Coronavirus disease 2019 (COVID-19), caused by the Severe Acute Respiratory Syndrome
Coronavirus 2 (SARS-CoV-2), presents primarily with fever, dry cough, and fatigue
or myalgia [1]. Although most patients have a favorable prognosis, infection may not
infrequently lead to a severe syndrome requiring hospitalization and assisted ventilation
with high lethality [2].
Previous studies have reported that calcium played a central role in viral infectious
and replicative mechanisms of SARS-CoV, MERS-CoV, and Ebolavirus [3–5]. In a large
group of SARS patients in North America, hypocalcemia was detected in 60% of patients
at hospital admission and in 70% during hospitalization [6]. Moreover, data from patients
with Ebolavirus infection in United States and European hospitals reported a similar
incidence of hypocalcemia [7].
Several studies investigated so far the clinical and laboratory characteristics of
COVID-19 patients, including inflammatory and organ injury biomarkers [8]. Recently,
we have reported the first case of COVID-19 presenting with severe hypocalcemia [9].
However, no population data are available on calcium levels in COVID-19 [10].
The aim of our study was to investigate the incidence of hypocalcemia in a large single
center population of COVID-19 patients and evaluate its possible clinical implications.
Methods
We conducted a retrospective cohort study at IRCCS San Raffaele Hospital, a tertiary
health-care hospital in Milan, Italy. We included patients (aged ≥ 18 years) with
COVID-19 admitted to our Emergency Department (ED). We excluded COVID-19 patients
transferred from other hospitals and patients initially hospitalized for other diseases.
Only patients with serum ionized calcium data from arterial blood gas tests performed
at initial evaluation in the ED were included. Ionized calcium levels were expressed
both as actually measured levels (AC) and as adjusted mathematically to a standardized
pH of 7.4. levels (SC) to avoid influence of sample handling. Hypocalcemia was defined
as calcium level below 1.18 mmol/L (RapidPoint 500 Analyzer, VA, USA).
We excluded patients with comorbidities and concomitant therapies influencing calcium
metabolism: chronic kidney disease, osteoporosis, patients on glucocorticoids and
antiepileptic drugs, vitamin D/calcium, loop/thiazide diuretics, and patients with
an eGFR≤30 mL/min/1.73 m2 using creatinine levels at initial evaluation. Assessed
outcomes included hospitalization, intensive care unit (ICU) admission and death.
This study is part of the COVID-19 Biobank study, which is registered with ClinicalTrials.gov,
NCT04318366 and obtained specific approval by the local EC.
Statistical analysis was conducted with SPSS 23.0 version (Chicago, USA). Categorical
variables were indicated as frequency (%) and continuous variables as medians (IQR).
Differences in variable frequencies between groups were calculated using the Fisher
test and the Mann–Whitney U test for continuous variables. All statistical tests were
two-sided. A p value of <0.05 was considered statistically significant. Linear regression
analyses were used to correlate continuous variables. Univariate and multivariate
analyses performing binary logistic regression were used to calculate adjusted odds
ratios (ORs) with 95% confidence intervals (CIs).
Results
A total of 531 patients were included in the study. Demographic and clinical patients’
characteristics are summarized in Table 1. On initial hospital evaluation, median
AC level was 1.1 mmol/L [1.07–1.15] and SC level was 1.14 mmol/L [1.1–1.17]. Hypocalcemia
was found in 462 patients (82%) with AC levels, in 414 (78.6%) patients with SC levels.
Using AC levels 18 patients (3.4%) presented a severe hypocalcemia with values lower
than 0.99 mmol/L, using SC this was found in 10 patients (1.9%).
Table 1
Baseline characteristics of patients with Covid-19 included in the study
No. (%)
Demographic information
Total No.
531
Age, median (IQR), year
59 (50–69)
Gender
Female
171 (32.2%)
Male
360 (67.8%)
Ethnicity
Caucasian
449 (84.6%)
Latin American
70 (13.2%)
Asian
8 (1.5%)
Sub-Saharan African
4 (0.8%)
BMI, median (IQR), kg/m2
27 (24–30)
Comorbidities
Total No.
531
Hypertension
177 (33.3%)
Coronary artery disease
34 (6.4%)
Diabetes
Type 1
5 (0.9%)
Type 2
68 (12.8%
Cancera
11 (2.1%)
Chronic obstructive pulmonary disease
10 (1.8%)
Neurological disabilities
11 (2.1%)
Laboratory results at admission
pH, median (IQR)
7.47 (7.44–7.5)
Ionized calcium levels, median (IQR), mmol/L
Actual calcium
1.1 (1.07–1.15)
Standardized calcium
1.14 (1.1–1.17)
eGFR, median (IQR), mL/min/1.73 m2
85 (68.8–97.7)
Total calcium levelsb, median (IQR), mmol/L
2.14 (2.05–2.2)
LDH, median (IQR), U/L
359 (273–457)
CRP, median (IQR), mg/L
66 (26.2–123.4)
BMI body mass index; COVID-19 coronavirus disease 2019, IQR interquartile range
aOnly active neoplasms were included in this section
bCalcium values at admission have not been corrected for serum albumin
Hypocalcemic patients were more frequently males (AC, 69% vs 57% p = 0.06; SC, 70%
vs 60% p = 0.046) and older (AC, 59 years [51–69] vs 53 years [45–67] p = 0.01). LDH
and CRP levels were very significantly higher in hypocalcemic vs normocalcemic patients
(Fig. 1). Moreover, linear regression analyses showed a negative correlation of calcium
levels with LDH (AC, p < 0.001, r
2 = 0.074; SC, p < 0.001, r
2 = 0.055) and CRP levels (AC, p < 0.001, r
2 = 0.038; SC, p < 0.001, r
2 = 0.025).
