in foals with moderate pneumonia and seven days in those with severe pneumonia. The SAA as a diagnostic method had a sensitivity of 68 % in the case of moderate pneumonia and 71 % in the case of severe pneumonia on the day of diagnosis. If only the foals with pneumonia and fever were considered, 91 % showed an initially increased SAA. During treatment, the SAA correlated with the abscess score, the clinical score and the age at diagnosis, but not with the number of white blood cells. In conclusion, the ultrasonographic examination remains the most precise tool to diagnose pneumonia and follow its progress during treatment in foals. However, the SAA can be used as an additional parameter for evaluating the treatment success. Especially foals with fever and younger foals show high SAA values in patients with pneumonia. By observing the kinetics of SAA in a patient, this blood parameter could be a support to adjust the date of the final ultrasonographic examination. Thereby, the duration of treatment can be individually adapted.