TABLE 1.
Studies and main findings for lymphocyte count in Covid‐19 patients
| First author (year) | Region | Study period | Sample size | Categorization of hematological factors | Main findings |
|---|---|---|---|---|---|
| Guan (2020) 16 | 552 hospitals in 30 provinces, autonomous regions, and municipalities in mainland China | 11 December 2019 – 31 January 2020 | 1099 | Lymphocytopenia: lymphocyte count of less than 1500 cells/mm3 | Lymphocytopenia was present in 83.2% of patients on admission. 92.6% (50/54) of patients with the composite primary endpoint (admission to an intensive care unit, use of mechanical ventilation, or death) presented with lymphocytopenia vs 82.5% (681/825) of patients without the primary endpoint (P = .056 a ). Severe cases presented lymphocytopenia more frequently (96.1%, 147/153) vs non‐severe cases (80.4%, 584/726); P < .001 a |
| Huang (2020) 17 | Jinyintan Hospital, Wuhan, China | 16 December 2019, to 2 January 2020 | 41 | Low lymphocyte count of <1.0 x109 lymphocytes per Liter | 85% (11/13) of patients needing ICU care presented low lymphocyte count vs 54% (15/28) of patients that did not need ICU care (P = .045). |
| Wang (2020) 19 | Zhongnan Hospital, Wuhan, China | 1 January to 3 February 2020 | 138 | Lymphocytes treated as a continuous variable, x109 per Liter | ICU cases presented with lower lymphocyte count (median:0.8, IQR: 0.5‐0.9) versis non‐ICU cases (median: 0.9, IQR: 0.6‐1.2); P = .03. Longitudinal decrease was noted in non‐survivors. |
| Wu (2020) 20 | Jinyintan Hospital, Wuhan, China | 25 December 2019, to 13 February 2020 | 201 | Lymphocytes treated as a continuous variable, x109 /mL in a bivariate Cox regression model | Lower lymphocyte count was associated with ARDS development (HR = 0.37, 95%CI: 0.21‐0.63, P < .001 in the incremental model); the association with survival did not reach significance (HR = 0.51, 95%CI: 0.22‐1.17, P = .11) |
| Young (2020) 21 | Four hospitals in Singapore | 23 January to 3 February 2020 | 18 | Lymphocytes treated as a continuous variable, x109 per L; lymphopenia was defined as <1.1 × 109/L. | Lymphopenia was present in 7 of 16 patients (39%). Median lymphocyte count was 1.1 (IQR: 0.8‐1.7) in patients that required supplemental O2 and 1.2 (IQR:0.8‐1.6) in those that did not; no statistical comparison was undertaken. |
| Fan (2020) 22 | National Centre for Infectious Diseases, Singapore | 23 January to 28 February 2020 | 69 | Lymphopenia: lymphocyte count of <0.5 × 109/L. | Lymphopenia at admission (4/9 of ICU patients vs 1/58 non‐ICU patients, P < .001) and nadir lymphopenia during hospital stay (7/9 of ICU patients vs 1/58 non‐ICU patients, P < .001) were associated with need for ICU. |
| Yang (2020) 27 | Jinyintan Hospital, Wuhan, China | 24 December 2019, to 9 February 2020 | 52 critically ill patients | Lymphocytes treated as a continuous variable (×109/L); lymphocytopenia presented but not defined | Lymphocytopenia occurred in 44 (85%) of critically ill patients, with no significant difference between survivors and non‐survivors. A numeric difference in lymphocyte count was noted in non‐survivors vs survivors (0.62 vs 0.74). |
| Zhou (2020) 31 | Jinyintan Hospital and Wuhan Pulmonary Hospital, Wuhan, China | 25 December 2019, to 31 January 2020 | 191 | Lymphocyte counts treated as a continuous variable (×109/L) in a multivariate logistic regression model | Lower lymphocyte count was associated with higher odds of death at the univariate analysis (OR = 0.02, 95%CI: 0.01‐0.08; P < .001); at the multivariate analysis, the finding lost significance (OR = 0.19, 95%CI: 0.02‐1.62; P = .13) |
| Arentz (2020) 28 | Evergreen Hospital, Washington State, USA | 20 February 2020, to 5 March 2020 | 21 ICU patients | Low lymphocyte count (less than 1000 cells/μL) | Low lymphocyte count was noted in 14/21 (67%) of critically ill patients. |
| Bhatraju (2020) 29 | Seattle region, Washington State, USA | 24 February 2020, to 9 March 2020 | 24 ICU patients | Lymphocyte counts presented as a continuous variable; definition of lymphocytopenia was not provided | Lymphocytopenia was common (75% of patients), with a median lymphocyte count of 720 per mm3 (IQR: 520 to 1375). |
| Deng (2020) 30 | Wuhan, China | Tongji Hospital and Hankou branch of Central Hospital of Wuhan, China | 1 January 2020 to 21 February 2020 | Lymphocyte counts treated as a continuous variable (×109/L) | On admission, patients in the death group exhibited significantly lower lymphocyte count (median: 0.63, IQR: 0.40‐0.79) × 109/L vs 1.00, IQR: 0.72‐1.27 × 109/L, pP < .001). Patients in the death group also exhibited lower lymphocyte/WBC ratio (median: 7.10, IQR: 4.45, 12.73% vs 23.5, IQR: 15.27‐31.25%, P < .001). The lymphocyte/WBC ratio continued to decrease during hospitalization. |
| Tan (2020) 32 | General Hospital of Central Theater Command, Wuhan, China | Not reported | 90 patients at the validation cohort | Lymphocytes at two time points: day 10‐12 from symptom onset (>20% or < 20%) and day 17‐19 (>20%, 5‐20% and < 5%). | Lymphocytes <20% on day 10–12 signal a pre‐severe disease and lymphocytes <5% on day 17‐19 denote a critical illness. |
Abbreviations: ARDS, acute respiratory distress syndrome; IQR, interquartile range.
a
P‐values calculated by Terpos et al., on the basis of contingency tables (Pearson's chi‐square test) in articles that did not present formal statistical comparisons.