Hi I'm Dr. Joseph Becker. Hi I'm Dr. Joshua Stein. We're physicians in the emergency department at
Stanford University and we're here to talk to you about assessing the dyspneic patient from the
standpoint of laboratory diagnostic testing. In this talk we're going to discuss the different
diagnostic tests that can be used by physicians in evaluating patients with Covid-19. Some tests
may indicate that a patient has a worse prognosis and therefore may need a higher level of care. Your
clinical assessment of a patient as being sick is always more important than diagnostic testing.
If a patient is breathing fast, is hypoxic or is confused, normal laboratory tests do
not mean that that patient is not sick. However, laboratory testing and imaging can be used to
indicate that a patient has the potential to get worse and may need closer clinical monitoring or
treatment. The primary tests for diagnosing acute Sars-Cov-2 infection or Covid-19 disease
is PCR of a nasopharyngeal swab. PCR aims to identify the actual genetic material of the virus.
The effectiveness of the test depends on the collection of an adequate sample.
There is another test called the nucleic acid amplification test or NAAT. The NAAT
test is also looking for genetic material from the virus but it is more easily performed and
yields results more rapidly than the PCR test. When obtaining a nasopharyngeal swab, the swab
should reach a depth equal to the distance from the nostrils to the outer opening of the ear.
Insert the swab parallel to the palate, not up, until resistance is encountered or you reach the
proper depth leave the swab in place for up to 10 seconds then rotate the swab and remove.
If the swab is unable to be passed to the appropriate depth on that nostril use the same swab to obtain
the sample from the other nostril. Another common type of swab is an oropharyngeal swab.
When obtaining this swab, rub the tonsillar pillars and post your oral pharynx vigorously for several
seconds. Finally, some tests utilize a saliva sample which may be obtained via a swab or a
sputum sample. It is important to collect samples consistently using the same approach with every
patient in accordance with the directions of that particular test. Some tests report low sensitivity
rates thus if a patient who is highly suspected of having Covid-19 tests negative, repeat testing
may be necessary before Covid-19 can be ruled out and that patient removed from isolation.
However, these tests are usually very specific - if a test is positive, it most of the time can
be trusted. In patients with severe pneumonia lower respiratory samples may more reliably detect virus.
These tests indicate the presence of genetic material they do not necessarily indicate the
presence of infectious virus particles and patients may continue to test positive for
weeks after recovering from Covid-19. A positive test after clinical recovery and completion of an
isolation protocol does not necessarily indicate transmissibility. There are also tests that look
for proteins found in the Sars-Cov-2 virus. These tests are called antigen tests. Many different
versions of these tests exist. These tests vary widely as to their sensitivity and specificity
however one advantage of these tests is that they are very rapid and much more easily performed
and do not require additional laboratory training or techniques. When using a test
it is incredibly important to know which tests you have as well as its testing characteristics.
Antibody testing may be performed of the saliva or the blood and the presence of antibodies indicates
prior infection with the virus these assays may test for igg or igm antibodies. These both appear 7
to 14 days after infection however igm antibodies disappear by seven weeks after infection, whereas,
igg antibodies can last for several months. Antibodies also appear after administering
the Covid-19 vaccine. Although less common, it is possible to be infected with Coronavirus
after prior Covid infection or vaccination. Symptoms are usually mild in these cases. Because
of this healthcare providers who test positive for igm or igg for Sars-Cov-2 or who have already
been vaccinated should still wear appropriate PPE when caring for patients with coronavirus.
You can also consider testing for other common diseases that are prevalent in your area
these diseases may include influenza, malaria, dengue, tuberculosis or hiv.
Additionally, patients can still have disease processes like cholecystitis, appendicitis,
or bacterial pneumonia. If you would have considered those diagnoses prior to the pandemic
you should still consider them now and obtain appropriate diagnostic testing and imaging
of your patient. Being able to interpret blood gas results is an important part of medicine.
This slide represents a useful tool in interpreting acid-base abnormalities in patients.
We will not go into great depth at this point discussing the elements of blood gas evaluation.
In Covid-19 patients the blood gas abnormality most commonly noted is hypoxemia.
