Ralf Karger

Diagnostic performance of the platelet function analyzer (PFA-100) for the detection of disorders of primary haemostasis in patients with a bleeding history-a systematic review and meta-analysis.

The Platelet Function Analyzer (PFA-100®) is increasingly being used in the workup of patients with a bleeding diathesis. A profound knowledge of the possible diagnostic performance of this test is essential in order to make sound clinical decisions based on its results. It was the aim of this study to systematically review the published literature and provide valid estimates of the diagnostic performance of the PFA-100® for detecting disorders of primary haemostasis in newly presenting patients with a bleeding diathesis. A comprehensive literature search was performed for studies published between January 1994 and February 2006. Studies were eligible for the systematic review if they provided data supposed to be applicable to the determination of the diagnostic performance of the PFA-100®. Furthermore, they were included in a meta-analysis if study reporting allowed calculation of sensitivity and specificity and if study quality ensured minimized biases of these estimates for the described clinical setting. Pooled weighted sensitivity, specificity and diagnostic odds ratio were calculated applying random effects modelling and constructing summary operator characteristic curves. This was done separately for the available test modifications using either collagen/epinephrine (PFA-EPI) or collagen/adenosine-diphosphate (PFA-ADP) for platelet activation. Thirty-six articles were included in the systematic review. Six studies met our eligibility criteria for a meta-analysis. The major reason for exclusion from the meta-analysis was a case-control design. A total of 1486 and 1259 patients were included in the meta-analysis of the diagnostic performance of the PFA-EPI and PFA-ADP, respectively. Pooled weighted sensitivity and specificity of the PFA-EPI/PFA-ADP in detecting a disorder of primary haemostasis were: 82.5/66.9% (95%-confidence interval (95%-CI): 76.0–88.9%/57.9–75.9%), and 88.7/85.5% (95%-CI: 84.3–93.1%/82.0–89.1%). 83/75% of patients with a positive PFA-EPI/PFA-ADP result do have a disorder of primary haemostasis whereas 88/79% with a negative PFA-EPI/PFA-ADP result do not. The PFA-EPI appeared to have a higher sensitivity and better predictive values than the PFA-ADP in detecting disorders of primary haemostasis, although a rigorous gold standard definition for a disorder of primary haemostasis, particularly for platelet disorders, was not applied in most studies. The majority of the studies lacked important requirements for quality and reporting, precluding a more precise and definitive characterization of the clinical utility of the PFA-100®. This emphasizes the need for an evidence-based critical appraisal of diagnostic studies in haemostasis research in order to promote the conducting of studies that produce clinically relevant results.

Influence of Different Hydroxyethyl Starch (HES) Formulations on Fibrinogen Measurement in HES-Diluted Plasma

Background: Fibrinogen is the first coagulation factor becoming critical in dilution coagulopathy. Volume replacement in major blood loss is performed with large volumes of crystalloid and colloid solutions. The latter has been shown to compromise accurate photo-optical measurement of fibrinogen. This study determined the influence of different hydroxyethyl starch (HES) formulations. Methods: Citrated plasma samples of 8 healthy volunteers were diluted by 30% or 50% with either HES 10% (200/0.5; HES-200), HES 6% (70/0.5; HES-70), or HES 6% (450/0.7; HES-450). Fibrinogen concentrations were determined by photo-optical measurement (Behring coagulation system [BCS]: derived fibrinogen, or Clauss fibrinogen, calibrated for high [CLS] or low fibrinogen concentrations [CLS-low]) as well as mechanical end point determinations (KC4: CLS-KC4). Measured values were compared with calculated values. Results: On average and across all photo-optical methods, fibrinogen concentrations were overestimated, particularly with HES-200. Hydroxyethyl starch-70 and HES-450 did not differ much from each other. Overestimation was relatively greater for 50% dilutions with all HES formulations. Surprisingly, overestimation was most prominent with CLS-low, the method supposed to most reliably measure low fibrinogen concentrations; overestimation amounted to 92% and 120% with HES-200, 54% and 73% with HES-70, and 51% and 79% with HES-450, for 30% and 50% dilutions, respectively. In contrast, CLS-KC4 always yielded sufficiently accurate results. Conclusions: The study showed that all HES solutions more or less impaired the fibrinogen measurement with the photo-optical method. In particular, overestimation with CLS-low may prevent timely fibrinogen replacement in major blood loss. Hydroxyethyl starch concentration appears to be more relevant for this effect than its molecular size.

