Juvenile Idiopathic Arthritis (JIA): The patient's positive ANA screen with a homogeneous and speckled pattern, along with elevated IgG levels, suggests an autoimmune process. JIA is a common condition in pediatric patients that can present with a variety of symptoms, including joint pain and inflammation, and is often associated with positive ANA tests.

Infectious Mononucleosis: Although the patient's monocyte percentage is not significantly elevated, the presence of a positive ANA screen can also be seen in infectious mononucleosis. However, the lack of other specific markers (such as elevated liver enzymes or a positive monospot test) makes this diagnosis less likely.
Chronic Inflammation or Infection: The slightly elevated WBC count and the presence of a positive ANA screen could indicate a chronic inflammatory or infectious process. Further testing and clinical evaluation would be necessary to determine the cause.
Vitamin D Deficiency: The patient's vitamin D level is below the optimal range, which could contribute to various symptoms and may be associated with autoimmune diseases. However, it is not a direct cause of the abnormal bloodwork results.

Systemic Lupus Erythematosus (SLE): Although less common in pediatric patients, SLE is a serious autoimmune disease that can present with a positive ANA test. The homogeneous and speckled patterns, along with the patient's age, make it essential to consider and rule out SLE due to its potential severity.
Lymphoma or Leukemia: Any abnormality in blood cell counts, especially in a pediatric patient, warrants consideration of hematologic malignancies. However, the provided bloodwork does not strongly suggest these conditions at this time.
Chronic Autoimmune Hemolytic Anemia: The slightly elevated RDW and the presence of anemia (Hemoglobin 12.7 g/dL is on the lower end for a male) could suggest a hemolytic process, but other indicators such as elevated indirect bilirubin or lactate dehydrogenase are not provided.

Mixed Connective Tissue Disease: This is a rare autoimmune disorder that can present with features of lupus, scleroderma, and rheumatoid arthritis, and is often associated with a positive ANA test. It is less common in pediatric patients but should be considered in the differential diagnosis of a patient with a positive ANA and suggestive clinical features.
Sjögren's Syndrome: Another rare autoimmune disorder that could present with a positive ANA test, although it is more commonly associated with symptoms of dry eyes and mouth, which are not mentioned in the provided information.