BackgroundSome important hematological indices implement acute phase reactions. They can be used to assess disease activity and therapeutic response in many inflammatory conditions. This work aimed to determine whether different hematological indices can be used to assess disease activity and therapeutic response in patients with ankylosing spondylitis (AS) on biological drugs.Patients and methodsNinety-seven AS patients and a similar number of controls were involved in the current study. The Ankylosing Spondylitis Disease Activity Score (ASDAS) was used to assess the disease activity. Different complete blood count parameters and indices were assessed.ResultsThere was a significant difference between the patients and controls as regards mean corpuscular volume, mean corpuscular hemoglobin, red blood cells count, red cell distribution width, mean platelet volume, platelet-to-lymphocyte ratio (PLR), and systemic immune-inflammation index (SII). Moreover, there was a statistical correlation between ASDAS on one side and hemoglobin (Hb), hematocrit (HTC), lymphocyte count, neutrophil-to-lymphocyte ratio (NLR), PLR, and SII on the other side. When the patient group was divided into 2 subgroups according to ASDAS, with patients with inactive and low disease activity in one subgroup and those with very high and high disease activity in another subgroup, there was a significant difference as regards Hb, HTC, mean corpuscular hemoglobin concentration, NLR, PLR, SII, and also ESR and CRP levels. Moreover, there was a significant correlation between PLR and SII levels on one side and ESR on the other side.ConclusionHematological indices such as PLR, NLR, and SII might be potential markers for follow-up of disease activity and therapeutic response in AS patients treated with biological therapy. This emphasizes the significance of a comprehensive approach for AS patient assessment and follow-up of therapeutic drugs, considering inflammatory markers, hematological indices, and disease activity scores.