The Role of Diagnostic Management in COVID-19 Screening of Asymptomatic Patients Admitted for Elective Surgery

Discussion

Strategies of preoperative diagnostic screening for a potential COVID19 infection in patients qualifying for an elective surgery are under dispute. Qualifying an infected patient for an elective surgery who presents very few and weak symptoms or is asymptomatic is of the greatest concern because of the risk of transmission of infection to other patients or personnel. One of the solutions adopted by countries with a relatively high SARS-CoV-2 infection rate is screening with RT-PCR test at admission, irrespectively of admission type (emergency or elective) (2, 3).

RT-PCR testing of the material from the nasopharyngeal swab is a first-line diagnostic technique for COVID-19 infection (3-5). The technique is useful for infection disease monitoring and as a criterion for hospital discharge or transfer. However, a high false-negative rate is common, among others, due to the time of sample collection and disease course mismatch. Therefore, two consecutive RT-PCR tests over 24-72 hours are recommended to minimize the false-negative rate (1).

Some countries have adopted an alternative strategy, which complements the RT-PCR test with a chest X-ray or a chest CT scan to verify the patient’s clinical status (2, 6). Blood biomarkers such as C-reactive protein, lymphocyte count, low procalcitonin, elevated interleukin-6 and -10 levels may also prove helpful (1, 5). Yet Polish guidelines restrict RT-PCR test to symptomatic patients only and recommend chest imaging with X-ray as a modality of first choice in cases of confirmed infection and symptoms suggesting lung involvement (5).

The lack of unequivocal guidelines for a preoperative SARS-Cov-2 prophylactic strategy for low-risk patients have led our team of anesthesiologists, surgeons and epidemiologists to define, in the first months of the pandemic, measures for a rational evaluation of perioperative infection risk. Hence, this study presents the results of chest CT and the blood differential test performed routinely for all patients admitted to our clinic for elective surgery. This diagnostic algorithm was adopted taking into consideration the high infection rate in Poland in the first quarter of 2020 and was in line with the guidelines of the Agency for Health Technology Assessment and Tariff System (AOTMiT), which limit the use of RT-PCR to high-risk patients (5).

Nevertheless, routine imaging studies, chest CT especially, in patients with low risk of infection remains quite controversial. Polish guidelines limit chest imaging only to patients with symptomatic COVID-19 (5, 6). Similarly, the Royal College of Radiologists does not recommend the routine preoperative chest CT scan at all. In asymptomatic patients with a positive RT-PCR result, the scan may be normal, whereas it can be falsely negative in 20% of symptomatic patients (7). On the other hand, when it is not possible to perform an RT-PCR test, a chest X-ray is the modality of choice in the diagnostics of a patient suspected of having COVID-19, particularly when other lung pathologies are suspected (4, 8, 9). However, low sensitivity (69%) makes chest X-rays poor in excluding COVID-19, while detecting infection must be supported and justified clinically (8-10).

The results of our study are in line with the abovementioned existing recommendations and confirm the necessity of clinical justification for chest imaging. Routine chest CT screening for COVID-19 changes in asymptomatic patients showed no benefits. It may be useful providing the clinical symptoms or past medical history suggest lung pathology, as shown by the higher rate of abnormal chest CT scans being observed in a group admitted in an emergency setting. Since a drop in lymphocyte count and increased leukocytes were not uncommon, A blood differential test has very limited value in COVID-19 screening. However, a blood smear may be considered helpful considering that lymphopenia is often present in patients with viral infections (11, 12).

In conclusion, the question of an optimal strategy for COVID-19 screening of patients admitted for elective surgery remains open. Laboratory blood tests, imaging and molecular COVID-19 diagnostic tests are all dedicated to symptomatic patients, which leaves asymptomatic patients as source of a potential horizontal transmission. Moreover, COVID-19 vaccination does not solve this problem as some patients remain unvaccinated or do not respond properly to vaccination. Laboratory blood tests such as blood smear may be helpful but are far from sufficient for an effective screening of potentially infected asymptomatic patients preoperatively. The need for an optimal diagnostic algorithm that would effectively limit the risk of SARS-CoV-2 transmission in medical centers is even more imperative in times of epidemiological stabilization.