The symptoms and investigation results provided help us diagnose the condition:
- Gum bleeding and fever indicate a possible hematological disorder.
- Low total leukocyte count (TLC) and low platelet count suggest bone marrow suppression or failure.
- General examination being unremarkable rules out significant physical anomalies.
- Low reticulocyte count indicates reduced red blood cell production, pointing towards potential bone marrow issues.
- Absent megakaryocytes indicates a lack of platelet-producing cells in the bone marrow.
- The absence of immature cells suggests a lack of new blood cell production across all lineages.
Based on these findings, the most likely diagnosis is
aplast anemia. This condition is characterized by bone marrow failure leading to decreased production of red blood cells, white blood cells, and platelets, matching all the provided symptoms and investigation results.