Vergleich ausgewählter Blutparameter zur Eignung in der Diagnostik entzündlicher Erkrankungen beim Pferd

Abstract

The aim of the study was to determine the most suitable hematological or biochemical parameter for detection of an inflammatory disorder in horses, regardless of duration of the disease and by using just one sample.
The following parameters were examined: erythrocyte sedimentation rate (ESR), white blood cell (WBC) and differential blood count, total protein, albumin, globulins, fibrinogen and serumproteinelectrophoresis (SPE). Samples were derived from horses divided into 3 groups, according to the results of the clinical examination: group 1 were horses with normal clinical findings (n=300), group 2 consisted of patients with clinically confirmed inflammation (n=107) and in group 3 (n=93) horses diagnosed as suffering from chronic obstructive pulmonary disease (COPD) were summarized.
The use of the ESR for diagnosing inflammatory disorders in horses is discussed in the literature because of the physiologically accelerated settling of erythrocytes in this species and the effects of breed and hematocrit. In the present study, there were no diagnostically usable differences between the 3 groups. An influence of breed was not confirmed.
The results of WBC and differential blood counts showed no relevant differences between the 3 groups. If the upper limit of the normal WBC range is set at 12x10⁹/l in group 2, 52% of horses had a wrong negative result. Furthermore, the results of the present study confirm the observation, that changes in WBC and differential blood counts generally are less marked in horses, than for example in carnivores.
In this study, storage of serum at -18°C has proven, that determination of total protein respectively albumin (methods: biuret resp. bromcresolgreen) was unreliable in frozen samples. Causes for the differences between results before and after storage are unknown and should be evaluated in a following study.
In the present study, total protein and albumin serum concentrations were determined a few hours after taking the samples. The results showed, that dysproteinemias with decrease of albumin and increase of globulins, which are said to be typical in inflammatory conditions, were present in only 45% of horses in group 2. Nevertheless the mean concentration of albumin in group 2 was significantly reduced in comparison to group 1.
Measurement of fractions of globulins was achieved by electrophoresis. In this thesis, there was a significant increase in a- and b-globulins in group 2. It is impossible to compare absolute or relative globulin values between studies because of highly individual division of the electropherogram into fractions. Raised values of g-globulins in chronic inflammation have been reported, but could not be detected in this study probably because of varying duration of the disease in group 2.
Several authors concluded from their studies of the course of continued inflammatory disease, that fibrinogen is an acute-phase-protein (APP) in horses. In the present study, measurement of fibrinogen was helpful to detect an inflammatory disorder, even by examining just a single sample. The mean concentration of fibrinogen (4.03 g/l) in the group 2 was significantly raised in comparison to group 1 (2.52 g/l) and also higher than the reference range (1.5-3.5 g/l). However, even measurement of fibrinogen showed 40% wrong negative results in group 2. Combined consideration of WBC count and fibrinogen reduces the possibility of wrong negative results to 20%.
The analysis of references showed, that the APP serum amyloid A (SAA) could become an important diagnostic aid to specify degree and duration of inflammation. However, a routinely usable method for measurement of SAA in horses still needs to become established. Studies comparing WBC count, fibrinogen and SAA are of special interest and might further reduce the possibility of wrong negative results in laboratory diagnosis of inflammation in horses.
In the present study, there were no relevant differences in the chosen parameters between group 1 and 3. These examinations of bloodsamples are not suitable for diagnosing chronic obstuctive pulmonary disease (COPD). The conclusions of the present study are as follows: 1. measurement of fibrinogen should be added to the routine diagnostic procedures in cases of suspected inflammation in horses, 2. measurement of albumin should be added to that of total protein, 3. measurements of total protein and albumin have to take place in samples which are not stored frozen, and 4. measurement of ESR in horses is worthless at least by using the method of this study.