Filtering clinically significant hypercalcaemia from non-significant hypercalcaemia at the laboratory level

Abstract

In an earlier study it was shown, that, in a hospital population, only about 30 % of patients with hypercalcaemia had the diagnosis identified and so an alarm filter was developed, at the laboratory level, to differentiate between clinically significant and clinically non-significant hypercalcaemia. The filter correctly classified 84% and 77% of women and men with hypercalcaemia, respectively, with respect to the clinical significance of the hypercalcaemia. The sensitivity and the specificity of the discriminant functions were 90 % and 73 % in women and 80 % and 67 % in men.

The alarm filter was based on a two-step procedure. The patients were primarily classified by the discriminant functions into one of the following medical diagnoses related to hypercalcaemia: primary hyperparathyroidism, malignancy, and transient hypercalcaemia. Based on this classification the patients were characterized as having either a clinically significant or non-significant hypercalcaemia. The alarm filter was based on two discriminant functions. The discriminant variables were phosphate, albumin, protein, LD, and a haemoglobin in women, and albumin, protein, ALP, and age in men. Missing values were estimated. The discriminant variables were selected from 17 possible discriminant variables, all measured by routine, and age. The study group comprised 257 patients with hypercalcaemia, consecutively registered, during half a year. The classification efficiency of the discriminant functions were based on comparison of results obtained by cross-validation of the discriminant functions, and the medical diagnosis decided by the clinicians in the respective departments of the hospital. The medical diagnoses were based on principles and definitions generally used in the departments with no knowledge of the results assessed by the discriminant functions.

Key Words:

• classification
• clinically significant hypercalcaemia
• discriminant functions
• transient hypercalcaemia