What is the evidence for total serum calcium alert list thresholds?

Introduction 

“High risk results” (HRR) are defined as those results requiring immediate medical attention and action due to the high risk of imminent death or major patient harm. Significant inter-laboratory variation in HRR alert list thresholds exists, posing risk to patient safety. Australian pathology professional bodies are now developing an evidence-based guidance document to assist harmonisation of HRR alert list thresholds. Calcium thresholds will be included, as both hyper- and hypocalcaemia carry the risk of developing into life threatening conditions, and there is currently no consensus on upper and lower thresholds. This project aims to provide a comprehensive overview of the evidence for current total serum calcium thresholds, by: i) conducting a systematic literature search for patient-based outcome studies, and ii) examining large hospital datasets to identify the association of critical calcium results with select patient diagnoses, patient demographics and patient outcomes (e.g. length of stay and in-hospital mortality). 

Method 

The systematic review was performed using Medline, EMBASE and Scopus from 1975 through October 2018. Patient admission data from 7 metropolitan and regional NSW hospitals were linked to pathology data and analysed using SPSS. 

Results 

The systematic review found two outcome-based studies, both reporting poor outcomes (mortality) for patients with critically low (≤1.75) or high (≥3.00) calcium results (mmol/L). Analysis of hospital admission data revealed 2.1% of results were considered critically hypocalcaemic and 0.5% was hypercalcaemic from a total of 20696 admissions. The mortality rate was 9.5% (hypocalcaemia) and 18.2% (hypercalcaemia) respectively. 

Discussion 

As numbers of evidence-based studies linking patient outcomes with HRR alert list thresholds are limited, the findings from this investigation may provide preliminary data for future studies relating critical calcium results to poor patient outcomes, such as mortality.