Electron microscopy examination of platelet whole mount preparations to quantitate platelet dense granule numbers: Implications for diagnosing suspected platelet function disorders due to dense granule deficiency

INTRODUCTION

Dense granule (DG) deficiency (DGD) is a feature of some platelet function disorders (PFD) with a prevalence similar to von Willebrand disease. Most laboratories assess for DGD using whole mount platelet preparations and electron microscopy (EM). We evaluated our experiences with this test and associations between DGD and bleeding.

METHODS

Dense granule EM records for 2006-2017 were examined for patients and simultaneously tested controls, and for an overlapping PFD study cohort to evaluate findings and their relationship to bleeding.

RESULTS

More patient than control samples had reduced DG counts (6.5% vs 0.3%, P < .01). DG counts showed no relationship to age or mean platelet volume and had acceptable within-subject variability that was higher for DGD than control participants (28% vs 12%). Repeat tests confirmed DGD in all persons with initial DG counts <4.0/platelet, but not in those with less severe reductions (4.0-4.8 DG/platelet) or normal DG counts (≥4.9 DG/platelet). Aggregometry and adenosine triphosphate release tests, respectively, had only ~52% and 70% sensitivity for DGD. Confirmed DGD by EM was associated with higher bleeding scores and a bleeding disorder.

CONCLUSION

Whole mount EM is useful for the evaluation of suspected PFD due to DGD and detects abnormalities associated with bleeding.

Variability in platelet dense granule adenosine triphosphate release findings amongst patients tested multiple times as part of an assessment for a bleeding disorder

INTRODUCTION

Lumi-aggregometry quantification of platelet dense granule adenosine triphosphate (ATP) release is commonly used for diagnosing platelet function disorders. As the test findings show considerable variability for healthy controls, we postulated that patient findings might also be variable and investigated patients who were assessed for dense granule ATP release defects more than once.

METHODS

Analyses were performed on prospectively collected data for first and second tests for subjects tested for dense granule ATP release defects more than once by the Hamilton Regional Laboratory Program (HRLMP) between January 2007 and June 2013 (cohort I). Similar analyses were performed for subjects who were recruited to a platelet disorder study (cohort II) and were assessed for ATP release defects more than once before October 2015.

RESULTS

A total of 150 unique subjects had multiple ATP release tests. Results with individual agonists were variable for many subjects. While normal findings with all tested agonists were often confirmed by the second test (cohort I: 83%; cohort II: 100%), impaired release with multiple agonists was confirmed in only some subjects (cohort I: 34%; cohort II: 54%). Inconsistent findings were common (cohort I: 36%; cohort II: 39%). ISTH bleeding scores showed no relationship to the test findings. The finding of impaired ATP release with 2 or more agonists on both tests was not associated with an increased likelihood of a definite bleeding disorder.

CONCLUSION

The variability in platelet dense granule ATP release findings amongst patients assessed for diagnostic purposes suggests that the test has limited value for diagnosing platelet disorders.

Effect of standardized perioperative dabigatran interruption on the residual anticoagulation effect at the time of surgery or procedure

ESSENTIALS: Anticoagulants need to be stopped preprocedure so there is little or no remaining anticoagulant effect. We assessed the residual anticoagulant effect with standardized interruption for patients on dabigatran. With this protocol, 80-86% of patients had no residual anticoagulant effect at the time of a procedure. A standardized perioperative dabigatran protocol appears to be safe, but requires further study.

BACKGROUND

In patients taking dabigatran who require treatment interruption for a surgery/procedure, a sufficient interruption interval is needed so that there is little or no residual anticoagulant effect at the time of the surgery/procedure.

METHODS

A prospective cohort study of patients receiving dabigatran (110 mg or 150 mg twice daily) who required an elective surgery/procedure and received a standardized dabigatran interruption protocol based on surgery/procedure bleeding risk and renal function was performed. Before the surgery/procedure, a blood sample was taken for measurement of the prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), and dilute thrombin time (dTT). We determined the proportion of all patients and those having a high bleeding risk surgery/procedure with normal coagulation test results at the time of the surgery/procedure. The APTT and dTT were considered to be most likely to reflect a dabigatran anticoagulant effect. Patients were followed up for 30 days postprocedure to assess for bleeding and thromboembolism.

RESULTS

One hundred and eighty-one patients were studied: 118 with low bleeding risk, and 63 with high bleeding risk. For all patients, the proportions with normal PT, APTT, TT dTT levels were 92.8%, 79.6%, 33.1%, and 80.7%, respectively. In patients with high bleeding risk, the proportions with normal PT, APTT, TT dTT levels were 93.7%, 85.7%, 57.1%, and 87.3%, respectively. During follow-up, there was one (0.6%) major bleed, there were nine (5.0%) minor bleeds, and there was one (0.6%) transient ischemic attack.

