Evaluation of a transportable [Ca++] and pH analyser and of the impact of different anticoagulants and sampling sites in cattle.

A mobile, hand-held ionized calcium and pH analyser, the IRMA (Immediate Response Mobile Analyser) SL (Diametrics Medical Inc. St. Paul, MN, USA), was evaluated and results interpreted with help from data derived on biological variation in five dry cows. The maximum allowable analytical imprecision (CMAX) was estimated as 1.33% for [Ca++] and 0.12% for pH; the maximal allowable analytical inaccuracy (BMAX) was estimated to be 1.82% ([Ca++]) and 0.09% (pH), and the maximum allowable difference between two methods (MAXDIFF) was calculated as 0.89% ([Ca++]) and 0.08% (pH). These values were compared with the coefficient of variation obtained by calculation from analysis results in blood samples obtained from 51 cows, heifers and calves. The between-cow coefficient of variation (CV), within-cow CV, critical difference (two-sided) and index of individuality were estimated as 4.77, 2.66 and 14.29%, and 1.08 for [Ca++] analysis. For pH measurements, values of 0.12, 0.24 and 0.96% and 2.95 were estimated. The number of samples required to determine the true value of either [Ca++] or pH in an individual cow was 5 and 1, respectively. Further, it was observed that, in investigations of blood Ca++ and blood pH in cattle, neither the use of electrolyte-balanced syringes interchangeable with sodium-heparin vacutainer nor the use of different blood sampling sites was to be recommended. IRMA SL did not correlate significantly with the chosen reference analyser (Stat Profile 5 Analyser; Nova Biomedical, Waltham, MA) with regard to plasma [Ca++] analyses (correlation coefficient r = -0.24, P = 0.22). However, a significant correlation coefficient (r = 0.63, P < 0.01) was found between analyses of pH performed on IRMA SL and Stat Profile 5 Analyser. Analysis on IRMA SL was very easy to perform. It could be a very useful aid in veterinary clinical practice, when determination of plasma pH in cattle is needed. The analyser should not yet be applied uncritically with respect to [Ca++] analyses in cattle.