Differential Diagnosis for 10-year-old Patient with Anemia and Knee Pain

Single Most Likely Diagnosis

• Iron Deficiency Anemia: The patient's low hemoglobin (11.6 g/dL) and hematocrit (36.1%) levels, along with an elevated RDW (12.7%) and low MCHC (32.1 g/dL), are indicative of iron deficiency anemia. The MCV (93 fL) is near the lower limit of normal, which can also be seen in iron deficiency anemia, especially in the early stages or in cases where it's not severe enough to cause microcytosis.

Other Likely Diagnoses

• Anemia of Chronic Disease: Given the patient's knee pain without trauma, and negative tests for anemia and juvenile arthritis, anemia of chronic disease is a consideration. This condition can present with normocytic anemia (normal MCV), and the patient's MCV is at the lower end of the normal range.
• Thalassemia Trait: Although less likely given the MCV is near normal, thalassemia trait can sometimes present with a near-normal MCV, especially if it's a less severe form like alpha-thalassemia trait. The low MCH (29.8 pg) could be a hint, but further testing (e.g., hemoglobin electrophoresis) would be needed to confirm.

Do Not Miss Diagnoses

• Leukemia: Although the WBC count is normal (4.5 x10^9/L), leukemia can sometimes present with a normal or even low white blood cell count, especially in the early stages. The presence of anemia and unexplained knee pain (which could be due to bone marrow infiltration) makes it crucial not to miss this diagnosis. A bone marrow biopsy or further imaging might be necessary.
• Osteosarcoma or Other Bone Tumors: Unexplained knee pain in a child could be a sign of a bone tumor. Although rare, these conditions are critical to diagnose early for effective treatment.

Rare Diagnoses

• Sickle Cell Disease: Typically presents with hemolytic anemia, and while the MCV is near normal, sickle cell disease can sometimes have a normocytic anemia, especially if there's a recent hemolytic episode. However, the absence of other symptoms (e.g., jaundice) and the lack of mention of specific sickle cell tests (e.g., hemoglobin electrophoresis) makes this less likely.
• Other Hemoglobinopathies: Similar to sickle cell disease, other hemoglobinopathies could present with anemia and might have a near-normal MCV. These would require specific testing to diagnose.