Infectious mononucleosis in an outpatient population - Diagnostic utility of 2 automated hematology analyzers and the sensitivity and specificity of Hoagland's criteria in heterophile-positive patients

Objectives,To determine the sensitivity and specificity of 2 modern hematol ogy analyzers in flagging heterophile-positive patients; to determine if he terophile-positive, instrument-flagged specimens contain a larger number or a different spectrum of atypical lymphocytes; to document the overall sens itivity and specificity of Hoagland's morphologic criteria in identifying h eterophile-positive patients in an outpatient population with a clinical di agnosis of mononucleosis; and to examine whether individual morphologic fea tures might aid in the diagnosis of suspected infectious mononucleosis. Design.-A prospective study of patients referred with a clinical diagnosis of infectious mononucleosis who subsequently tested positive for the hetero phile antibody. The control group consisted of a similar population of pati ents who tested negative for the heterophile antibody. Intervention.-Hematology profiles of peripheral blood samples were determin ed with Coulter STKS and Sysmex NE-8000 analyzers. A corresponding Wright-G iemsa-stained blood smear was subsequently examined by a single skilled tec hnologist, who performed a 200-cell white blood cell differential and a 200 -cell lymphocyte differential. A specific morphologic search was made for t he presence of smudge cells or lymphocytes with cloverleaf nuclei. Results.-Using a combination of all flagging criteria, the 2 analyzers iden tified 156 (86.2%) of 181 heterophile-positive patients as meriting further review. The sensitivity and specificity values of the Coulter analyzer in predicting positive heterophile status for the blast flag were 41% and 97.1 %, respectively; for the variant lymphocyte flags, 72.4% and 79.1%, respect ively; and for both flags, 40% and 98.1%, respectively. For the Sysmex anal yzer, the sensitivity and specificity values in predicting positive heterop hile status for the blast flag were 43.4% and 88.6%, respectively; for the variant lymphocyte flag, 15.8% and 90.8%, respectively; and for both flags, 10.5% and 96%, respectively. Considering the classic criteria developed by Hoagland, a lymphocytosis of at least 50% was present in 120 (66.3%) heter ophile-positive patients, while an atypical lymphocytosis of at least 10% o f the total WBC count was noted in 135 patients (74.6%). The sensitivity an d specificity values of a lymphocytosis greater than or equal to 50% for di agnosing heterophile-positive status were 66.3% and 84.5%, respectively, wh ile the sensitivity and specificity of an atypical lymphocytosis greater th an or equal to 10% were 74.6% and 92.3%, respectively. The presence of smud ge cells or cloverleaf lymphocyte nuclei was verified as having high specif icity but low sensitivity for suggesting a diagnosis of infectious mononucl eosis. Conclusion.-Although a number of patients did not meet Hoagland's criteria for the diagnosis of infectious mononucleosis, the flagging systems of mode rn hematology analyzers successfully identified most cases as requiring fur ther review.