Introduction and Purpose: Bullous pemphigoid (BP) is the most common autoimmune bullous diseasecharacterized by autoantibodies against the hemidesmosomal proteins BP180 and BP230. Beyond theirantimicrobial affects, tetracyclines have been using in BP for their anti-inflammatory properties (1).However, their effective role on the blood cell markers remains uncertain. In this study we aim todetermine the effects of tetracyclines on hematological parameters including peripheral blood cellcounts, red cell distribution width (RDW); neutrophil to lymphocyte ratio (NLR), monocyte tolymphocyte ratio (MLR); platelet to lymphocyte ratio (PLR); eosinophil to lymphocyte ratio (ELR),mean platelet volume (MPV); C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR),which are the indicators of inflammatory diseases.Materials and Methods: Thirty patients diagnosed with BP who were on remission under doxycycline(n=20) or tetracycline (n=10) along with superpotent topical corticosteroid therapy, were enrolled in thiscross-sectional study. The hematological parameters of the patients before starting tetracycline antibiotictreatment and in the third month of treatment were evaluated retrospectively.Results: 66.7% (n=20) of the patients were female and 33.3% (n=10) were male with the mean age of71.5±14.4 years. The clinical and demographical characteristics of the patients with BP are presented inTable 1. When hematological parameters were compared in the whole study group, there weresignificant decrease in monocyte counts, MLR and CRP level from the baseline to the third month ofthe treatment (p:0.03; p:0.02; p:0.006; respectively) (Table 2). When the treatment subgroups werecompared; doxycycline users (median:14.65) had more lower levels of RDW than the tetracycline users(median:16.40) (p:0.01), while the both groups had comparable levels of peripheral blood cell counts,NLR, MLR, PLR, ELR, MPV, CRP and ESH in the third month of the treatment. At the end of thetreatment period, the eosinophil level was significantly lower in the remission group (median:0.3) thanin the relapsed group (median:1.0) (p:0.033). There was no significant difference in the other peripheralblood cell counts between the remission and the relapsed group. ELR was significantly lower in theremission group both in the baseline (median:0.03) and third month of the treatment (median: 0.14) thanthe relapsed group (medianbaseline: 0.46, median3.month: 0.55) (p:0.016, p: 0.003, respectively).Discussion: A large randomized multicenter study reported doxycycline as a safer alternative tosystemic corticosteroids in patients not suitable for long-term systemic steroid use (1). In our study,RDW level was significantly lower in doxycycline users while, both doxycycline and tetracycline hadsimilar effects on the other hematological parameters. Peripheral monocyte counts, MLR and CRP,which did not differ between the remission and relapsed group, were significantly lower at the end ofthe treatment period. Notably, peripheral eosinophil count which was found to be correlated with BPdisease activity score in a study; was significantly higher in relapsed group (2).Conclusion: Except for RDW, both doxycycline and tetracycline had comparable effects on thehematological parameters. Peripheral eosinophil count and ELR may be a marker for evaluation of responseto tetracyclines in BP patients.