Study of ß1-transferrin and ß2-transferrin using microprobe-capture in-emitter elution and high-resolution mass spectrometry.

Cerebrospinal fluid (CSF) leak can be diagnosed in clinical laboratories by detecting a diagnostic marker ß2-transferrin (ß2-Tf) in secretion samples. ß2-Tf and the typical transferrin (Tf) proteoform in serum, ß1-transferrin (ß1-Tf), are Tf glycoforms. An innovative affinity capture technique for sample preparation, called microprobe-capture in-emitter elution (MPIE), was incorporated with high-resolution mass spectrometry (HR-MS) to study the Tf glycoforms and the primary structures of ß1-Tf and ß2-Tf. To implement MPIE, an analyte is first captured on the surface of a microprobe, and subsequently eluted from the microprobe inside an electrospray emitter. The capture process is monitored in real-time via next-generation biolayer interferometry (BLI). When electrospray is established from the emitter to a mass spectrometer, the analyte is immediately ionized via electrospray ionization (ESI) for HR-MS analysis. Serum, CSF, and secretion samples were analyzed using MPIE-ESI-MS. Based on the MPIE-ESI-MS results, the primary structures of ß1-Tf and ß2-Tf were elucidated. As Tf glycoforms, ß1-Tf and ß2-Tf share the amino acid sequence but contain varying N-glycans: (1) ß1-Tf, the major serum-type Tf, has two G2S2 N-glycans on Asn413 and Asn611; and (2) ß2-Tf, the major brain-type Tf, has an M5 N-glycan on Asn413 and a G0FB N-glycan on Asn611. The resolving power of the innovative MPIE-ESI-MS method was demonstrated in the study of ß2-Tf as well as ß1-Tf. Knowing the N-glycan structures on ß2-Tf allows for the design of more novel test methods for ß2-Tf in the future.

DOAC-Stop in lupus anticoagulant testing: Direct oral anticoagulant interference removed in most samples.

BACKGROUND: The use of direct oral anticoagulants (DOACs) is a convenient therapeutic option for patients at risk of thrombosis. DOACs interfere with clot-based testing for the identification of lupus anticoagulant antibodies (LACs) in patients with antiphospholipid syndrome (APS), a common cause of acquired thrombotic disease. OBJECTIVES: To evaluate a commercially available reagent DOAC-Stop for the removal of DOAC interference encountered in LAC testing. PATIENTS/METHODS: We collected a cohort of 73 test samples from patients on DOAC therapy identified at a large institutional coagulation laboratory from March to December 2019, along with samples from 40 LAC positive and negative control patients not on therapy. Samples were treated with DOAC-Stop and tested for anti-Xa activity and thrombin time for the removal of apixaban, rivaroxaban, argatroban, and dabigatran activity from patient samples. Treated and untreated samples were tested using the activated partial thromboplastin time, silica clotting time, and dilute Russell's viper venom time to evaluate the reliability and utility of DOAC-Stop. RESULTS: DOAC-Stop markedly reduced DOAC interference from test samples (P < .05). DOAC-Stop had no effect on LAC testing in the absence of DOAC therapy, permitting the identification of all LAC positive and negative controls. DOAC-Stop removed false positives and false negatives resulting from DOAC interference and allows the identification of patients meeting criteria for the diagnosis of APS by LAC testing, as well as the detection of patients on rivaroxaban who are triple positive for APS. CONCLUSIONS: DOAC-Stop is an effective adjunct for the clinical laboratory faced with DOAC interference in LAC testing.