Mišo Šabovič

The influence of the haemodialysis procedure on platelets, coagulation and fibrinolysis.

In end-stage renal disease, in particularly when treated with haemodialysis, the function of platelets, coagulation and fibrinolytic systems can be disturbed, thus contributing to either thrombotic or bleeding complications. It is important to know whether the currently used haemodialysis procedure itself (by biocompatible membranes and better anticoagulation with nandroparin) affects platelets, coagulation or fibrinolysis. In 15 patients who had been treated with chronic haemodialysis, we measured and compared platelet aggregation (induced by adenosine diphosphate, collagen and epinephrine), the markers of coagulation and fibrinolysis activation (thrombin-antithrombin complexes, thrombin fragments F1+2, D-dimer), and fibrinolytic parameters, i.e. fibrinogen, plasminogen, tissue plasminogen activator (t-PA) and plasminogen activator inhibitor 1 antigen and activity, before and immediately after the regular haemodialysis sessions. We did not find differences between pre- and post-haemodialysis platelet aggregation induced with all agents. Markers of coagulation and fibrinolysis activation remained unchanged during the process of haemodialysis. However, in post-haemodialysis samples, t-PA activity was significantly increased. Other fibrinolytic parameters remained unchanged. In conclusion, our results showed that the current technique of haemodialysis procedure does not affect platelet aggregation or activate coagulation, and therefore, does not contribute to a thrombotic tendency. However, it does directly affect fibrinolysis through activation of t-PA, which might be clinically relevant since this could increase the bleeding tendency in some haemodialysis patients.

Utility of In vitro closure time test for evaluating platelet-related primary hemostasis in dialysis patients

BACKGROUND The platelet aggregation and skin bleeding time (SBT) tests currently used for assessment of hemostasis impairment in dialysis patients have important disadvantages. The authors explored the utility of a novel in vitro closure time test (PFA-100, platelet function analyzer) in which the process of platelet adhesion and aggregation after vascular injury is simulated in vitro in dialysis patients. METHODS Thirty-four long-term dialysis patients were included in the study with 30 healthy volunteers as the control group. In vitro closure time was compared with results from the platelet aggregation and SBT tests. RESULTS In vitro closure time identified more patients and fewer controls with hemostasis impairment. In the patient group, 60%, 40%, and 20%, and in the control group, 0%, 10% and 3% of persons were found to have hemostasis impairment as determined by in vitro closure time, platelet aggregation, and SBT, respectively. In addition, values for patients and controls were significantly different for in vitro closure time (P < 0.05) but not for platelet aggregation or SBT. Thus, closure time appears to be more sensitive and specific than the other 2 tests. No correlation was found between the 3 tests, either in patients or in controls. However, a high correlation (r = 0.73; P < 0.0001) was found between the 2 types of in vitro closure time test (collagen/epinephrine [CEPI] and collagen/adenosine diphosphate [CADP]) in patients and controls. CONCLUSION These results indicate that in vitro closure time can be a useful test for detecting platelet-related primary hemostasis defects in dialysis patients.

The effect of long term, low-dose tranexamic acid treatment on platelet dysfunction and haemoglobin levels in haemodialysis patients

Some previous studies suggest that activation of the fibrinolytic system may induce platelet dysfunction in haemodialysis patients. Accordingly, inhibition of fibrinolysis may improve platelet dysfunction, and speculatively increase haemoglobin levels. We tested this hypothesis. The study group comprised 22 patients (14 male, 8 female, median age 62), who had been on maintenance haemodialysis for more than one year. Patients were treated for three months with low-dose tranexamic acid (TXA), a potent anti-fibrinolytic agent. The dosages of erythropoietin and the haemodialysis procedure were not changed significantly during the study. We primarily followed platelet function (by in vitro closure time test) and haemoglobin values. Patients were divided into those with substantially prolonged (N = 9) and those with slightly delayed or normal (N = 13) in vitro closure time. Treatment with TXA resulted in a significant improvement of platelet function and increased levels of haemoglobin in the first group, and no changes in either platelet function or haemoglobin values in the second group. TXA in the dosage used was biologically active, since a significant decrease in plasminogen and D-dimer were found in both groups. No significant changes in other fibrinolytic parameters or von Willebrand factor were found. No complications in terms of arterial or venous thrombosis were observed. Our pilot study suggests that long-term, low-dose TXA treatment of haemodialysis patients with substantially prolonged in vitro closure time results in a significant improvement of platelet dysfunction and a significant increase in haemoglobin values. These new, promising results merit further investigation in larger studies.