Additionally, patients may also show evidence of a metabolic acidosis from shock. This is
often associated with an elevated lactic acid level as an indicator of poor tissue perfusion.
This level can be trended over time to evaluate the resuscitation of the patient.
However, if a patient is noted to have a high carbon dioxide level
another explanation should be considered as this is not typical for Covid-19 alone.
Additionally. remember that a normal ph but an abnormal carbon dioxide level or
bicarbonate level indicate that a patient has a compensated or mixed acid-base disorder that
needs to be further evaluated. Many lab tests have been associated with a poor prognosis
for Covid-19 infections. However many of the tests that have been identified in the literature
may not be available in smaller hospitals or sites with limited resources. Use whatever you have
available. If a test takes many days to results it will not be clinically useful for prognosis.
One of the first markers identified was lymphopenia or low lymphocyte count. If you have
the ability to do a cbc with a differential you'll be able to identify this abnormality. Additionally a
poor prognosis has been associated with inflammatory markers that are very elevated such
as c-reactive protein and ferritin. Esr is also elevated in 85 percent of patients with Covid-19.
Similarly there seems to be a strong tendency for patients with Covid-19 to have clotting
disorders. This often leads to inappropriate clot formation and complications such as
stroke or myocardial infarction. Laboratory studies such as d-dimer and fibrinogen
are predictors of worse outcomes in patients with Covid-19. Coagulation tests like the ptt, the pt,
and the inr should also be obtained as patients may require anticoagulation.
One of the additional causes of mortality seems to be from cardiogenic shock and arrhythmias.
Troponin or other cardiac biomarkers are important to evaluate for cardiac damage either
from focal myocardial ischemia, systemic shock, or myocardial inflammation such as myocarditis.
And as is the case with many ill patients it is always a good idea to check general
laboratory tests. Renal function as assessed by the creatinine and urea nitrogen tests
is critical in aiding decision making regarding perfusion as well as patient volume status.
Electrolytes are very important to check in any critically ill patient as abnormalities
of potassium sodium calcium or magnesium could lead to complications and worsened outcomes.
Liver function tests may be elevated in patients with Covid-19 and can be a predictor of poor outcome.
Elevated liver function tests can also predict the presence of drug toxicity or infarction.
Low albumin has also been associated with a poor prognosis in Covid-19 disease. All women of
childbearing age should further have a pregnancy test checked as this can affect medication
or imaging choices and pregnancy has been associated with increased mortality in Covid-19.
In early Covid-19 the ecg is often normal- like this ecg or looks similar to the patient's prior ecg.
Myocardial inflammation relating to myocarditis may not show any significant ecg findings
but can still cause significant mortality. In the absence of ecg findings the troponin or
other cardiac biomarker is often elevated in cases of myocarditis.
The ecg may alternatively demonstrate signs of focal ischemia related to an individual coronary
vessel blockage or changes in the interval such as qtc prolongation. As some deaths from Covid-19
have been associated with cardiogenic shock and arrhythmia it is important to keep ill patients
on a cardiac monitor if possible. Many of these laboratory tests have been used in conjunction
with vital signs and past medical history to develop various risk score calculations.
The best performing risk score calculation so far is the 4c score. The 4c score can help predict
mortality in patients with Covid-19 and is easily calculatable and accessible online. It requires
the bun or creatinine and the crp. Do not rely solely on any risk calculator and always using
can use them in conjunction with your clinical assessment of the patient.
In summary, understand how to administer the type of Covid test used at your institution and its test characteristics.
Consider obtaining laboratory tests that are commonly abnormal and predictive of worse
outcomes in Covid-19. Your clinical assessment of a patient as being sick is always more important
than any diagnostic testing. Focus on stabilizing a patient first. An exact diagnosis initially is less
important. Focus the initial testing on evaluating for life-threatening but treatable problems.
Remember that in a pandemic many people may have Covid-19 but they may also have other
medical problems that require specific treatment consider that patients may have other illnesses
such as malaria, bacterial pneumonia, or appendicitis while also having Covid-19.
This concludes this presentation. Thank you all for your time and attention.