Utvärdering av en snabbtest för diagnostisering av hypokalcemi hos nötkreatur

Abstract: Clinical signs of hypocalcaemia in dairy cows are easily recognized, and a rapid response to treatment generally confirms the diagnosis in the field. However, clinical signs of other disorders in cows, such as toxemia, calving paralysis, or muscoskeletal injury, may mimic those associated with hypocalcaemia. Therefore, making a diagnosis of hypocalcaemia on the basis of clinical signs alone may be difficult. In ambulatory veterinary practices, cow-side tests are useful to make the diagnosis and prognosis easier. Kruuse's Kalcium Test is a cow-side test based on the principle that calcium ions are necessary for coagulation of blood, and that chelation with EDTA prevent coagulation. It consists of a test tube prepared with EDTA and thrombin to which 10 ml blood is added. According to the manufacturer's instructions, the test result shall be evaluated after 5 minutes. Serum calcium concentration is estimated to be greater than or less than, 1,75 mmol/l. The aim of this study was to evaluate the accuracy of Kruuse's Kalcium Test, in its ability to identify hypocalcaemic cows. Two different cut-off values (1,75 and 2,1 mmol/l) of the reference test were used to show the clinical usefulness for the cow-side test. Blood were collected from 42 dairy cows, of which 11 had clinical signs of hypocalcaemia, 5 suffered from other diseases and 26 were clinically healthy. Ten ml was used directly to perform the kalcitest. The rest was kept for later serum-Ca analysis. Initially the cow-side test was evaluated after five minutes. When 21 samples were analysed, the preliminary results indicated a high proportion of false positive test results. Therefore the remaining samples (n=21) of the tests were evaluated at 5, 6, 7, 8, 9, and 10 minutes. The test results were compared with serum calcium concentration. Sensitivity, specificity, and predictive values of positive and negative test results were calculated on the basis of Kruuse's Kalcium test results and two different serum calcium levels (1,75 and 2,1 mmol/l). When the time for evaluating the cow-side test was prolonged from 5 to 10 minutes, the specificity increased from 18 % to 100 % and the sensitivity decreased from 100 % to 80 %. In Sweden, a cow is often considered to be hypocalcaemic if the serum calcium value is lower than 2,1 mmol/l. The specificity was 100 % and the sensitivity was 62 % after ten minutes using this cut-off value.