Table 2 The features of articles included in the meta-analyses

Samin et al., 2022 [20]

Pakistan

Retrospective/Observational study

120

70 diabetic patients (including 20 newly diagnosed with type II diabetes mellitus), 50 non-diabetic patients

Mean age of 48.14 ± 16.51 years

52 cases (43.3%) had hypertension, 39 cases (32.5%) had cardiovascular diseases

Not explicitly detailed, but adverse outcomes and complications were measured

Mortality rate was higher in diabetic patients (57.1%) compared to non-diabetic patients (22%)

Diabetic patients had a significantly longer hospital stay compared to non-diabetic patients

Bode et al., 2020 [23]

United States

Retrospective observational study

887

451 patients with diabetes and/or uncontrolled hyperglycemia, 386 patients without diabetes or hyperglycemia

Not specified

Diabetes, uncontrolled hyperglycemia (defined as ≥ 2 blood glucose readings > 180 mg/dL within any 24-h period)

Glycemic control issues among hospitalized COVID-19 patients; data focused on blood glucose levels

Mortality rate was 28.8% in diabetes and/or uncontrolled hyperglycemia patients compared to 6.2% in patients without these conditions; 41.7% mortality in uncontrolled hyperglycemia patients, 14.8% in diabetes patients

Longer median length of stay (LOS) for patients with diabetes and/or uncontrolled hyperglycemia (5.7 days) compared to patients without these conditions (4.3 days)

Alshukry et al., 2021 [22]

Kuwait

Single-center, retrospective study

417

The study compares diabetic and non-diabetic COVID-19 patients

The study does not specify the age distribution, but age-related details might have been considered in relation to outcomes

Diabetic COVID-19 patients had a significantly higher prevalence of comorbidities, particularly hypertension. They also showed higher levels of C-reactive protein and lower estimated glomerular filtration rates, indicating more severe complications

The study did not specifically detail the symptoms but highlighted that diabetic patients experienced more severe disease outcomes

Diabetic COVID-19 patients had significantly higher ICU admission rates (42.4% vs. 7.7%) and mortality rates (34.7% vs. 3.7%) compared to non-diabetic patients

Diabetic COVID-19 patients required more intensive care, as indicated by higher ICU admissions and an increased need for managing complications associated with diabetes. Every 1 mmol/L increase in fasting blood glucose was associated with a 1.52 times higher risk of mortality from COVID-19

Ortega et al., 2022 [24]

Spain

Cross-sectional study

2,069

The study compared outcomes between patients with and without diabetes

Patients with DM were, on average, 5.1 years older than those without DM

The study found that diabetes was independently associated with higher mortality and the need for invasive mechanical ventilation (IMV). Key factors associated with poor outcomes in diabetic patients included being over 65 years old, male, and having pre-existing chronic kidney disease. There was a nonlinear relationship between admission blood glucose levels and the risk of in-hospital mortality or death/IMV

Specific symptoms were not detailed in the summary, but the study focused on severe in-hospital complications

The overall in-hospital mortality was 18.6%, with higher mortality among patients with DM (26.3%) compared to those without DM (11.3%). Diabetes was associated with a higher risk of death (OR = 2.33) and death or IMV (OR = 2.11)

Higher blood glucose levels on admission were associated with worse outcomes, suggesting the need for personalized glycemic optimization to improve outcomes during hospitalization

Akbariqomi et al., 2020 [25]

Iran

Retrospective, single-center study

595

The study included 148 patients with diabetes (24.9%) and compared them to 447 patients without diabetes

The median age of the patients was 55 years

Diabetic patients had more comorbidities, particularly hypertension (48.6% vs. 22.3%). They also exhibited higher levels of white blood cell count, neutrophil count, C-reactive protein, erythrocyte sedimentation rate, and blood urea nitrogen. Diabetic patients had a higher proportion of patchy ground-glass opacity in chest CT scans (52.7% vs. 25.7%). Complications were more common, and the need for respiratory support was higher among diabetic patients

The most common symptoms were fever (70.4%), dry cough (61.8%), and dyspnea (61%)

Mortality was significantly higher in patients with diabetes (17.8%) compared to those without diabetes (8.7%)

