Absolute Lymphocytes, Ferritin, C-Reactive Protein, and Lactate Dehydrogenase Predict Early Invasive Ventilation in Patients With COVID-19

Salvador Payán-Pernía, MD; Lucía Gómez Pérez, MD; Ángel F. Remacha Sevilla, MD, PhD; Jordi Sierra Gil, MD, PhD; Silvana Novelli Canales, MD, PhD


Lab Med. 2021;52(2):141-145. 

In This Article


This retrospective observational study was performed at Hospital de la Santa Creu i Sant Pau, a first-level hospital in Barcelona, Spain. The study was conducted according to the Declaration of Helsinki and approved by the institutional ethics committee. For patient enrollment, all consecutive blood tests that included ferritin between March 15, 2020 and April 6, 2020 were reviewed. In this way, patients diagnosed with COVID-19 in whom serum ferritin, ALC, platelet count, CRP, and LDH had been analyzed at admission were selected. In all patients, these parameters were determined in the same sample or with a maximum time difference of 24 hours. We assessed ALC on a Sysmex XN-10 (Sysmex Corporation, Kobe, Japan) analyzer. Serum ferritin was measured on an Architect c16000 System (Abbott Laboratories, IL) using a 2-step chemiluminescent microparticle immunoassay. We determined CRP and LDH in serum using the Alinity c system (Abbot Laboratories, IL), the former using a particle-enhanced immunoturbidimetric assay, the latter using spectrophotometry.

One hundred sixty patients aged 23 to 75 years were recruited. Informed consent was obtained from all participants. One hundred fifty-eight patients had a laboratory-confirmed SARS-CoV-2 infection according to World Health Organization guidance:[10] a positive result of real-time reverse-transcriptase polymerase chain reaction (RT-PCR) assay of a nasopharyngeal swab. In 2 patients, RT-PCR was negative and the diagnosis of COVID-19 was made presumptively based on a compatible clinical presentation and an exposure risk. Patients who received tocilizumab, a monoclonal antibody against IL-6, at any time during their hospital stay were excluded for the study because this agent has been associated with a decrease in CRP and ferritin levels.[11] Patients with active neoplasia were also excluded because of iron overload.

Demographic, clinical, laboratory, and outcome data were extracted from electronic medical records. An image on chest radiograph was considered typical of COVID-19 in the presence of consolidation and ground-glass opacities, with bilateral, peripheral, and lower lung zone distributions. All patients were evaluated until death or hospital discharge.

Descriptive analyses of the variables were expressed as mean (range) or the number of patients (%). We chose MIV as the dependent variable, and the independent variables were LDH, ALC, platelet count, ferritin, and CPR. To analyze the association between the independent variables and MIV, the Pearson χ2 test was used, considering a type I error < 5%. A binomial logistic regression analysis was used for the joint evaluation of variables associated with MIV. The significant variables with P <.05 in the univariate analysis were selected for the regression analysis performed by the stepwise backward method (likelihood ratio). The variables that kept P ≤.05 after adjustments remained in the multiple regression model. A receiver operating characteristic (ROC) analysis was performed to measure the diagnostic/predictive accuracy of each significant variable.

Moreover, we developed a classification tree analysis using the chi-squared automated interaction detection (CHAID) growing method. This nonparametric analysis examines interactions among variables to create a decision tree without assuming that independent and dependent variables are linked by linear relationships. All statistical analyses were carried out using SPSS, version 21.0. Because the sample size was small (n = 160), we could not conduct an internal validation analysis.