Leukodepletion of autologous whole blood has no impact on perioperative infection rate and length of hospital stay

BACKGROUND: Several mechanisms have been proposed as possible causes of transfusion‐related immunomodulation (TRIM) after allogeneic transfusion. If one of these mechanisms, the release of mediators of immunity and inflammation (“biologic response modifiers”[BRMs]) from disintegrating blood cells during storage of blood products, really causes TRIM, it should in principle also occur after autologous transfusion. As a consequence, prestorage leukoreduction of autologous blood should be able to prevent the clinical consequences of TRIM after autologous transfusion.

Photo-Optical Methods Can Lead to Clinically Relevant Overestimation of Fibrinogen Concentration in Plasma Diluted With Hydroxyethyl Starch

Background: Adequate fibrinogen concentration is a crucial component of sufficient perioperative/posttraumatic hemostasis. In major blood loss, large volumes of fluids are being administered, which have been shown to interfere with valid determination of fibrinogen concentration. This may lead to wrong treatment decisions. We studied the variables that cause the discrepancies between measured and true fibrinogen concentrations in samples diluted with volume replacement fluids. Methods: Citrated plasma samples of healthy volunteers were diluted by 30% and 50% with phosphate buffered saline (PBS), hydroxyethyl starch (HES) 10% (200/0.5), or gelatine (GEL). Fibrinogen concentrations of diluted samples were derived from the prothrombin time (PT) and the Clauss method (CLS) was applied. With the latter, several modifications and combinations of detection principles and thrombin reagents were investigated. Values were compared with ‘‘true,’’ that is, calculated values based on the results of undiluted samples for each method. Results: Photo-optical methods resulted in significant overestimation of the fibrinogen concentration in blood diluted with HES, depending on the thrombin reagent used. This was particularly true for modifications of the CLS aimed at measuring low fibrinogen concentrations. Use of another thrombin reagent gave satisfactory results for this modification. The validity of mechanical end point determination methods was considered sufficient and was not influenced by the use of different thrombin reagents. Conclusions: Fibrinogen determination methods used in situations of major blood loss need to be validated with samples containing significant amounts of volume replacement fluids, particularly colloids. Only some combinations of test principle, detection method, and reagents will give valid results.

Deformability of Red Blood Cells and Correlation with ATP Content during Storage as Leukocyte-Depleted Whole Blood.

Background: Storage duration of red cells has been associated with increased morbidity and mortality following transfusion. This association has been attributed to the loss of deformability of stored red cells leading to deterioration of microvascular perfusion. ATP content is considered a critical determinant of the deformability of stored red cells. Methods: ATP content and deformability were determined after storage for up to 49 days in 40 leukocyte-depleted whole blood units. Red cell deformability was determined using a laser-assisted optical rotational cell analyzer (LORCA®) employing shear stress (SS) ranging from 0.3 to 30 Pa. Deformability was expressed as the elongation index (EI). EI was correlated with ATP content. Results: ATP content decreased from 3.5 to 1.7 mmol/g hemoglobin. EI increased from 0.03 to 0.05 at an SS of 0.3 Pa, and decreased from 0.62 to 0.59 at an SS of 30 Pa. Correlation coefficient (r) of ATP vs. EI at 0.3 Pa ranged from –0.17 to +0.15 during storage. At 30 Pa, r ranged from –0.03 to +0.45. Correlation increased with storage irrespective of SS, and increased with SS irrespective of storage. Conclusions: ATP content is not a valid surrogate marker for red cell deformability and may not reflect in vivo survival of stored red cells.

