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(R) (Immediate Response Mobile Analyser) SL (Diametrics Medical Inc. St. Paul, MN, USA), was evaluated and results interpreted with help from data derived on biolog ical variation in five dry cows. The maximum allowable analytical imprecisi on (C-MAX) was estimated as 1.33 % for [Ca++] and 0.12 % for pH; the maxima l allowable analytical inaccuracy (B-MAX) was estimated to be 1.82 % ([Ca+]) and 0.09 % (pH), and the maximum allowable difference between two method s (MAX(DIFF)) was calculated as 0.89 % ([Ca++]) and 0.08 % (pH). These valu es were compared with the coefficient of variation obtained by calculation from analysis results in blood samples obtained from 51 cows, heifers and c alves. The between-cow coefficient of variation (CV), within-cow CV, critic al 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, valu es 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 individua l cow was 5 and 1, respectively. Further, it was observed that, in investig ations of blood Ca++ and blood pH in cattle, neither the use of electrolyte -balanced syringes interchangeable with sodium-heparin vacutainer nor the u se of different blood sampling sites was to be recommended. IRMA(R) SL did not correlate significantly with the chosen reference analyser (Stat Profil e(R) 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(R) SL and Stat Profile(R) 5 Analyser. Analysis on IRMA (R) SL was very easy to perform. It could be a very useful aid in veterinar y clinical practice, when determination of plasma pH in cattle is needed. T he analyser should not yet be applied uncritically with respect to [Ca++] a nalyses in cattle.