printed by Prevalence of Heparin in Samples Submitted for Lupus Anticoagulant Testing Nikhil A. Sangle MD FRCPath 1,3, George M. Rodgers MD PhD 1,2,3, and Kristi J. Smock MD 1,3 Departments of Pathology 1 and Medicine 2, University of Utah Health Sciences Center, Salt Lake City, UT 84132, and ARUP Laboratories 3, Salt Lake City, UT CONTEXT DESIGN RESULTS RESULTS (contd.) Numerous variables can affect assays used for lupus anticoagulant (LA) detection. These include plasma preparation, the content and type of phospholipids, cut-off values, style of reporting, and presence of anticoagulant medications. Amongst these, the presence of anticoagulant medications, such as high concentrations of heparin, is a specific concern due to the possibility of false-positive LA results. The International Society on Thrombosis and Haemostasis (ISTH) subcommittee on Lupus Anticoagulant/Phospholipid dependent antibodies advises caution when performing and interpreting LA testing on patients who are anticoagulated (patients on heparin, warfarin or direct thrombin inhibitors). We searched our reference laboratory database to determine the prevalence of heparin in samples submitted for LA testing. ISTH Criteria for LA IdentificationPositive Results In - 1. Prolongation of a phospholipid- dependent clotting time (screening test) LA, heparin, factor deficiency or factor inhibitor 2. Mixing studies with evidence of an inhibitor LA, heparin, factor inhibitor 3. Evidence of phospholipid- dependence (confirmatory test) LA, potential false-positives with heparin & factor inhibitors  We reviewed 18,676 LA Reflexive Panels performed at ARUP laboratories between June 2009 and December 2009  All samples with prolonged PTT values were tested for the presence of heparin (refer to testing algorithm)  Heparin neutralization was performed on samples containing heparin  Data was analyzed for: # LA positives / LA negatives # containing heparin (prolonged thrombin time & normal reptilase time) # containing a significant amount of heparin (thrombin time >150 seconds & normal reptilase time) # of LA positives containing heparin 1909 samples (10%) were LA positive samples (11%) contained some heparin, and 322 (16%) of these were LA positive. 616 samples (3% of all samples and 31% of samples containing heparin) contained significant heparin (thrombin time >150 seconds). 80 samples (13%) containing significant heparin were LA positive, which represented 4% of samples containing any heparin and 0.4% of all samples. CONCLUSIONS False-positive LA results can occur in samples containing heparin in excess of the reagent neutralization capacity (this can be difficult to determine using the thrombin time). False positive LA test results are of particular concern because patients may receive unnecessary long-term anticoagulant therapy. LA testing guidelines indicate that samples should be obtained prior to, or in the absence of, anticoagulant therapy. Despite these recommendations, our data show that a significant number of samples submitted for LA testing contain heparin. Fortunately, in our study, the number of LA positive samples with a potentially significant heparin concentration were few (0.4% of all samples). LA testing algorithms should employ steps to identify and neutralize heparin and laboratories should provide education regarding appropriate samples for LA testing. DESIGN (contd.) PRIMARY REFERENCES V. Pengo, A. Tripodi, G. Reber, et al. Update of the guidelines for lupus anticoagulant detection. J Thromb Haemost 2009; 7: Brandt JT, Triplett DA, Alving B, Scharrer I. Criteria for the diagnosis of lupus anticoagulants: an update. On behalf of the Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibody of the Scientific and Standardisation Committee of the ISTH. Thromb Haemost 1995; 74: D. 31% of heparin-containing samples contained a significant amount of heparin E. 13% of cases containing significant heparin were LA positive F. 17% of LA positive cases contained some heparin and 4% of LA positive cases contained a significant amount of heparin A. 18,676 cases were included in the study B. 11% of samples contained heparin C. 16% of cases containing heparin were LA positive PTTNot prolongedNo further testing Prolonged Thrombin time Test for heparin Prolonged Not prolonged No heparin present: Proceed with mixing studies and LA confirmatory tests, as indicated Reptilase timeNot prolonged Heparin pattern: Hepzyme the sample and repeat the PTT PTT not prolonged No further testing: PTT prolongation was due to heparin PTT prolonged Prolonged Not a definitive heparin pattern Some samples may be hepzymed, depending on thrombin time Proceed with mixing studies and LA confirmatory tests, as indicated Therapeutic concentration of heparin has been neutralized Proceed with mixing studies and LA confirmatory tests, as indicated False-positive LA results possible if heparin exceeds hepzyme neutralization capacity Heparin identification: PTT result (before & after hepzyme), prolonged thrombin time, normal reptilase time