Patients with diabetes required more respiratory support and had a higher rate of treatment failure compared to non-diabetic patients

Espiritu et al., 2021 [28]

Philippines

Nationwide, comparative, retrospective cohort study

10,881

Diabetes/Non-Diabetes: 2,191 patients with diabetes (DM) and 8,690 without diabetes (non-DM)

Median age of DM cohort was 61 years, with over 50% above 60 years old; female-to-male ratio was 1:1.25

Focused on diabetes mellitus (DM)

Not explicitly detailed, but adverse outcomes and complications were measured

Mortality: Adjusted odds ratio (aOR) for mortality in the DM group was significantly higher at 1.46 (95% CI 1.28–1.68; p < 0.001) compared to the non-DM group

Respiratory Failure: aOR for respiratory failure was 1.67 (95% CI 1.46–1.90) higher in the DM group

Severe COVID-19: aOR for developing severe/critical COVID-19 was 1.85 (95% CI 1.65–2.07; p < 0.001) higher in the DM group

ICU Admission: aOR for ICU admission was 1.80 (95% CI 1.59–2.05) higher in the DM group

Ventilator Dependence: DM patients had significantly longer duration of ventilator dependence (aOR 1.33, 95% CI 1.08–1.64; p = 0.008)

Length of Hospital Stay: DM patients had longer hospital admissions (aOR 1.13, 95% CI 1.01–1.26; p = 0.027)

The presence of diabetes mellitus (DM) in COVID-19 patients significantly increased the risk of mortality, respiratory failure, severe/critical COVID-19, ICU admission, ventilator dependence, and longer hospital stays compared to non-DM patients

Austin et al., 2022 [19]

United States

Observational cohort study

1,439,520

The study compares COVID-19 outcomes between beneficiaries with and without diabetes mellitus

Diabetic beneficiaries were younger compared to non-diabetic beneficiaries

Diabetic beneficiaries had more comorbidities, higher rates of Medicare-Medicaid dual eligibility, and were more likely to be Black

They also had worse hospitalization outcomes, including higher rates of ICU admissions and in-hospital complications

The study focuses on disease severity and outcomes rather than specific symptoms

Diabetic beneficiaries had higher overall mortality following a COVID-19 diagnosis (17.3% vs. 14.9%)

Diabetic beneficiaries had higher hospitalization rates (20.5% vs. 17.1%), more ICU admissions (7.78% vs. 6.11%), more ambulatory care visits (8.9 vs. 7.8), and higher ICU mortality (2.41% vs. 1.77%)

Long et al., 2022 [29]

Not specified

Multicenter study

2,330

336 patients with diabetes mellitus (DM), 1344 non-diabetic patients matched by age and sex

Age-stratified analysis conducted (specific age range not provided)

Higher rates of intensive care unit (ICU) admission (12.43% vs. 6.58%), kidney failure (9.20% vs. 4.05%), and mortality (25.00% vs. 18.15%) in DM patients compared to non-DM patients; hyperglycemia was associated with adverse outcomes in both DM and non-DM patients

Severe pneumonia associated with hyperglycemia

Mortality was higher in DM patients (25.00%) compared to non-DM patients (18.15%); hazard ratios for adverse prognosis were 10.41 for diabetes and 3.58 for hyperglycemia

Higher ICU admission rates and increased laboratory abnormalities (e.g., lymphocyte and neutrophil percentage, C-reactive protein, urea nitrogen) in DM and hyperglycemic patients

Heald et al., 2022 [27]

United Kingdom

Urban population study using electronic health record data

53,390

Diabetes: 13,807 individuals with type 2 diabetes mellitus (T2DM)

Non-Diabetes Controls: 39,583 COVID-19-infected individuals without diabetes

The study does not provide specific age details but included a broad population in Greater Manchester

Increased Mortality Risk: Higher in those with chronic obstructive pulmonary disease (COPD), severe enduring mental illness, and those taking aspirin/clopidogrel/insulin

Associated with Higher Mortality: Lower estimated glomerular filtration rate (eGFR), hypertension, smoking

Protective Factors: Taking metformin, sodium-glucose cotransporter 2 inhibitors (SGLT2i), or glucagon-like peptide 1 (GLP-1) agonists was associated with reduced mortality risk

