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Case Study on the Challenges of COVID-19 Diagnostics

Learn more from a case study of a COVID-19 patient who may be presenting with sepsis.
Illustration of coronavirus viruses
© Photo by CDC on Unsplash

The emergence of COVID-19 has presented new clinical challenges, and we will now present two case studies that highlight the challenges in diagnosing infection.


The patient was a 62-year-old male, with a patient history that included hypertension and type 2 diabetes mellitus. He was admitted to the hospital after presenting with a cough, shortness of breath, and rigors for five days.

Initial Measurements

On admission to the hospital the patient had an oxygen requirement of 6 L/min (litres per minute) to maintain an oxygen saturation (SpO2) of over 92%. In order to understand the next steps, several measurements were taken:

  • Temperature = 38.9°C
  • CRP = 45
  • WCC = 12.7, lymphocytes = 0.4, neutrophils = 8.9, PCT = 0.04
  • Urea and electrolytes (U&Es) and liver function tests (LFTs) were found to be normal
  • D-dimer = 2574, ferritin = 1123, lactate dehydrogenase (LDH) = 342
  • Arterial blood gas (ABG) = pH 7.43, PaO2 = 10.7, HCO3 = 22, BE = 0.1, lactate = 1.2

The patient was given a chest X-ray and this showed bilateral infiltrates. He also tested positive for COVID-19. Overall his vitals were stable. His heart rate was 100 beats per minute with blood pressure 145/80. It was noted that the patient was passing water and felt thirsty.

After the initial admissions measurements, the next step which should be carried out is to consider the Sepsis Six. Sepsis is defined as a dysregulated host response leading to organ dysfunction, and in this case, respiratory dysfunction; Sepsis Six advocates for early antibiotic intervention in case the offending pathogen is bacterial.


COVID-19 pneumonitis can result in viral sepsis, and studies by Lansbury et al and Adler et al suggest that the prevalence of concomitant bacterial infection in COVID-19 pneumonitis is low. Despite this, the current national guidance (in the UK) suggests the use of antibiotics for severe COVID-19 pneumonitis, and the cessation of antimicrobials is left to the clinician’s discretion.

The overuse and misuse of antibiotics is a continuing issue, and so it is important to consider both traditional and novel diagnostics of bacterial infection to reduce unnecessary antibiotic exposure. Recent reports suggest low rates of pneumococcal and legionella co-infections on hospital admission, with the most positive sputum samples colonised by oropharyngeal flora.

Procalcitonin could be a useful biomarker to aid antibiotic stewardship and use of the previously established thresholds for starting and stopping antibiotics could be used.

In the presented case, the pre-test probability of severe bacterial co-infection is low, aided by the PCT result, and it would not be appropriate to start empirical antibiotics, unless other microbiology testing suggests otherwise.

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Procalcitonin: PCT as a Biomarker for Antimicrobial Stewardship

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