Serum ionized calcium levels may be more closely related to the admission QTc interval than total calcium levels in patients hospitalized with COVID-19

INTRODUCTION: Hypocalcemia prolongs the QTc interval. Total calcium (TCa) measurement can be misleading in cases where the concentration of albumin is abnormal. We aimed to investigate which calcium level—ionised calcium (iCa) or TCa—may be more closely related to the QTc interval in COVID-19 patients in whom hypocalcemia and hypoalbuminemia are observed frequently.
METHODS: Adult patients hospitalised for COVID-19 were included in this study. ICa levels were obtained from the venous blood gas sample examined during the emergency department admission, and the TCa levels were obtained from the biochemistry results on admission. The pH-adjusted iCa (Corrected-iCa) and albumin-adjusted TCa (corrected-TCa) were calculated. The QT interval was measured from the admission ECG and corrected for heart rate using the Bazett formula.
RESULTS: Hundred and thirty-two patients were included in the study. The mean age was 50±19 years, and 62 (47%) patients were female. Median iCa level was 1,13 mmol/L (1,08-1,18 IQR), median TCa level was 2.13 mmol/L (2.02-2.22 IQR). 76 patients (57%) had hypocalcemia (iCa<1,16 mmol/L). The median QTc interval was 431 ms (414-450 IQR). In the multivariable linear regression analysis, a significant relationship was observed between the QTc interval and iCa and corrected-iCa levels (β=-2.22, SE=27.839, p=0.028, β=-2.16, SE=29.407, p=0.033), but no significant relationship was observed between TCa and corrected-TCa levels (β=-1.02, SE=3.959, p=0.312, β=-0.44, SE=4.635, p=0,650).
DISCUSSION AND CONCLUSION: A significant relationship was observed between iCa levels and the QTc interval, which was longer in patients with hypocalcemia, but there was no significant relationship observed with TCa levels.