Method for the determination of ionized calcium in clinical practice

: The authors give an account of their experience with the problem of assessment of ionized calcium (Ca2+) in clinical work. To assess Ca2+ they use an ICA 2 analyzer of Radiometer Co. Copenhagen which makes it possible to assess concurrently the Ca2+ concentration at a given pH (Ca2+/act. pH), pH and Ca2+ calculated for pH 7.4 (Ca2+/pH 7.4) in capillary and venous blood. The authors confirmed the significant difference between Ca2+/act. pH in venous and capillary blood which is due to the pH and they did not find a significant difference in Ca2+/pH 7.4 in venous and capillary blood. They found that the specimens of capillary blood can be kept in capillaries in the refrigerator at +4 degrees C for four hours without a significant changes of the Ca2+/act.pH level. During subsequent time intervals, i.e. after 24, 48 and 72 hours following collection of the blood sample, there is a significant rise of Ca2+/act.pH due in particular to a significant drop of the pH of the blood samples. The Ca2+/pH 7.4. concentration in capillary blood does not change throughout the 72-hour follow up period. The authors provided also evidence that slight physical strain (30 min. walk on flat ground) does not cause significant changes in the concentration of capillary Ca2+/act.pH nor of Ca2+/pH 7.4 due to the three-minute compression of the arm by the tonometer cuff with a pressure equal to the diastolic blood pressure of the examined subject. The reported results make simpler and more accurate assessment of Ca2+ in clinical and ambulatory practice possible.