Is the activated partial thromboplastin time suitable to screen for von Willebrand factor deficiencies?

Effects of Thyroid Function on Hemostasis, Coagulation, and Fibrinolysis: A Mendelian Randomization Study

Background: Untreated hypothyroidism is associated with acquired von Willebrand syndrome, and hyperthyroidism is associated with increased thrombosis risk. However, the causal effects of thyroid function on hemostasis, coagulation, and fibrinolysis are unknown. Methods: In a two-sample Mendelian randomization (MR) study with genome-wide association variants, we assessed causality of genetically predicted hypothyroidism (N = 134,641), normal-range thyrotropin (TSH; N = 54,288) and free thyroxine (fT4) (N = 49,269), hyperthyroidism (N = 51,823), and thyroid peroxidase antibody positivity (N = 25,821) on coagulation (activated partial thromboplastin time, von Willebrand factor [VWF], factor VIII [FVIII], prothrombin time, factor VII, fibrinogen) and fibrinolysis (D-dimer, tissue plasminogen activator [TPA], plasminogen activator inhibitor-1) from the CHARGE Hemostasis Consortium (N = 2583-120,246). Inverse-variance-weighted random effects were the main MR analysis followed by sensitivity analyses. Two-sided p < 0.05 was nominally significant, and p < 0.0011[ = 0.05/(5 exposures × 9 outcomes)] was Bonferroni significant for the main MR analysis. Results: Genetically increased TSH was associated with decreased VWF [β(SE) = -0.020(0.006), p = 0.001] and with decreased fibrinogen [β(SE) = -0.008(0.002), p = 0.001]. Genetically increased fT4 was associated with increased VWF [β(SE) = 0.028(0.011), p = 0.012]. Genetically predicted hyperthyroidism was associated with increased VWF [β(SE) = 0.012(0.004), p = 0.006] and increased FVIII [β(SE) = 0.013(0.005), p = 0.007]. Genetically predicted hypothyroidism and hyperthyroidism were associated with decreased TPA [β(SE) = -0.009(0.024), p = 0.024] and increased TPA [β(SE) = 0.022(0.008), p = 0.008], respectively. MR sensitivity analyses showed similar direction but lower precision. Other coagulation and fibrinolytic factors were inconclusive. Conclusions: In the largest genetic studies currently available, genetically increased TSH and fT4 may be associated with decreased and increased synthesis of VWF, respectively. Since Bonferroni correction may be too conservative given the correlation between the analyzed traits, we cannot reject nominal associations of thyroid traits with coagulation or fibrinolytic factors.

Clinical relevance of isolated prolongation of the activated partial thromboplastin time in a cohort of adults undergoing surgical procedures

BACKGROUND

Coagulation screening prior to surgery is performed routinely worldwide to identify patients at risk of bleeding during the procedure. Evidence from medical and surgical literature suggests that the activated partial thromboplastin time (aPTT) alone is suitable for predicting individual bleeding risk during surgery and it is current practice in our hospital to measure this parameter.

MATERIALS AND METHODS

We retrospectively reviewed aPTT ratio results in 8,069 consecutive adult subjects undergoing elective surgery from January 1 to December 31, 2014 to confirm the validity of this approach.

RESULTS

In 7,606 patients (94.2%) the aPTT ratio was within the normal range while it was abnormal in 463 (5.8%). Out of these 463, 223 aPTT ratios were between 1.2 and 1.3 and we considered these results not worthy enough of further investigations. In 240 patients the aPTT ratio was higher than 1.3; in the vast majority of these cases (201/240; 83%) this abnormality was associated with oral anticoagulant treatment. Seventeen of the other 39 cases underwent detailed investigations which revealed lupus anticoagulant (n=7), decompensated chronic liver disease (n=4), factor XII deficiency (n=3), mild combined reduction of FXI and FXII (n=1) and mild haemophilia A (n=2). The other 22 patients underwent successful surgery without further investigation.

DISCUSSION

Our results from a pre-surgical setting seem to confirm the low prevalence of coagulation defects in the general population. Increased aPTT ratios were mainly attributable to oral anticoagulant therapy, with a few cases caused by mild, clinically irrelevant clotting factor deficiencies. A carefully taken personal history, including medications (i.e. oral anticoagulants) and/or previous bleeding symptoms seem more useful than coagulation screening tests to predict the risk of bleeding.

A genetic association study of activated partial thromboplastin time in European Americans and African Americans: the ARIC Study

Reduced activated partial thromboplastin time (aPTT) is a risk marker for incident and recurrent venous thromboembolism (VTE). Genetic factors influencing aPTT are not well understood, especially in populations of non-European ancestry. The present study aimed to identify aPTT-related gene variants in both European Americans (EAs) and African Americans (AAs). We conducted a genetic association study for aPTT in 9719 EAs and 2799 AAs from the Atherosclerosis Risk in Communities (ARIC) study. Using the Candidate Gene Association Resource (CARe) consortium candidate gene array, the analyses were based on ∼50 000 SNPs in ∼2000 candidate genes. In EAs, the analyses identified a new independent association for aPTT in F5 (rs2239852, P-value = 1.9 × 10(-8)), which clusters with a coding variant rs6030 (P-value = 7.8 × 10(-7)). The remaining significant signals were located on F5, HRG, KNG1, F11, F12 and ABO and have been previously reported in EA populations. In AAs, significant signals were identified in KNG1, HRG, F12, ABO and VWF, with the leading variants in KNG1, HRG and F12 being the same as in the EAs; the significant variant in VWF (rs2229446, P-value = 1.2 × 10(-6)) was specific to the AA sample (minor allele frequency = 19% in AAs and 0.2% in EAs) and has not been previously reported. This is the first study to report aPTT-related genetic variants in AAs. Our findings in AAs demonstrate transferability of previously reported associations with KNG1, HRG and F12 in EAs. We also identified new associations at F5 in EAs and VWF in AAs that have not been previously reported for aPTT.

Higher morning serum cortisol level predicts increased fibrinogen but not shortened APTT

BACKGROUND

There is emerging evidence that serum cortisol might be independently associated with prothrombotic activity, suggesting that increased cortisol levels might finally contribute to the pathogenesis of atherosclerotic disorders. Since hypercoagulability is principally sustained by either defective naturally occurring anticoagulant mechanisms or to heightened coagulation factors, most of which are cumulatively explored by the activated partial thromboplastin time (APTT), the present investigation was designed to asses the potential relationship between morning serum cortisol, APTT and fibrinogen in a general population of healthy outpatients.

METHODS

We performed a retrospective analysis on the database of our Laboratory Information System to retrieve results of morning serum cortisol, APTT and fibrinogen, which were performed on consecutive outpatients referred by general practitioners for routine blood testing over the previous 2 years.

RESULTS

Cumulative results for morning serum cortisol, APTT and fibrinogen were retrieved for 302 adults >35 years old (M/F = 61/90; age 49 +/- 13 years; range 35-79). A statistically significant increased concentration of fibrinogen was observed in subject with morning serum cortisol values above the upper limit of the reference range (P < 0.001), whereas the concentration of APTT was not significantly different between the two subgroups of subjects with normal and increased morning serum cortisol (P = 0.432). This difference remained statistically significant even after adjusting for age and sex. In multivariable linear regression analysis, the concentration of fibrinogen, but not the value of the APTT, was significantly associated with morning serum cortisol.

CONCLUSIONS

The results of this retrospective investigation confirm that baseline cortisol levels might predict higher fibrinogen in the general population. This potential biological interrelationship deserves further scrutiny for the potential implications on prediction and prevention of the cardiovascular risk.