The study did not specify symptoms but focused on mortality and associated factors

Mortality Rate for T2DM: 7.7% after a positive COVID-19 test

Mortality Rate for Non-Diabetes Controls: 6.0%

Relative Risk (RR) of Death for T2DM: 1.28 compared to non-diabetes controls

Predictive Factors for Higher Mortality: Age, male gender, and social deprivation (higher Townsend score) were significant

Protective Measures: Prescription of specific medications (metformin, SGLT2i, GLP-1 agonists) and non-smoking status were associated with reduced mortality risk

Altin et al., 2022 [26]

Turkey

Retrospective observational study

341

Diabetic: 120 patients

Non-Diabetic: 221 patients

Not specified

More susceptible to severe COVID-19 infection and increased need for oxygen therapy

Poorly Controlled Diabetes: Associated with longer hospitalization compared to well-controlled diabetes

Severe disease (47.5% in diabetics vs. 27.8% in non-diabetics), higher need for oxygen therapy (51.2% in diabetics vs. 29.4% in non-diabetics)

No significant difference in mortality rates between diabetic and non-diabetic patients

Diabetic patients had a median hospitalization duration of 8 days (longer than non-diabetics at 7 days). Poorly controlled diabetic patients had a longer median hospitalization duration (9 days) compared to well-controlled diabetic patients (8 days) Intensive monitoring and disease management recommended for diabetic patients with comorbidities

Moftakhar et al., 2021 [21]

Iran

Retrospective observational study

16,391

1,365 individuals with diabetes

15,026 individuals without diabetes

Diabetic Patients: Average age of 59 years

Non-Diabetic Patients: Average age of 37 years

Higher in Diabetic Patients: Hypertension, cardiovascular disease, chronic lung disease, immune deficiency, and hyperlipidemia

Increased Symptoms: Fever, cough, shortness of breath, headache

Higher odds of fever, cough, shortness of breath, and headache compared to non-diabetic patients

Diabetic Mortality Rate: 14.3%

Proportion of Deaths in Diabetics: 28.3% of COVID-19-related deaths occurred in diabetic patients

Public Health Challenge: Diabetes significantly increases mortality from COVID-19, highlighting the need for targeted prevention and treatment strategies for diabetic patients

Makker et al., 2021 [30]

Not specified (Single-center study)

Retrospective observational study

733

Patients were categorized into three groups: control (non-diabetic), prediabetes, and type-2 diabetes

Key stratification at 55 years Mortality and mechanical ventilation use compared among younger (< 55 years) and older (≥ 55 years) patients

Type-2 diabetes, prediabetes, newly diagnosed vs. previously diagnosed diabetes

Not detailed; focus on clinical outcomes such as mortality and mechanical ventilation

Older patients (≥ 55 years): No significant difference in mortality or mechanical ventilation among control, prediabetes, and type-2 diabetes groups

Younger patients (< 55 years): Higher mortality in type-2 diabetes group (27%) compared to control (9%) and prediabetes (12.5%)

Newly diagnosed type-2 diabetes: Lower mortality (18%) compared to previously known type-2 diabetes patients (40%)

Prediabetes: Outcomes similar to the control group

Admission hyperglycemia is associated with higher mortality regardless of diabetes status

Kania et al., 2023 [31]

Poland

Retrospective study

5,191

The study included 1,364 diabetic patients (26.3%) and compared them with non-diabetic patients

Diabetic patients were older (median age 70 years) compared to non-diabetics (median age 62 years)

Diabetic patients had higher rates of comorbidities such as heart failure and chronic kidney disease Risk factors associated with higher mortality included age > 65 years, glycemia > 10 mmol/L, elevated CRP and D-dimer levels, and prehospital use of insulin and loop diuretics

The study focused on outcomes rather than specific symptoms

Diabetic patients had a higher mortality rate (26.2% vs. 15.7%, p < 0.001) and longer hospital stays. Factors contributing to lower mortality included the in-hospital use of statins, thiazide diuretics, and calcium channel blockers

Diabetic patients required more intensive care, including higher rates of ICU admission (15.7% vs. 11.0%) and mechanical ventilation (15.5% vs. 11.3%). They also had longer hospital stays compared to non-diabetics

