A (blood) smear campaign

A 40-year-old patient (who insists on being called Pete) is referred to you for evaluation of asymptomatic thrombocytopenia discovered during preoperative blood testing for an elective cholecystectomy. Except for cholelithiasis, he has no significant medical history and no prior surgeries other than uneventful extractions of molar teeth. The referring physician is concerned about the platelet count of 50 000/μL and the fact that “large platelets” were reported from the laboratory. He queries whether a bone marrow examination is indicated for diagnostic purposes, whether corticosteroids should be administered for presumptive idiopathic thrombocytopenic purpura, and whether consideration should be given to changing the operative plan and performing a combined cholecystectomy and splenectomy.

After conducting a history and physical examination, which reveal no additional abnormalities, you examine the patient's peripheral blood smear. You find that almost all of the platelets are very large, some even larger than red blood cells, and many of the granulocytes contain cytoplasmic Döhle body–like inclusions. You unhesitatingly make the diagnosis of May-Hegglin anomaly, a form of inherited thrombocytopenia due to mutations in nonmuscle myosin heavy chain A.1 Then you clear the patient for cholecystectomy, with recommendations to avoid aspirin and to have platelet concentrates and autologous red blood cells available in the unlikely event that they are needed. The surgical procedure is undertaken without complications or the need for transfusions. Subsequent evaluation finds that Pete is not the only member of his family with asymptomatic macrothrombocytopenia: a sister and a son are similarly affected.

This case, although fictional, illustrates the value of examining the peripheral blood smear in patients referred for hematologic consultation. The conventional Wright-Giemsa–stained blood smear is to the hematologist what urine sediments are to the nephrologist or eyegrounds are to the ophthalmologist: windows to the inner workings of the body in health and disease. And it is arguably more pleasing to look at! As Jandl put it in 1987 and it is still true, “more information can be gained from examining the blood smear than from any other single hematologic procedure.”^2(p33)While I know that all experienced clinical hematologists would agree with this sentiment, over the years I have occasionally seen diagnoses missed and therapeutic plans misguided by the failure of physicians responsible for patient care to personally review blood smears, especially when the workup suggests that there is a hematologic problem.

In this country, abnormalities in the peripheral blood smear are frequently discovered by the clinical hematology laboratory, and they are then vetted by a hematopathologist, who transmits this information to the clinician. However, this sequence of events, although appropriate, is no substitute for a careful review of the blood smear by the patient's physician, whose responsibility it is to synthesize information from the entire clinical and laboratory data base. Since routine analysis of blood smears is a learned behavior and correct interpretation is facilitated by experience, we owe it to the younger generation of physicians, especially hematology trainees, to pass on this skill. More pragmatically, proficiency in blood smear analysis is a procedural requirement for certification in Hematology-Oncology by the American Boards of Internal Medicine and Pediatrics.

Given the importance of peripheral blood smears in hematology practice,Blood has begun publishing illustrative blood smears and occasional bone marrows, accompanied by short explanatory text. This new series is called “Blood Work” (see page 2452 in this issue). The goal is to highlight some of the diagnostic clues and raw beauty inherent in blood smears, with an attempt to educate and perhaps even to titillate, but not to be encyclopedic. Digital photomicrographs are drawn from the Image Bank of the American Society of Hematology, whose editorial board members have graciously helped to select images and permit their use. Readers interested in accessing or contributing high-quality images to the Image Bank are referred towww.ashimagebank.org.

So, trainees, temporarily eschew the microarray and microchip for the microscope. Make it a practice to review blood smears, to become proficient in their interpretation, and to record the results in the patient record, for Pete's sake!