Evaluation of Routine Blood Tests for Diagnosis of Suspected Coronavirus Disease 2019

Real-time reverse transcription polymerase chain reaction assay (RT-PCR) is the gold standard for diagnosis of coronavirus disease 2019 (COVID-19); however, it is not universally available and may have limitations in response times. The aim was to evaluate the routine blood tests for diagnosis of COVID-19, determining the diagnostic accuracy of blood biomarkers to differentiate between patients with and without COVID-19.

Clinical charts, nursing records, laboratory findings, and chest x-rays from adult patients with clinical suspicion of COVID-19 (fever, cough and/or dyspnea) at hospital admission were reviewed. Patients were classified into two groups according to RT-PCR COVID-19: positive (COVID-19) or negative (NON-COVID-19). Diagnostic accuracy was determined by analyzing receiver operating characteristic (ROC) curve, calculating the area under the ROC curve (AUC) and the cutoff value. In order to reduce the number of false positives, the cutoff value with a specificity of 80% was considered.

Two hundred three patients (101 females, 102 males) with ages between 18 and 96 years (mean = 61.3) were studied. Ninety-four were COVID-19 and 109 were NON-COVID-19. Plasma ferritin level was the most accurate biomarker (AUC = 0.847 and 0.804 in women and men, respectively). The following diagnostic criteria for suspected COVID-19 were established with biomarker cutoff values to differentiate between COVID-19 and NON-COVID-19 patients: lymphocytes ≤ 1.0 x 109/L; eosinophils ≤ 0.02 x 109/L; ferritin > 125% of upper reference limit (URL); LDH > 125% of URL; hsCRP > 80 mg/L; and D-dimer > 1.2 mg/L. Sensitivity was 66%, 64% 62%, 46%, 43%, and 33% for ferritin, eosinophils, LDH, hsCRP, lymphocytes, and D-dimer, respectively. Of those determined to be COVID-19 patients, 91% met one or more of the diagnostic criteria with these blood biomarkers, and of the NON-COVID-19 patients, 47% did not met any diagnostic criteria.

Blood counts of lymphocytes and eosinophils, and plasma levels of D-dimer, LDH, hsCRP, and ferritin can be used to differentiate patients with and without COVID-19 and as a tool for diagnosis of suspected COVID-19 in adult patients at hospital admission.