Apr 29, 2020
Contributor: Don Stader, MD
- COVID-19 is diagnosed
with a nasopharyngeal swab (q-tip). This unfortunately can be
painful, but if the swab doesn’t go deep into the nasal cavity the
sample can be inadequate leading to false negatives (missed
- The sensitivity of the COVID-19
RT PCR test is low, ranging from 66-80% in various studies. Another
study has shown 23% of patients who initially tested negative but
had COVID-19 symptoms will test positive when re-tested. So test
highly suspicious patients twice.
has shown to have an effect on CBC. White blood cell counts are
often normal (no leukocytosis), but there is often lymphopenia, or
low lymphocytes, and thrombocytopenia. Interestingly, low platelets
have appeared to have prognostic value in that lower platelets
often indicate worse patient outcomes.
- Coagulation studies are showing very elevated
D-Dimers which has sparked the debate as to whether COVID-19 causes
a hypercoagulable state. The increased incidence of MI/heart
attacks and strokes in COVID patients supports this
D-Dimers can help point towards a diagnosis of pulmonary embolism,
in the setting of highly likely COVID-19 infections, getting a CTA
looking for a PE is probably unnecessary unless there’s also
suspicion for PE.
- C-reactive protein (CRP) and procalcitonin are
two common inflammatory markers. A CRP can help indicate how sick a
patient is and procalcitonin can help determine if the infection is
bacterial or viral in nature.
levels are often elevated in COVID patients, and studies are
showing a high CRP is linked to worse patient
- Elevations in procalcitonin can be used to see
if there’s a concomitant bacterial infection, meaning patients need
antibiotics in addition to supportive care for the
season is coming to a close, but data has shown a 5-10%
co-infection rate of COVID-19 with influenza. As expected patient
outcomes have been worse in those with both
1) Farkas, Josh. “COVID-19.”
Project, 21 Apr. 2020,
2) Guan W. et al. Clinical Characteristics of Coronavirus
Disease 2019 in China. February 28, 2020, updated on March 6,
2020, at NEJM.org. DOI: 10.1056/NEJMoa2002032
3)Young BE, Ong SWX,
Kalimuddin S, et al. Epidemiologic Features and Clinical Course of
Patients Infected With SARS-CoV-2 in Singapore.
4) Wang M.
et al. Clinical diagnosis of 8274 samples with
2019-novel coronavirus in Wuhan. medRxiv 2020.02.12.20022327; doi:
Summarized by Jackson Roos,
MS4 | Edited by Erik Verzemnieks, MD