Q & A
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June 2007 Q: Patients with livedo vasculitis (clinically livedo reticularis) may have platelet antiphospholipid antibodies, which are treated with anticoagulants. In a patient who clinically has livedo reticularis and is taking Coumadin for chronic atrial fibrillation, can the antiphospholipid antibody test be negative (within normal limits)? A. Not all cases of livedo reticularis have antiphospholipid antibodies. According to the literature, only about one third to one fourth have these antibodies. There is no specific treatment for antiphospholipid antibodies—only preventive anticoagulation when they are associated with thrombotic problems. Anticoagulation with warfarin or the use of aspirin has no effect on the presence of these antibodies or a lupus anticoagulant. Therefore, this patient who is receiving warfarin therapy for atrial fibrillation does not have a false-negative test. However, lupus anticoagulants and antiphospholipid antibodies are very heterogeneous and, unless a variety of tests are used, the diagnosis could be missed.
Bibliography
Sneddon IB. Cerebro-vascular lesions and livedo reticularis. Br J Dermatol. 1965;77:180–185. William E. Luper, MD Q. We perform manual cell counts on cerebrospinal fluids in our hematology laboratory. We recently received a CSF specimen from a newborn containing nucleated RBCs. The formula we use to correct the automated WBC count for NRBCs when we perform a CBC doesn’t apply to manual cell counting in the hemacytometer. What is an appropriate formula to correct the manual CSF WBC count for NRBCs? A. Nucleated red blood cells would never normally be found in cerebrospinal fluid. If they are present when a differential count is performed on a Wright-stained cytocentrifuge preparation, they indicate that the CSF has been contaminated by blood (assuming there are NRBCs in the blood) or by bone marrow (due to inadvertent entry into the vertebral marrow while trying to maneuver the needle through a small space past bones with thin cortexes). Either way, they indicate that the white cell count has been altered by the introduction of blood or marrow and that this needs to be considered by the clinician in evaluating the significance of the white cell count.
Appropriate laboratory practice is to report NRBCs in the nucleated cell differential and include a comment that “NRBCs indicate bone marrow (or blood) contamination, interpret the white count with caution.” There have been a number of publications discussing the potential perils of “correcting the CSF white count” for blood contamination, which indicate that overcorrection of the white cell count is a significant risk. No studies of “correction” for marrow contamination exist, and it is difficult to determine how this might be done. Bibliography Novak RW. Lack of validity of standard corrections for white blood cell counts of blood-contaminated cerebrospinal fluid in infants. Am J Clin Pathol. 1984;82:95–97. Robert W. Novak, MD Chair, CAP Hematology and Clinical
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