COVID-19 Recognition: Using Investigations to Predict Risk

In low and middle income countries, local capacity of RT-PCR tests, for COVID-19 diagnosis, may not be sufficient to test and screen everyone presenting with suspected COVID-19. Ideally, lower-cost and readily available alternatives could help low and middle-income countries with making their COVID-19 diagnoses during this pandemic.

Currently, rapid serological tests are not validated to be used outside of the research setting and antigen tests for COVID-19 are not adequately specific and still require follow-up with a formal RT-PCR test to confirm a diagnosis.

“WHO does not recommend the use of antibody-detecting rapid diagnostic tests for patient care but encourages the continuation of work to establish their usefulness in disease surveillance and epidemiologic research.”

World Health Organisation, Excerpt from Scientific Brief published 8 April 2020

The British Medical Journal have published a list of 1st Investigations to Order when assessing a patient with suspected COVID-19.

Table of investigations from BMJ COVID-19
From BMJ: 1st Investigations to Order

Here we will discuss the other investigations which can be used when assessing a patient with suspected and summarise the evidence for predicting the risk of a COVID-19 infection.

History taking:

In addition to eliciting the onset, severity and timing of COVID-19 signs and symptoms, it is important to determine if your patient is in a high-risk group (e.g over 60 years old, underlying comorbidities, immunocompromised) [1,2,7]

COVID-19 infection severity

Clinical Observations:

"Silent Hypoxia"
Studies have reported that COVID-19 infection can present as “silent hypoxia” which refers to oxygen saturations (on oximetry) much lower than what one would expect from the patient’s work of breathing. This conclusion was drawn based on data and observations from cases series of confirmed COVID-19 patients who presenting to emergency services [2,3]. 

A systematic review and meta-analysis by Rodriguez-Morales et al. (2020) [4], which included data from China and Australia, concluded that 32.8% presented with acute respiratory distress syndrome (ARDS), 6.2% with shock.


Arterial Blood Gas:

Arterial blood gases (ABG) used worldwide to assess oxygenation and degree of respiratory or metabolic acidosis/alkalosis in an unwell patient. Although this has been used in the monitoring of patients with COVID-19, the changes in ABG in a deteriorating patient is not specific or sensitive for COVID-19 infection.

Additional Blood tests:

COVID-19 is associated with systemic and multi-organ effects, however blood biomarkers have been more useful in monitoring than the diagnosis of ongoing infection. [2,4]

From Rodriguez-Morales et al. (2020) [4], the following results were most prevalent in COVID-19 cases:

-        Decreased albumin (75.8%)

-        High C-reactive protein (58.3%)

-        High lactate dehydrogenase (LDH) (57.0%)

-        Lymphopenia (43.1%)

-        High erythrocyte sedimentation rate (ESR) (41.8%)

Imaging: CXR vs CT-chest

High resolution CT-chest imaging has been used in the diagnosis and assessment of COVID-19 infection. However this is modality may not be readily available and is an expensive resource in many low and middle-income countries.

In addition, RT-PCR for COVID-19 is still more sensitive at screening than CT-chest [5,6]. Across published case series, the most common feature on plain chest radiograph (CXR) is consolidation, and peak CXR changes may appear 10-12 days from symptom onset, which can also be bilateral. [6]

However, caution should be taken when interpreting CXR and CT-imaging, as the changes described in literature are not pathognomonic for COVID-19 and there is significant overlap with other viral and non-viral pneumonias (e.g. H1N1 influenza, cytomegalovirus pneumonia, atypical pneumonia).


Further Reading:

Signs and Symptoms of COVID-19

COVID-19 and Comorbidities (coming soon)

COVID-19 and Prognosis (coming soon)


  1. CDC, 14 May 2020, Groups at Higher Risk for Severe Illness, URL: (Accessed 24/5/2020)

  2. Xie J, Tong Z, Guan X, et al. Critical care crisis and some recommendations during the COVID-19 epidemic in China. Intensive Care Med. 2020 May;46(5):837-40

  3. Gattinoni L. et al. COVID-19 pneumonia: different respiratory treatment for different phenotypes? (2020) Intensive Care Medicine; DOI: 10.1007/s00134-020-06033-2

  4. Rodriguez-Morales AJ, Cardona-Ospina JA, Gutiérrez-Ocampo E, et al. Clinical, laboratory and imaging features of COVID-19: A systematic review and meta-analysis. Travel Med Infect Dis. 2020;34:101623. doi:10.1016/j.tmaid.2020.101623

  5. Fang Y, Zhang H, Xie J, Lin M, Ying L, Pang P, Ji W. Sensitivity of Chest CT for COVID-19: Comparison to RT-PCR. (2020) Radiology. doi:10.1148/radiol.2020200432

  6. Wong HYF, Lam HYS, Fong AH, et al. Frequency and Distribution of Chest Radiographic Findings in COVID-19 Positive Patients [published online ahead of print, 2019 Mar 27]. Radiology. 2019;201160. doi:10.1148/radiol.2020201160

  7. Jordan RE, Adab P, Cheng KK. Covid-19: risk factors for severe disease and death. BMJ. 2020;368:m1198. Published 2020 Mar 26. doi:10.1136/bmj.m1198

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