CONCLUSIONS

In patients receiving dabigatran who require an elective surgery/procedure, a standardized interruption protocol yielded 80-86% of patients with no residual anticoagulant effect at the time of surgery/procedure, and with a low incidence of bleeding.

Laboratory testing for bleeding disorders: strategic uses of high and low-yield tests

Laboratory testing is essential for diagnosing bleeding disorders. The tests and panels that laboratories currently use for bleeding disorder evaluation are not standardized, although most offer coagulation screening tests in bleeding disorder panels. Some tests for bleeding disorders, including von Willebrand factor multimer assays and tests for rarer disorders, are not widely available. Accordingly, clinicians and laboratories need tailored strategies for evaluating common and rare bleeding disorders. Coagulation screening tests have high specificity, however, false positives and false negatives do occur among subjects evaluated for bleeding disorders and more specific tests (e.g., factor assays) are required to further assess abnormalities. Tests for defects in primary hemostasis have similar high specificity but much greater sensitivity for common bleeding disorders than coagulation screening tests. Nonetheless, extensive testing fails to establish a diagnosis in a significant number of individuals considered to have significant bleeding problems. Rare bleeding disorder investigations are important to diagnose some conditions, particularly those with delayed-onset bleeding, such as factor XIII deficiency, α2 antiplasmin deficiency, plasminogen activator inhibitor-1 deficiency, and Quebec platelet disorder. These issues need careful consideration when assessing patients for congenital and acquired bleeding problems.

Simultaneous measurement of adenosine triphosphate release and aggregation potentiates human platelet aggregation responses for some subjects, including persons with Quebec platelet disorder

Platelet aggregometry and dense granule adenosine triphosphate (ATP) release assays are helpful to diagnose platelet disorders. Some laboratories simultaneously measure aggregation and ATP release using Chronolume® a commercial reagent containing D-luciferin, firefly luciferase and magnesium. Chronolume® can potentiate sub-maximal aggregation responses, normalising canine platelet disorder findings. We investigated if Chronolume® potentiates human platelet aggregation responses after observing discrepancies suspicious of potentiation. Among patients simultaneously tested by light transmission aggregometry (LTA) on two instruments, 18/43 (42%), including 14/24 (58%) with platelet disorders, showed full secondary aggregation with one or more agonists only in tests with Chronolume®. As subjects with Quebec platelet disorder (QPD) did not show the expected absent secondary aggregation responses to epinephrine in tests with Chronolume®, the reason for the discrepancy was investigated using samples from 10 QPD subjects. Like sub-threshold ADP (0.75 μM), Chronolume® significantly increased QPD LTA responses to epinephrine (p<0.0001) and it increased both initial and secondary aggregation responses, leading to dense granule release. This potentiation was not restricted to QPD and it was mimicked adding 1-2 mM magnesium, but not D-luciferin or firefly luciferase, to LTA assays. Chronolume® potentiated the ADP aggregation responses of QPD subjects with a reduced response. Furthermore, it increased whole blood aggregation responses of healthy control samples to multiple agonists, tested at concentrations used for the diagnosis of platelet disorders (p values <0.05). Laboratories should be aware that measuring ATP release with Chronolume® can potentiate LTA and whole blood aggregation responses, which alters findings for some human platelet disorders, including QPD.

Results of a worldwide survey on the assessment of platelet function by light transmission aggregometry: a report from the platelet physiology subcommittee of the SSC of the ISTH

BACKGROUND

Light transmission aggregometry (LTA) is the most common method used in clinical and research laboratories to assess platelet function. However, the method has never been standardized.

OBJECTIVES

As the first step towards development of methodological guidelines, the Platelet Physiology Subcommittee of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis (ISTH) undertook a large, detailed, global survey of LTA practices.

METHODS

Members of ISTH and of External Quality Assurance in Thrombosis and Haemostasis organizations were invited to complete a 129 item, online questionnaire. Results were analyzed anonymously to participant identities.

RESULTS

The online supplement for this article (http://www.isth.org/Publications/OfficialCommunications/PlateletPhysiology/LightTransmissionAggregometry/tabid/201/Default.aspx) contains the full details of the study findings. 359 (244 clinical, 115 research) laboratories from 48 countries participated in the survey. LTA was widely used to assess inherited or acquired bleeding disorders. Common practices were identified in sample collection, processing and analysis and although some are generally considered acceptable, others are not ideal. The agonist concentrations used for LTA varied, and many laboratories used ADP, collagen, epinephrine and Ristocetin, at more than one concentration, in addition to arachidonic acid. The parameters commonly used to assess LTA responses were maximal amplitude or % aggregation, which was considered particularly important, in addition to the presence of a 'secondary wave', deaggregation, shape change and a measure of the lag phase. However, many laboratories did not have appropriate reference intervals.

CONCLUSIONS

This is the largest and most detailed survey of LTA practices ever undertaken. It shows a very high variability in LTA practices worldwide, and, as a consequence, methodological standardization is necessary. The information gathered in this survey will be helpful in the development of ISTH methodological guidelines for LTA.