Abed et al., 2022 [32]

Algeria

Observational study

285

48.80% of the patients in the sample had diabetes

The rest had no mention of diabetes, implying non-diabetic or unspecified status

Average age of diabetic patients: 62.53 ± 16.65 years

High CRP levels in 95.7%

Hyperglycemia in 64%

Hyperleukocytosis in 26.6%

Elevated D-dimer in 56%

Hypoprothrombinemia in 21.6%

High urea levels in 36.7%

Hypo-creatinemia in 12%

Elevated ASAL and ALAT in 28.8% and 26.6%, respectively

Oxygen desaturation in 64.7%

Important or critical pulmonary affliction in 28.8% and 18.7%, respectively

Mortality rate among diabetic patients: 22.3%

The report does not specify the exact number of patients alive or recovered, only the mortality rate

The study emphasizes the need for improved care for diabetic patients due to high infection rates, biological abnormalities, and mortality

Al-Salameh et al., 2021 [33]

France

Retrospective cohort study

432

115 patients with diabetes (26.6%), 318 patients without diabetes (73.4%)

Median age of 72 years

Diabetes, older age associated with higher mortality; diabetes associated with longer hospital stay and higher ICU admission

Not detailed, focus on clinical outcomes such as ICU admission and mortality

Diabetes was not significantly associated with mortality (HR: 0.73; 95% CI: 0.40–1.34), but was associated with ICU admission (OR: 2.06; 95% CI: 1.09–3.92, P =.027)

Diabetes was associated with a greater risk of ICU admission and a longer hospital stay; age was negatively associated with ICU admission and positively associated with mortality

You et al., 2020 [34]

Korea

Retrospective cohort study

5,473

495 patients with type 2 diabetes, 4,978 patients without diabetes

Not specified, but adjustment for age was made in the analysis

Comorbidities adjusted for in the analysis, higher likelihood of ICU admission for diabetes patients

Not explicitly detailed, but focus on ICU admission, in-hospital mortality, and clinical outcomes

Higher in-hospital mortality for diabetes patients (P < 0.0001); adjusted odds ratio for mortality was 1.90 (95% CI, 1.13 to 3.21, P = 0.0161)

Higher odds of ICU admission for diabetes patients (adjusted OR 1.59, 95% CI 1.02 to 2.49, P = 0.0416); no significant difference in ventilator use, oxygen therapy, antibiotics, antiviral drugs, antipyretics, or incidence of pneumonia after adjustment

Badedi et al.,2022 [35]

Saudi Arabia

Retrospective cohort study

412

The study included patients with type 2 diabetes mellitus (T2DM) compared to those without T2DM

Not specified, but the study focused on adult patients

COVID-19 patients with T2DM had increased blood glucose levels, requiring higher insulin doses. They were also more likely to have severe complications, such as an oxygen saturation of ≤ 90%, and were more frequently admitted to the intensive care unit (11% vs. 5%)

Most patients with T2DM exhibited clinical COVID-19 symptoms (91%), while 9% were asymptomatic. Those with mild symptoms often self-isolated at home (80%)

Mortality was higher in COVID-19 patients with T2DM (9%) compared to those without T2DM (1%)

COVID-19 patients with T2DM required more intensive care and increased insulin doses during their hospital stay. The disease duration was also longer for T2DM patients compared to non-diabetic patients (10.7 days vs. 8.3 days)

Kantroo et al., 2021 [36]

India

Retrospective study

1,192

26.8% of the patients had diabetes mellitus (DM)

Increased age was associated with higher mortality

The study identified several comorbidities significantly associated with mortality, including chronic kidney disease (CKD), coronary artery disease (CAD), stroke, and cancer. CAD, CKD, and cancer were independent predictors of mortality

Patients who presented with breathlessness, low oxygen saturation (SpO2), extensive lung involvement on chest X-ray (CXR), and an elevated absolute neutrophil count/absolute lymphocyte count (ANC/ALC) ratio were more likely to experience severe outcomes

The overall mortality rate was 6.1%, and it was higher in patients with diabetes (10.7%)

Early triaging and aggressive therapy were recommended to optimize clinical outcomes for patients with comorbidities such as DM, hypertension, CAD, CKD, and cancer