The study of anaemia-related haemostasis impairment in haemodialysis patients by in vitro closure time test.

It is known that anaemia in haemodialysis patients could contribute to haemostasis impairment. However, the precise relation between the degree of anaemia and the degree of haemostasis impairment is not known, nor the optimal level of hematocrit above which anaemia no longer disturbs haemostasis. Our study addresses these clinically relevant questions by employing in vitro closure time test, a new method in which the process of platelet adhesion and aggregation following vascular injury is simulated in vitro in samples of whole blood. We studied 63 haemodialysis patients, with 30 age-matched, healthy controls. Results show that patients with hematocrit below 0.32 (N=28) had significantly impaired primary haemostasis, in contrast to patients with hematocrit above 0.32 (N=35), as measured by both types of closure time test. A significant negative association was found between hematocrit values and closure time (CEPI cartridges: rho=-0.41, p<0.001; CADP cartridges: rho=-0.47, p<0.001). A multiple logistic regression model for predicting prolonged closure time confirmed this finding. Nonparametric curve fitting enabled estimation of the level of hematocrit at which the values of in vitro closure time in haemodialysis patients do not differ from those in the controls at approximately 0.35. ROC analysis confirmed this to be the optimal threshold for predicting prolonged closure time for both cartridges. By using in vitro closure time test, we confirmed that anaemia correlates with the severity of haemostasis impairment. We estimated the target level of hematocrit above which anaemia no longer affects haemostasis to be about 0.35. These new results (and new assay) appear to have clinical value for treating haemodialysis patients.

Intensity of Long-Term Treatment with Warfarin Is Influenced by Seasonal Variations

In a prospective study, which lasted 1 year and was performed on a large cohort of 800 patients treated at an outpatient anticoagulant clinic, we investigated possible seasonal variations in the intensity of the effect of warfarin treatment. For every season – winter, spring, summer and autumn – the mean prothrombin time reported as an international normalised ratio (INR) and the percentages of INR below 2.0 and above 4.0 were calculated. Significant seasonal variations in mean INR measurements were found, with the lowest values in summer and the highest values in autumn (F = 14.2, p < 0.0001). In addition, a trend toward a higher percentage of INR below 2.0 in summer and above 4.0 in autumn was observed. No significant differences were found between older (>65 years) and younger (<65 years) patients, although there was a trend toward more pronounced variations in younger patients. Consideration of seasonal variations might result in more accurate and safe guidance of warfarin treatment.

An unusual case of cortical blindness associated with aortography--a case report.

Transient cortical blindness is a rare but well-recognized benign complication of angiog raphy that is due to neurotoxicity of the contrast agent. The blindness completely resolves in a few days. This report describes a patient suffering an unusual course of cortical blindness following aortography resulting in permanent, partial blindness. It was found that blindness was the consequence of bilateral occipital embolisms. This case emphasizes that cortical blindness associatted with angiography does not always have a favorable outcome, since it might be, in rare cases, due to isolated occipital embolisms, which initially produce a clinical picture identical to that of the neurotoxic effect of contrast agents.

Fibrinolytic parameters and lipoprotein(a) in young women with myocardial infarction.

Impaired fibrinolysis and elevated lipoprotein(a) (Lp[a]) are possible nonclassic risk factors for myocardial infarction (MI) at young age. The fibrinolytic system in young women with MI has not been evaluated yet and the role of Lp(a) is still controversial. The authors determined fibrinolytic parameters and Lp(a) in premenopausal women (mean age 42 ±3 years, n = 22) 0.5 to 6 (mean 3.5) years after MI, who were all without severe classic risk factors and had an otherwise low risk for MI. Elevated levels of tissue type plasminogen activator (t-PA) (p < 0.05) were measured in comparison to 52 age-matched controls; no difference was found in plas minogen activator inhibitor, plasminogen, fibrinogen, euglobulin clotting time and D-dimers. Significantly more MI patients had Lp(a) levels greater than 300 mg/L compared to controls (36% vs 13.5%, p < 0.05). The combination of elevated Lp(a), mild hyperlipidemia, and nonsevere smoking was found in 62.5% of MI patients who had elevated levels of Lp(a), in 23% of all women with MI, and in none of the controls. Elevated t-PA is probably only a marker of increased risk of MI, whereas elevated Lp(a) probably has a causative role. A combination of elevated Lp(a), hyperlipidemia, and nonsevere smoking seems to be a high-risk profile, rela tively common in young women with MI.

