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PSI vs CURB-65 score: Which is better at predicting 30-day mortality in COVID-19 patients?

M3 India Newsdesk Aug 06, 2020

A retrospective study conducted recently assessed the abilities of CURB-65 and the pneumonia severity index (PSI) to predict 30-day mortality in hospitalised patients with COVID-19. The study found that PSI is a more powerful tool than CURB-65 in predicting mortality and hence PSI is recommended to risk stratify patients during hospitalisation.

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The novel coronavirus disease 2019 (COVID-19) outbreak has claimed the lives of many across the world. Looking at the rapid phase at which the virus spreads, quick access to the right medical care can be critical.

Respiratory failure is the main cause of mortality in patients with COVID-19. Other complications which lead to death include myocardial injury, kidney or liver injury, and multi-organ dysfunction.

Several prognostic factors such as older age, male gender, presence of comorbidities, and smoking may render a person more susceptible to the deadly disease. Deceased patients are also more likely to have had leukocytosis, lymphopenia, higher levels of lactate dehydrogenase, C-reactive protein (CRP), interleukin (IL)-6, troponin, and D-Dimer, and an elevated neutrophil-to-lymphocyte ratio.

In order to predict the 30-day mortality in patients with COVID-19, a retrospective study was performed in a pandemic hospital in Istanbul, Turkey. The study included 681 laboratory-confirmed patients with COVID-19. The objective was to analyse the usefulness of CURB-65 and the pneumonia severity index (PSI) in predicting mortality and to identify factors associated with higher mortality.


CURB-65 and the pneumonia severity index (PSI)

CURB-65 and the pneumonia severity index (PSI) are popular tools to predict 30-day mortality in community-acquired pneumonia.

Pneumonia Severity Index (PSI) is a scoring system (see table below for detailed description), comprising of clinical and laboratory parameters. Based on the total score, patients can be categorised into 5 risk classes from I to V.

Pneumonia severity index

Patient Age Score
Male Age
Female Age-10
Long-term care facility resident +10
Accompanying Disease Score
Neoplastic disease +30
Liver disease +20
Congestive heart failure +10
Cerebrovascular disease +10
Chronic kidney disease +10
Symptoms at diagnosis Score
Acute psychosis +20
Breathing rate ≥30/min +20
Systolic pressure <90 mmHg +15
Heart rate ≥125/min +10
Laboratory Measurements Score
Arterial blood pH <7.73 +30
Blood urea nitrogen ≥30 mg/dL +20
Serum sodium <130 meq/L +20
Serum glucose >250 mg/dL +10
Haemoglobin <9 mg/dL +10
Partial pressure of oxygen <60 mmHg +10
Pleural effusion +10

PSI Group PSI Score Risk
I Age <50, none from comorbidities, physical and laboratory findings Low risk
II ≤70 Low risk
III 71-90 Low risk
IV 91-130 High risk
V >130 High risk

CURB-65 Scoring System

CURB-65 (Confusion, Urea, Respiratory rate, Blood pressure plus age ≥ 65 years) is another severity score for CAP management. The CURB-65 comprises 5 variables (as depicted in the table below), attributing 1 point for each item. As per the CURB-65 scoring system, patients are divided into low, moderate and high risk.

Clinical Features Points
Confusion 1
Urea >7 mmol/L 1
Respiratory rate ≥30 1
Systolic blood pressure ≤90 mmHg or diastolic blood pressure ≤60 mmHg 1
Age over 65 years 1
CURB-65 Score Risk
0-1 Low risk
≥2 Moderate and high risk

Study details

The study retrospectively enrolled 681 patients who had been diagnosed with COVID-19 pneumonia between April 2, 2020, and May 1, 2020. Data on characteristics, vital signs, and laboratory parameters were recorded from electronic medical records.

In the enrolled patients,

  • The most common comorbidity was hypertension, followed by diabetes mellitus, asthma, chronic obstructive lung disease, ischemic heart disease, hyperlipidaemia, chronic renal disease, and congestive heart failure
  • The most common clinical presentations were fever (32.5%) and respiratory tract symptoms, including cough (71.2%) and dyspnoea (27.3%)

The main study outcome was 30-day mortality, defined as documented death from any cause during hospitalisation or within 30 days of admission to our emergency department. The CURB-65 and PSI scores at hospital admission were calculated as depicted in the table.

  • CURB-65 scores range from 0 to 4. A score of 0–1 indicated a low risk for mortality, whereas scores of 2 or higher are associated with higher mortality.
  • PSI scores are classified into groups I, II, III, IV, and V. Patients were stratified into two levels of risk: low risk (groups I–III) and high risk (groups IV–V).

Key findings

The 30-day mortality rate in the study was found to be 8%. Deceased patients were older, more hypoxic, tachycardic, tachypneic, and hypotensive at admission and were more likely to have at least one comorbidity. With respect to laboratory parameters, the deceased patients had higher neutrophil counts, and higher levels of blood urea nitrogen, ferritin, CRP, and troponin, as well as lower lymphocyte counts.

In the study population, the PSI ≥ 4 group showed better sensitivity (80% vs 73%) and specificity (89% vs 85%) in predicting death compared with a CURB-65 score of ≥ 2.

PSI

  • 182 patients (26.7%) were in group I - There were no deaths among the patients in group I
  • 249 patients (36.6%) were in group II - The mortality rate was 2% in group II
  • 136 patients (20%) were in group III - The mortality rate was 4.4% in group III
  • 82 patients (12%) were in group IV- The mortality rate was 28% in group IV
  • 31 patients (4.7%) were in group V- The mortality rate was, and 65.6% in group V

CURB-65

  • 550 (80.8%) patients had a CURB-65 score of 0 or 1
    • Of these, 15 patients (2.7%) died within 30 days
  • 131 patients (19.2%) had a CURB-65 score of ≥2
    • Of these, 40 patients (30.5%) died within 30 days

Other variables in predicting 30-day mortality in COVID-19 pneumonia

Apart from PSI and CURB-65, the levels of ferritin, CRP, and troponin, and lymphocyte count, were also associated with 30-day mortality. However, of these variables, only elevated CRP values (p < 0.001) were found to be significantly associated. Additionally, the study found that the addition of CRP levels to PSI did not improve the performance of PSI in predicting mortality (p = 0.29).


Key takeaways

In conclusion, the study showed that PSI is a powerful tool for predicting mortality in patients with COVID-19. It performed significantly better than CURB-65, while the addition of CRP levels to PSI scale did not improve the performance of PSI. During the outbreak, PSI can help physicians to stratify patients on admission.


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