Fig. 1
Inflammatory parameters in patients with (YES) or without (NO) hypocalcemia based
on actual and standardized ionized calcium levels
Four hundred twenty-four patients (79.8%) were hospitalized after initial evaluation,
they had significantly lower ionized calcium levels as compared to non-hospitalized
patients (AC, 1.1 [1.06–1.4] vs 1.14 (1.1–1.18] mmoll/L, p < 0.001; SC, 1.13 [1.1–1.17]
vs 1.16 [1.12–1.2] mmol/L, p < 0.001). In univariate and multivariate analyses, hypocalcemia
was an independent risk factor highly associated with hospitalization (AC, p < 0.001
SC, p < 0.001) (Table 2).
Table 2
Multivariate analyses of possible risk factors for hospitalization in our study population
Variables*
Odds ratio [95% confidence interval]
p value
A. Age
1.06 [1.03-1.09]
p
< 0.001
Male gender
1.83 [1.002-3.35]
p
= 0.049
Hypertension
1.3 [0.63–2.69]
p = 0.46
Coronary artery disease
1.59 [0.38–6.6]
p = 0.52
Type 2 diabetes
2.24 [0.75–6.6]
p = 0.15
Hypocalcemia (AC)
2.27 [2.72–11.6]
p
< 0.001
eGFR
1 [0.99–1.02]
p = 0.42
LDH
1.004 [1.001–1.007]
p
= 0.004
CRP
1.008 [1.002–1.014]
p
= 0.011
B. Age
1.06 [1.03–1.09]
p
< 0.001
Male gender
1.67 [0.91–3.0.6]
p = 0.097
Hypertension
1.23 [0.59–2.52]
p = 0.57
Coronary artery disease
1.83 [0.45–7.47]
p = 0.4
Type 2 diabetes
1.95 [0.67–5.61]
p = 0.22
Hypocalcemia (SC)
4.15 [2.21–7.78]
p
< 0.001
eGFR
0.99 [0.98–1.01]
p = 0.46
LDH
1.005 [1.002–1.008]
p
= 0.003
CRP
1.009 [1.002–1.015]
p
= 0.006
*Only variables with p < 0.3 in univariate analyses were included in multivariate
analyses. Section A: hypocalcemia based on AC; section B: hypocalcemia based on SC.
P values reported in bold are those statistically significant.
Thirty-four patients (11.6%) and 33 patients (11.5%), based on AC or SC levels, respectively,
developed severe hypocalcemia during hospitalization.
Fifty-eight out of 531 patients died (11.5%) and 62 (11.7%) were admitted to ICU.
Hypocalcemia at initial evaluation was significantly (p < 0.05) associated with these
two outcomes only in univariate analyses (death: AC, OR 4.9 CI 95% [1.18–20.8]; SC,
OR 2.6 CI 95% [1.1–6.32]; ICU admission: AC, OR 5 CI 95% [1.19–20.9], SC, OR 2.7 CI
95% [1.14–6.5]) but not in multivariate analyses.
Discussion
In previous studies, hypocalcemia was associated with higher mortality and poor clinical
outcome in hospitalized and critically ill patients [11, 12].
Several reports demonstrated a crucial role of calcium in viral fusion for different
enveloped viruses such as SARS-CoV, MERS-CoV, and Ebolavirus [3–5]. Calcium directly
interacted with fusion peptides of these viruses promoting their replication [3–5].
Moreover, in SARS-CoV and Ebolavirus patients, hypocalcemia was a very frequent laboratory
finding although its mechanistic and clinical relevance as well as its prognostic
significance were not fully elucidated [6, 7].
Surprisingly, so far despite the already extensive literature available in COVID-19
and its related biochemical markers of activity and prognosis, no peer reviewed published
data are yet available on calcium levels in this emerging disease. Only recently we
observed a patient with COVID-19 presenting with severe hypocalcemia who had in the
history total-thyroidectomy as risk factor for subclinical hypoparathyroidism [13].
Therefore, to our knowledge this is the first study that revealed a very high incidence
of hypocalcemia in a large monocentric population of COVID-19 patients at initial
hospital evaluation. The observed rate of hypocalcemia was higher in comparison to
the previous studies in SARS-CoV and Ebolavirus patients and this could be explained
partly because we used serum ionized calcium levels, a more reliable measure than
total calcium levels corrected for albumin. Moreover, highly prevalent hypovitaminosis
D in the northern regions of Italy may be a predisposing factor in our study population
[14].
Calcium levels at initial evaluation were lower in finally hospitalized vs non-hospitalized
patients, and hypocalcemia was found to be an independent risk factor for hospitalization.
Moreover, the strong association between high LDH and CRP levels and low calcium levels
which can be observed in Tumor Lysis Syndrome [15] may support the definition of COVID-19
as a Cytopathic Viral lysis syndrome. This suggests a possible role of ionized calcium
as useful biochemical marker of disease aggressiveness, since also easy to measure
in emergency, helping clinicians in identifying severe patients at initial hospital
evaluation. Moreover, the relative high proportion of patients who developed severe
hypocalcemia during hospitalization supports its specific relevance to the disease.
In univariate analyses hypocalcemia was also found to be associated with mortality
and ICU admission, but this was not maintained in multivariate analyses likely, due
to many other interfering factors included different therapeutic approaches.
In conclusion, since hypocalcemia is highly incident in COVID-19 patients and predicts
the need for hospitalization we suggest that ionized calcium should always be assessed
at initial hospital evaluation in order to identify more severe patients. Finally,
since hypocalcemia may have negative impact on cardiac outcomes and may be even lethal
when severe and acute we suggest calcium monitoring and adequate supplementation when
indicated in all hospitalized patients with COVID-19 [13].