Determination of the calcaemic status of oncology patients at the Charlotte Maxeke Johannesburg academic hospital, using unadjusted serum total calcium

Abstract

Background: When total serum calcium (TCa) is used to determine the calcaemic status of patients, it has to be adjusted, using one of several formulae to limit the effect of low or raised serum albumin levels. All the existing adjustment formulae, were not validated against ionised calcium, neither have they been adjusted for the presence of paraproteins. They have also not been validated for use in cancer patients complicated with chronic kidney disease and cachexia. This study therefore aimed to determine whether unadjusted serum TCa measurement, could be used successfully to determine the calcaemic status instead of the gold standard, ionised calcium (ICa), in two sub-groups of hospital patients with breast cancer (BCA) and multiple myeloma (MM). Material and methods: 202 paired TCa/ICa data points for MM and 3 467 for BCA were reviewed retrospectively over a 1-year period for diagnostic concordance and discordance using ICa as the gold standard. Results: In the MM sub-group, the diagnostic concordance was 60.1% (18 - 59 years) and 78.8% (60 - 90 years) for hypocalcaemia, and 7.4% (18-59 years) and 42.9% (60 -90 years) for hypercalcaemia. Whilst in the BCA sub-group, the diagnostic concordance was 46.1% (18 - 59 years) and 44.5% (60 - 90 years) for hypocalcaemia, and 14.7% (18-59 years) and 21.5% (60 -90 years) for hypercalcaemia. Conclusion: In all cancer sub-groups, both hypocalcaemia and hypercalcaemia were underestimated to various degrees. This was similar to other studies published in non-cancer- specific patients. The poor performance of unadjusted TCa in the study prompted a recommendation that ICa should be used preferentially in cancer patients.