Diseases of the blood involving infants, children, and adolescents are commonly encountered by primary care providers. Many hematologic problems are straightforward and easy to diagnose and manage without involvement of a subspecialty consultant. However, others may be rare, serious, or even life-threatening; these represent complex diagnostic and management challenges. In such cases, engagement of a pediatric hematology-oncology subspecialist is recommended. The American Board of Pediatrics has certified more than 2000 practitioners in this subspecialty. For good reason, hematology and oncology have been combined as a single subspecialty discipline for several decades. One of the first recognizable conditions treated by children’s blood specialists was acute leukemia. As the principles of combination chemotherapy became clear during the 1960s, the drugs used to treat leukemia were also found to be effective in treating solid tumor malignancies. Hematology-oncology thus became a combined specialty by the 1970s and has remained so from the standpoint of board certification. Nevertheless, the increasing complexity of the field during the past few decades has resulted in some practitioners focusing primarily in one clinical area or the other (oncology versus hematology), especially those working in large metropolitan areas where patient numbers justify this sub-subspecialization. Hematology-oncology specialists tend to be concentrated in academic medical centers where they conduct clinical or laboratory research as well as teach and provide patient care. For years, the standard of care in childhood cancer has included these patients’ enrollment, if possible, in peer-reviewed multicenter research studies. More recent advances have also fostered clinical trial participation becoming accepted practice in children with nonmalignant hematologic conditions, such as sickle cell disease and hemophilia.
CLASSIFICATION OF HEMATOLOGIC DISORDERS
Many diseases during childhood involve a specific organ, such as the heart, lungs, kidneys, or brain. Strictly speaking, the blood is not an organ, but a tissue that circulates throughout the body, and as such, an abnormality can have diverse clinical consequences affecting many organs. The primary organ of the blood is the bone marrow cavity, where the majority of blood cells are produced postnatally. In general, the bone marrow rapidly produces and releases millions of blood cells into the circulation when the need arises. For example, during an acute infection, white blood cell counts can rise within hours by 10-fold or more, and acute anemia is often followed by a marked increase in circulating nucleated red blood cells and reticulocytes. Various hematopoietic growth factors are responsible for mobilizing increased numbers of blood cells, although this process may take several days. Other hematologic organs include the spleen and lymph nodes, which contain diverse antibody-producing cells and lymphocytes. The spleen is also a rich source of macrophages that remove aging blood cells, bacteria, and other soluble and particulate matter from the bloodstream.
Most hematologic disorders encountered by pediatricians are mild, transient, and/or secondary to another acute or chronic illness. They are usually identified because of abnormalities in the blood count rather than by signs ...