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Positive antibody test without detectable specific antibodies;part II:causes and relationships

Methods:Described in part I ; here relationships among features arediscussed.Results:Significant differences (P<0.05) and relationships ofinterest were noted. Sex. In female vs male patients frequent fea-tures were: crossmatch as only reactivity at PT (45.8% vs 28.2%), positive LCT (59.4% vs 26.1%), lymphocytotoxic HLA antibodies(LyTxAb) (13.3% vs 4.9%) and reactivity ‘positive screening, nega- tive panels’ (5.7% vs 2.5%) ; in males non- specific cold antibodies(7.4% vs 1.0%) and antibodies to reagents (4.9% vs 0) were noted.Age. In patients >60 vs <30 reactivity was often found at PT(65.1% vs 35.8%), caused by LyTxAb (21.7% vs 5.4%), anti-Bga(8.4% vs 2.7%) or ‘positive crossmatch, negative panels’ (9.6% vs0), but rarely by laboratory mistake (37.3% vs 59.5%) or later rec-ognized antibody (1 of 6 patients). Subsequent antibody tests: Testswere subsequently positive more often if reactivity was found at PT(79.3% vs 20.7% at BG), as positive antibody screening (41.7% vs29.2% if positive crossmatch), with positive panels (48.3% vs 12.2%if negative). Subsequent tests were positive in only 43.8% patientswith LyTxAb, 50% with anti-Bga, 1 of 3 with antibodies to reagentand in no case with ‘positive crossmatch, negative panels’. Tech-niques. LCT was positive in 60% and 45.5% tested samples foundat urgent and routine PT (DiaMed), vs 0 at BG. All 18 cases due toLyTxAb, 8 of 9 anti-Bga and 6 of 8 ‘positive antibody screening, negative panels’ were found by DiaMed. At BG (Ortho) 71.4% coldantibodies and 64.6% laboratory mistakes were found. Positive anti-body test: Identification was negative in 78.6% screening-onlycases ; 69% of them were caused by laboratory mistake. LyTxAbwere found in 67.9% crossmatch-only cases ; 77.8% reactivitiescaused by LyTxAb were crossmatch-only. Identification. AHG panelwas positive in 60% cases with LyTxAb (in 2 with papainized panel)and often due to ‘IgG antibodies of unknown specificity’ (29.7%), anti-Bga (24.3%), contaminated sample (16.2%), but also to laterrecognized specific antibody (10.8% cases). Strength of reaction:Laboratory mistake was noted in 61.6% of ‘w’, 41.3% of ‘1+’, 46.4%of ‘2+’ and 58.8% of ‘3+and 4+’ antibody screenings (ns). Diagno-sis. In patients with solid and hematologic malignancy reactivitywas often found at PT (80% and 81.3% of patients, respectively), due to positive crossmatch (40% and 50% ; 0 and 4.3% patients withliver and cardiac diseases) and caused by LyTxAb (16.7% and31.3%) or ‘crossmatch/screening positive, panels negative’ (16.7%patients with solid tumors). In patients with liver and cardiac diseases reactivity was often found at BG (83.3% and 68.0% ofpatients), due to laboratory mistake (50% and 60%) or cold anti-bodies (16.7% and 12%), respectively.Discussion:Features of non-specific reactivity depended on sex, age, positive antibody test, diagnosis and, moreover, used tech-niques, sometimes in very distinctive manner. This analysis mightbe of considerable help in planning of laboratory tests, but also inquick analysis of unexpected results and choice of further testing, particularly in urgent situations.

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