Diagnostic utility of light transmission platelet aggregometry: results from a prospective study of individuals referred for bleeding disorder assessments

BACKGROUND

Light transmission aggregometry (LTA) is commonly performed to assess individuals for bleeding disorders.

OBJECTIVES

The goal was to evaluate the incidence and spectrum of platelet function abnormalities in a prospective cohort of individuals referred for bleeding disorder assessments after exclusion of thrombocytopenia and von Willebrand disease.

PATIENTS/METHODS

Subjects were healthy controls and patients from a prospective cohort of individuals referred for bleeding disorder assessments after exclusion of thrombocytopenia and von Willebrand disease. LTA was performed by standardized methods using platelet-rich plasma adjusted to 250x10(9) platelets L(-1). Maximal aggregation data were analyzed to determine the likelihood of detecting a platelet function disorder by LTA, and the sensitivity and specificity of LTA for platelet disorders.

RESULTS

The incidence of false positive LTA among subjects excluded of having bleeding disorders was similar to healthy controls. Abnormal LTA was more common in subjects with bleeding disorders and the likelihood of a bleeding disorder was significantly increased (odds ratio 32) when maximal aggregation was reduced with two or more agonists. Receiver operator curve analyses indicated that LTA had high specificity and moderate sensitivity for detecting inherited defects in platelet function and that the LTA agonists 1.25 microg mL(-1) collagen, 6 microM epinephrine, 1.6 mM arachidonic acid and 1.0 microM thromboxane analogue U44619 detected most inherited disorders with abnormal LTA.

CONCLUSIONS

LTA is valuable for detecting platelet function abnormalities among individuals referred for bleeding problems, particularly when the test indicates abnormal responses to multiple agonists.

GENDER DIFFERENCES IN BLEEDING PROBLEMS AND IMPLICATIONS FOR THE ASSESSMENT OF A BLEEDING DISORDER

Background: The value of gender-specific questions in assessing patients for bleeding problems is not well established, nor is the impact of bleeding on sexual and reproductive health. Methods: We administered the CHAT (clinical history assessment tool) to 256 females and 66 males referred for bleeding problems, and 67 female and 32 male healthy controls. This detailed bleeding history questionnaire included questions about sexual health, blood in semen, and bleeding with circumcision, menses, pregnancies, and childbirth. A diagnosis for each patient was established by independent medical record review. The prevalence of symptoms among patients and controls was compared. Results: 80% of patients had bleeding disorders (205 women, 54 men). Men with bleeding disorders did not have significantly increased intercourse-related bleeding, bleeding affecting their sex life, or gender-specific bleeding. Women with bleeding disorders had significantly increased intercourse-related bleeding and bleeding affecting their sex life. They also had significantly increased risks of prolonged menses, menses interfering with lifestyle, and menses requiring medical or surgical therapy (all p values < 0.001). Women with bleeding disorders were more concerned about pregnancy and delivery because of bleeding (p=0.0001), and 38% had been told by a doctor not to become pregnant. Yet they did not have increased risks for pregnancy loss or bleeding during pregnancy (p values > 0.1) and had similar numbers of offspring as controls (mean 2.0 vs.1.7). Conclusion: Gender has an important impact on the manifestations, diagnosis and management of common bleeding disorders. Detailed questions about gender-specific bleeding are useful in assessing women with possible bleeding disorders, as they are at greater risk for bleeding that negatively impacts their sexual and reproductive health.

Vitamin D receptor expression, 24-hydroxylase activity, and inhibition of growth by 1alpha,25-dihydroxyvitamin D3 in seven human prostatic carcinoma cell lines

Although prostatic cancer is often viewed as an androgen-dependent malignancy, a number of other hormones including 1alpha, 25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] are now recognized to modulate its growth and differentiated phenotype. Seven different continuous human prostatic carcinoma cell lines were examined for the presence of biologically active receptors for 1alpha,25(OH)2D3. All seven lines were found to contain mRNA for the vitamin D receptor using an RNase protection assay. Six of the seven cell lines were found to have high-affinity saturable binding sites for 1alpha,25(OH)2D3. The seventh line was found to contain vitamin D receptors by sucrose gradient analysis. All seven lines were found to express 24-hydroxylase activity by a HPLC assay that measures the conversion of 25-hydroxyvitamin D3 to 24,25-dihydroxyvitamin D3. 24-Hydroxylase activity was up-regulated in all seven cell lines by preincubation with 1alpha,25(OH)2D3. In the presence of fetal bovine serum, the growth of four of the seven cell lines was inhibited. In the majority of cell lines growth inhibition was related not only to the number of receptors per cell, but also in inverse proportion to the 24-hydroxylase activity of each cell line. The ubiquitous presence of vitamin D receptor and 24-hydroxylase activity in human prostatic carcinoma cells suggests new alternatives for the pharmacological treatment of advanced prostatic cancer and implies that chemoprevention strategies could also make use of this endocrine axis.