Interleukin-6 and antiphospholipid antibodies in women with contraceptive-related thromboembolic disease

OBJECTIVE: The aim of this study was to explore the possible (joint) contributing role of interleukin-6 (IL-6) and antiphospholipid antibodies to the occurrence of the venous thromboembolism in women using oral contraceptives. METHODS: Interleukin-6 and antiphospholipid antibodies (anti-β2-glycoprotein I antibody–immunoglobulin M [IgM], G [IgG], and A [IgA]; anticardiolipin-IgM and IgG; antiphosphatidylserine-IgM and IgG) were measured in 30 women (median age 41, range 28–49 years) in the stable period (on average 3.5 years) after first venous thromboembolism. Sixteen patients used oral contraceptives during the episode of venous thromboembolism (oral contraceptives group), whereas 14 patients did not (non–oral contraceptives group). Thirty-seven age-matched, healthy women served as controls RESULTS: Compared with controls, the oral contraceptives group had elevated IL-6 (median interquartile range 2.3 [1.1–4.3] versus 1.4 [0–2.0] pg/mL, P < .05). The oral contraceptives group had elevated anti-β2-glycoprotein I antibody–IgM in comparison with both the non–oral contraceptives group (median interquartile range 47.5 [2.0–77.0] versus 29.50 [11.00–45.50] OD450, P < .06) and controls (47.5 [2.0–77.0] versus 17.5 [3.5–30.0] OD450, P < .001). Interleukin-6 level in the non–oral contraceptives group was related to obesity, whereas such a relation was not found in the oral contraceptives group, suggesting the presence of another factor (oral contraceptive use), which stimulates IL-6 production. Of particular interest is our finding that elevated IL-6 levels correlated significantly positively with elevated anti-β2-glycoprotein I antibody–IgG in patients who were users of oral contraceptives (but not overweight, n = 10) (r = 0.56, P < .05) CONCLUSION: The results suggest a new hypothesis that, in susceptible women, use of oral contraceptives induces production of IL-6, which stimulates production of anti-β2-glycoprotein I. Thus, the prothrombotic profile is aggravated and could facilitate occurrence of venous thromboembolism. This remains to be elucidated in further studies. LEVEL OF EVIDENCE: III

Vascular bed specific alterations in coagulation and fibrinolytic parameters in young women following myocardial infarction, lacunar cerebral infarction and deep vein thrombosis

The possible existence of distinctive, vascular bed specific alterations of coagulation and fibrinolytic parameters associated with three different types of thrombosis was investigated in young women (n = 68, <45 years at onset of the event) following myocardial infarction (MI) (n = 22), lacunar cerebral infarction (LACI) (n = 16), idiopathic deep vein thrombosis (VT) (n = 14) and venous thrombosis due to oral contraceptive use (n = 16) in the stable period after the acute thrombotic event. Coagulation and fibrinolytic parameters, as well as classical metabolic variables, were measured and compared with 52 age-matched, healthy controls. In MI women we observed elevated tissue type plasminogen activator (t-PA) antigen levels, which correlated significantly with parameters of the plurimetabolic syndrome. In LACI women we found elevated fibrinogen, which correlated with D-dimer, systolic blood pressure, smoking, and sedimentation rate. Prolonged euglobulin clot lysis time, elevated t-PA antigen, PAI-1 antigen and activity, which all correlated with parameters of the plurimetabolic syndrome, were found in women with idiopathic VT, who were also clearly obese but not in women in whom oral contraceptives were the triggering factor for VT. Our results showed not parallel, but different profiles of alterations in fibrinolytic and coagulation parameters in line with the prediction of a vascular bed specific thrombosis process.