Ferritin and lymphopaenia as markers of COVID-19 in a haemodialysis population

Background: The COVID-19 PCR swab test has low sensitivity and some infected people are asymptomatic, which makes it possible for inadvertent spread of the virus to occur We reviewed laboratory data in haemodialysis (HD) patients to investigate the utility of routine blood tests as surrogate markers of COVID-19 infection Methods: Retrospective cohort study of data in prevalent patients on HD from 1st March 2020 Blood test results from June 2018 to May 2020 were analysed Results: There were 708 patients 473 were on HD since June 2018 150 had ≥1 PCR test for COVID-19: 69 were positive 268 (37 9%) were female and 282 (39 8%) were of non-white race Median age was 69 years (IQR 56-78) Lymphocytes Mean lymphocyte count at baseline was 1 5 (SD 4 3) Prior to March 2020, the mean monthly prevalence of lymphopaenia was stable at 32 %, but rose to 67 % in COVID +ve patients and 36 % in COVID -ve patients (p;1000μg/L In April, 68 % of COVID +ve individuals had a ferritin of >;1000μg/L compared to 18 % of COVID -ve patients (p<0 001) No significant differences were noted in platelet count, neutrophils and CRP over the study period Conclusions: Our data show a high prevalence of lymphopaenia which was more pronounced in COVID +ve patients There was no similar rise over the previous 2 winter periods, so we feel this was a COVID specific, rather than just a viral phenomenon A low lymphocyte count has recently been associated with adverse prognosis in our patients with COVID-19 Our data support reports which suggest that ferritin could aid screening for COVID-19 in HD patients The degree of elevation of ferritin during the 'COVID months' in our COVID +ve group suggests that the disease was contributing to this This may be due to a cytokine storm and multi-organ involvement and ferritin may prove to be a prognostic factor for COVID-19