Annalisa Fattorini

Thrombotic microangiopathy in pregnancy

Following the initial reports by Moschowitz in 1925 [1] and by Baehr et al. in 1936 [2], Singer [3] and Gasser [4] suggested the terms of “thrombotic thrombocytopenic purpura, TTP” and of “hemolytic uremic syndrome, HUS” to describe related disorders consisting of Coombs’ negative hemolytic anemia, thrombocytopenia, and renal failure. TTP and HUS, commonly referred to as thrombotic microangiopathies (TMA), share features of microangiopathic hemolytic anemia (MAHA), thrombocytopenia, and microvascular thrombotic lesions, and their clinical and pathologic features often overlap. However, TTP and HUS are to be considered different entities, which may both complicate the course of pregnancy and imitate more frequently occurring syndromes, like pre-eclampsia, acute fatty liver, HELLP and SLE in association with antiphospholipid antibodies [5].

Disappearance of anti-PF4/heparin antibodies under prolonged fondaparinux administration in a patient with DVT associated with LMWH-induced thrombocytopenia

Disappearance of anti-PF4/heparin antibodies under prolonged fondaparinux administration in a patient with DVT associated with LMWH-induced thrombocytopenia -

Use of INR calibrator plasmas in the routine coagulation laboratory: A study of two thrombolastin reagents

INR values may be either calculated with the ISI values supplied by thromboplastin manufacturers or are directly extrapolated from certified INR calibrator plasmas. We tested the principle of local INR calibration using INR calibrator plasmas (PT-Multi Calibrator, Siemens), two thromboplastin reagents (Neoplastin Plus, rabbit brain, Stago, coagulometer-specific ISI 1.31, and Innovin, recombinant human tissue factor, Siemens) and the same coagulometer (STA-R, Stago) in 100 patients on warfarin. Using a ISI value of 0.77 with Tomenson correction for Innovin (correction factor=1.09), INR values of patients were similar with the two reagents, with a bias of 0.03 INR units and no significant regression of the difference over the average INR by method comparison analysis. With the INR calibrator plasmas, INR values with Neoplastin Plus were lower than Innovin values with an average bias of 0.39 INR units and a significant regression of the difference over the average INR (r=-0.91). Significant bias (0.16 INR units, p<0.00001) and regression (r=-0.77) was also observed by comparison of Neoplastin Plus INRs with Innovin calibrated INRs. Based on a therapeutic INR interval of 2.0 to 3.5, discordance in warfarin dosing was approximately 3 times higher with INR calibration (27% vs 11%). Because of non commutability with fresh plasma samples, local INR calibration with lyophilized calibrator plasmas may not be valid for some reagent-instrument combinations.

Tempo di protrombina: quale denominatore per il PT Ratio e quali possibilità di utilizzo dell’INR al di fuori della terapia anticoagulante orale

