'Correction' of serum calcium values for albumin biased in geriatric patients

Determination of serum ionized calcium concentration (Cal) is more tedious as a screening method than measuring serum total calcium concentration (CaT) and is not widely practicable. Thus, in clinical practice and even in research, it is customary to 'correct' the serum total calcium concentration (CaT) for that of albumin (Alb) to estimate the 'true' calcemic status,i.e. Cal. However, owing to confounding factors that are incompletely understood at present, the 'corrected' result is imprecise. The hypothesis of the present study was that in geriatric hypoalbuminemia, it could even be biased due to confounding factors associated with aging and related to the Alb level itself. To test this hypothesis, CaT, Alb and Cal were measured in 558 consecutive geriatric in-patients with varying degrees of hypoalbuminemia. The lower the Alb level, the more strikingly the sensitivity of CaT for detecting low Cal was impaired by the correction. In geriatric hypoalbuminemia, the correction is not merely imprecise but even biased (inaccurate). The bias increases with the degree of hypoalbuminemia (i.e. with the need for correction) and leads to underdiagnosis of 'true' (ionic) hypocalcemia.