Aim: To highlight the discrepancies in hemogram parameters and blood grouping related to cold agglutinin hemolytic anemia cases which not only helps to the diagnosed underlying pathogen but prevents its complication. Background: Cold agglutinin hemolytic anemia is a rare form of autoimmune hemolytic anemia caused by cold-reacting autoantibodies. The automated hematology analyzer hemogram analysis of these patients sample is related to analytical discrepancies and spurious result. Immunohematology workup including peripheral smear findings, warming the ethylenediamine- tetra-acetic acid (EDTA) sample and cold agglutinin titer helps to resolve such discrepancies and gives a diagnostic clue of rare presentation of atypical pneumonia which responds to specific antibiotics. Case report: A 55-year old male presented with fever, shortness of breath and cough for two weeks. A blood sample drawn for hemogram show high mean cell hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC) and low red blood cells (RBCs) count and hematocrit with discrepancies in blood groupings. Peripheral blood film show significant autoagglutination of RBCs and infective changes in white blood cell morphology suggest cold agglutinin secondary to mycoplasma pneumonia. Further immunohematology workup and serological investigation confirm cold agglutinin autoimmune hemolytic anemia with mycoplasma pneumonia. Conclusion and clinical significance: This case report emphasizes blood count analytical and blood grouping problems related to cold agglutinins and also sensitize to search underlying etiology like mycoplasma pneumonia to start specific antibiotics and to reduce morbidity and mortality.