RiassuntoPremesseNella pratica di laboratorio, il tempo di protrombina (PT) viene utilizzato per la diagnostica dei difetti congeniti o acquisiti della coagulazione o per il monitoraggio della terapia con i farmaci anticoagulanti orali. L’espressione del risultato in termini di INR è raccomandata solo nell’ultimo caso, ma in molti laboratori si utilizza lo INR anche per i pazienti non anticoagulati. Inoltre, come denominatore per l’espressione dei risultati del PT viene raccomandato il “mean normal PT” (MNPT), ma questo è spesso sostituito da un plasma “normale” liofilo, con la conseguenza di intervalli di normalità potenzialmente diversi con la stessa combinazione reagente-coagulometro.MetodiL’imprecisione di due tromboplastine del commercio (Neoplastin Plus, cervello di coniglio, Roche, e Innovin®, fattore tissutale umano ricombinante, Siemens) è stata testata sul medesimo coagulometro (STA-R, Roche) con plasmi liofili normali e patologici (Roche, control plasma 1 and 2; Siemens, normal and abnormal plasma and INR calibrator L1). L’intervallo di normalità dei rapporti del PT (PT Ratio) con i due reagenti è stato ottenuto per 40 volontari adulti apparentemente sani utilizzando il MNPT (calcolato in precedenza su 20 altri volontari sani) o i plasmi “normali” liofili come denominatore. Il paragone delle diverse modalità di espressione del PT Ratio con i due reagenti è stato condotto su 200 plasmi da pazienti esterni (n=90) od ospedalizzati (n=110) non anticoagulati. I risultati sono stati anche paragonati utilizzando lo INR.RisultatiL’imprecisione totale (CV%) dei due reagenti, valutata con i plasmi normali e patologici ricostituiti, era simile e variava da 1,1% a 2,5%. Nei controlli, i PT Ratio ottenuti con i due reagenti erano simili e la media non differiva da 1,0 (p ≥0,17) utilizzando il MNPT come denominatore, ma le medie risultavano significativamente diverse da 1,0 con i plasmi normali liofili (da 0,90±0,07 a 1,05±0,08, p ≤0,03). Nei pazienti, i valori di PT Ratio erano simili solo quando si utilizzava il MNPT a denominatore. Utilizzando una procedura WHO semplificata e assumendo Neoplastin Plus (ISI coagulometro-specifico =1,31), come tromboplastina di riferimento, l’indice di sensibilità coagulometro-specifico di Innovin® risultava pari a 0,77 (0,73–0,80, LC al 95%), con correzione di Tomenson (10−d) pari a 1,09. La trasformazione dei PT Ratio in INR dava luogo, indipendentemente dal termine a denominatore, a significative differenze tra le due tromboplastine, e la percentuale dei pazienti con valori anormali di PT con Innovin® saliva da 38,5 a 62,5.ConclusioniI plasmi liofili commerciali “normali” non sono un valido sostituto del MNPT nel determinare gli intervalli di normalità del PT, e dovrebbero essere utilizzati solo per il controllo di qualità. L’espressione dei risultati del PT come INR nei pazienti non anticoagulati dà luogo a falsi valori anormali e andrebbe evitata nella pratica di laboratorio.SummaryBackgroundIn routine laboratory practice, the prothrombin time (PT) is used either to detect acquired or congenital deficiencies of the clotting system or to monitor anticoagulant therapy with vitamin K antagonists. Expression of results as INR is recommended only for the latter case; still in many laboratories INR values are reported irrespectively of whether plasma samples are from patients on oral anticoagulation. In addition, for the denominator term in the expression of PT results, some laboratories use commercial lyophilized normal plasma instead of the mean normal prothrombin time (MNPT), which may result in different normal ranges with the same reagent-coagulometer combination.MethodsOn the same coagulometer (STA-R, Roche), the imprecision of two thromboplastin reagents (Neoplastin Plus, rabbit brain, Roche, coagulometer-specific ISI 1.31, and Innovin®, recombinant human tissue factor, Siemens) was tested with reconstituted lyophilized normal and abnormal plasmas (Roche, control plasma 1 and 2; Siemens, normal and abnormal plasma and INR calibrator L1). The normal range of PT ratios with the two thromboplastin reagents was tested in 40 apparently healthy subjects using either the MNPT, previously determined in a different series of 20 volunteers, or the lyophilized normal plasmas as denominator term. A comparison of the two modalities of PT ratio expression with the two reagents was conducted on 200 plasma samples from out- (n=90) and in-patients (n=110) not on oral anticoagulation. Results in patients were also compared with the INR modality of expression.ResultsTotal imprecision (CV%) of the two reagents, tested with reconstituted normal and abnormal plasmas, was similar and ranged from 1.1% to 2.5%. In controls, average PT ratios were similar with the two thromboplastin reagents when using the MNPT as denominator term and they did not differ significantly from 1.0 (p ≥0.17). With the normal lyophilized plasmas as denominator term, they consistently differed from 1.0 (from 0.90±0.07 to 1.05±0.08, p ≤0.03). In patients, average PT ratios were similar only when using the MNPT as denominator term. According to a simplified WHO procedure and assuming Neoplastin Plus as the reference thromboplastin, the coagulometer-specific SI of Innovin® was 0.77 (95% confidence limits: 0.73–0.80), with Tomenson’s correction (10−d) equal to 1.09. When PT ratios of patients were transformed into INR values, these differed significantly irrespective of the denominator term, and the percentage of patients with abnormal prothrombin time values with Innovin® increased from 38.5 to 62.5.ConclusionsCommercial “normal” plasmas are no substitute for the MNPT in determining normal ranges for the prothrombin time, and should be used only for the purpose of quality control. Expression of PT results as INR in patients not on oral anticoagulation is misleading and should be avoided in routine laboratory practice.