How to interpret and pursue an abnormal complete blood cell count in adults

Abstract

A complete blood cell count (CBC) is one of the most common laboratory tests in medicine. For example, at our institution alone, approximately 1800 CBCs are ordered every day, and 10% to 20% of results are reported as abnormal. Therefore, it is in every clinician's interest to have some understanding of the specific test basics as well as a structured action plan when confronted with abnormal CBC results. In this article, we provide practical diagnostic algorithms that address frequently encountered conditions associated with CBC abnormalities including anemia, thrombocytopenia, leukopenia, polycythemia, thrombocytosis, and leukocytosis. The objective is to help the nonhematologist recognize when a subspecialty consultation is reasonable and when it may be circumvented, thus allowing a cost-effective and intellectually rewarding practice.

FIGURE 1

Diagnostic algorithm for microcytic anemia.

FIGURE 2

Diagnostic algorithm for normocytic anemia. AIHA = autoimmune hemolytic anemia; DIC = disseminated intravascular coagulation; HS = hereditary spherocytosis; PBS = peripheral blood smear; TTP/HUS = thrombotic thrombocytopenic purpura/ hemolytic uremic syndrome.

FIGURE 3

Diagnostic algorithm for macrocytic anemia. MCV = mean corpuscular volume; MDS = myelodysplastic syndrome; MMA = methylmalonic acid.

FIGURE 4

Diagnostic approach to thrombocytopenia. ANA = antinuclear antibody; DIC = disseminated intravascular coagulation; HIT = heparin-induced thrombocytopenia; HIV = human immunodeficiency virus; ITP = idiopathic thrombocytopenic purpura; LDH = lactate dehydrogenase; PBS = peripheral blood smear; SPEP = serum protein electrophoresis; TTP/HUS = thrombotic thrombocytopenic purpura/hemolytic uremic syndrome.

FIGURE 5

Diagnostic algorithm for polycythemia vera (PV). *Clinical clues for PV include splenomegaly, thrombosis, aquagenic pruritus, and erythromelalgia. Laboratory clues for PV include thrombocytosis, leukocytosis, and increased leukocyte alkaline phosphatase score. Janus kinase 2 (JAK2) screening is to detect the V617F mutation that occurs in most patients with PV. BM = bone marrow; CBC = complete blood cell count; MPD = myeloproliferative disorders. †Alternatively, one can consider mutation screening for JAK2^V617F to help decide necessity of BM examination.

FIGURE 6

Diagnostic approach to thrombocytosis. *Clinical evidence of reactive thrombocytosis (RT) includes the presence of infection, inflammatory condition, trauma or surgery, malignancy, hemolytic anemia, iron deficiency anemia, recent bleeding, and history of splenectomy. BM = bone marrow; CBC = complete blood cell count; CRP = C-reactive protein; FISH = fluorescence in situ hybridization; JAK2 = Janus kinase 2; PBS = peripheral blood smear. See text for interpretation of results of testing for serum ferritin and CRP levels and PBS.