Nomograms for calculating the concentration of ionized calcium of human blood plasma from total calcium, total protein and/or albumin, and pH

Abstract

Two nomograms are described. One is a Cartesian nomogram similar to the original McLean-Hastings nomogram but supplemented by an albumin scale and a pH scale to allow calculations in case of an abnormal albumin/globulin ratio or an abnormal pH. The other is an alignment nomogram. The underlying arithmetic equations, which are slightly different for the two nomograms are described. Both refer to 37°C. Calculated and measured ionized calcium are compared for 24 specimens and it is concluded that the calculated value may be subject to a considerable bias amounting to 0.2 mmol/1 in the worst cases. Nomograms size A4 and BASIC program are available on request.

Key words:

• Blood
• protein
• albumin
• hydrogen-ion concentration