Lymphopenia refers to a decreased number of lymphocytes (a type of white blood cell) in the blood. Generally, this condition can occur because of excessive destruction of lymphocytes or because not enough lymphocytes are being made in the bone marrow and/or the thymus gland. Macrocytosis refers to red blood cells that are larger in diameter than normal red blood cells. Abnormalities in red blood cell production in the bone marrow can cause macrocytosis, and may be related to decreased levels of Vitamin B12 (either due to vitamin deficiency, or due to a condition known as pernicious anemia, which usually causes a decrease in hematocrit as well).

Unfortunately, a number of different conditions can cause the findings that you describe, including medications & drugs (including alcohol), viral infections (including HIV), vitamin deficiencies, and abnormalities of the bone marrow (where blood cells are manufactured) or/and the thymus gland. Excessive thyroid hormone (hyperthyroidism) is sometimes associated with lymphopenia, as well.

Having mentioned these more common causes, however, both lymphopenia and macrocytosis have been observed in patients with Down syndrome, and the lymphopenia may explain why patients with trisomy 21 are at increased risk of developing infections. Of all the potential causes of lymphopenia and macrocytosis, the fact that your son has trisomy 21 makes this the most likely explanation for these abnormal findings in his blood. However, it is not possible to make specific diagnoses or treatment recommendations over the Internet, as you know. Therefore, I can only provide you with possible explanations for the abnormalities in his blood count that you have described.

You might consider having him evaluated by a pediatric hematologist if you remain concerned about these abnormalities. With some fairly simple tests, a hematologist should be able to give you a definitive explanation for these blood abnormalities, although my suspicion is that these findings are most likely associated with his Down syndrome.

I hope that this reponse has been helpful to you, and I wish you and your son happiness and good health.

Sincerely,


Robert A. Wascher, MD, FACS