The Platelet Function Analyzer (PFA-100) as a Screening Tool in Neurosurgery.

We investigated whether the inclusion of the PFA-100 in the preoperative screening of neurosurgical patients might reduce perioperative bleeding complications. Patients with intracranial space-occupying lesions who were scheduled for neurosurgery underwent routine preoperative PFA-100 testing. In case of an abnormal PFA test, patients received prophylactic treatment with desmopressin. 93 consecutive patients were compared to 102 consecutive patients with comparable characteristics operated before introduction of the PFA-100 testing. 2 patients (2.2%) in the PFA group and 2 patients (2.0%) in the non-PFA group experienced clinically relevant intracranial bleeding confirmed by computed tomography (OR 1.05, 95% CI 0.39–2.82; P = 1.0). Transfusions were not significantly different between the two groups. 13 (14.0%) patients in the PFA group and 5 (4.9%) patients in the non-PFA group received desmopressin (OR 3.2, 95% CI 1.1–9.2; P = 0.045). Preoperative screening with the PFA-100 did result in a significant increase in the administration of desmopressin, which could not reduce perioperative bleeding complications or transfusions.

Extracorporeal blood volume of donors during automated intermittent-flow plasmapheresis and its relevance to the prevention of circulatory reactions

BACKGROUND: Intermittent‐flow plasmapheresis often involves a large extracorporeal blood volume of the donor during the procedure with the concomitant risk of circulatory reactions. Guidelines governing donor recruitment often apply an arbitrary threshold of 15 percent of the donors’ blood volume not to be exceeded during hemapheresis procedures. No data demonstrating the suitability of this approach exist.

Diagnosis and therapeutic management in a patient with type 2B-like acquired von Willebrand syndrome.

Acquired von Willebrand syndrome (AVWS) usually mimics von Willebrand disease (VWD) type 1 or 2A. However, in rare cases, the characteristics of other VWD types can predominate in AVWS that might require careful consideration of differential treatment options. The diagnosis and the treatment of a case of type 2B-like AVWS are discussed. Diagnosis of AVWS was ascertained by determining ristocetin cofactor activity, ristocetin-induced platelet aggregation, von Willebrand factor antigen, collagen binding and characterization of von Willebrand factor (VWF) multimers. Inhibitor presence was sought through mixing experiments, the Bethesda method, and calculation of the in-vivo recovery and plasma half-life of VWF after administration of factor VIII/VWF concentrate. Mutations in the A1 domain of VWF were ruled out by sequencing of exon 28 of the VWF gene. A 34-year-old male patient, putatively diagnosed with type 2B VWD, and undergoing laparoscopic cholecystectomy, did not respond adequately to perioperative hemostatic treatment with desmopressin and high doses of factor VIII/VWF concentrate, requiring the administration of recombinant activated factor VII. Further diagnostic workup revealed AVWS mimicking type 2B VWD, most likely owing to an autoantibody developed in the course of underlying monoclonal gammopathy of undetermined significance. The presence of AVWS should be considered before a diagnosis of type 2B VWD is made, especially in patients with a history atypical for inherited disease.

Blood volume regulation in donors undergoing intermittent‐flow plasmapheresis involving a high extracorporeal blood volume

BACKGROUND: Intermittent‐flow plasmapheresis (IFP) often involves a large extracorporeal blood volume (ECV) of donors during donation. Depending on equipment and donor characteristics, ECV can exceed 20 percent of a donor’s blood volume (BV). It was the aim of this study to delineate mechanisms of BV regulation associated with these volume shifts.

In-line filtration of autologous whole blood.

BACKGROUND:  Experimental data suggest that autologous white blood cells (WBCs) might exert an immunomodulatory effect. Leukodepletion of autologous blood is considered to prevent this unwanted side effect of autologous transfusion. In some cases, however, prolonged filtration or filtration failures occur. Because such autologous units cannot simply be discarded, the interest was in the storage variables of autologous whole blood (AWB) units after prolonged filtration.