Is the RIPA (Ristocetin-Induced Platelet Aggregation) test accurate during pregnancy?

RIPA Test Accuracy in Pregnancy

The Ristocetin-Induced Platelet Aggregation (RIPA) test is not accurate during pregnancy and should not be used alone to diagnose disorders of primary hemostasis such as von Willebrand disease in pregnant women. 1

Limitations of RIPA in Pregnancy

The RIPA test has significant limitations during pregnancy for several reasons:

• Bypasses primary hemostasis: According to the Journal of Thrombosis and Haemostasis, tests like RIPA use reagents that activate coagulation while bypassing primary hemostasis, making them insensitive to platelet dysfunction and disorders affecting endothelial adherence 1

• Cannot detect von Willebrand disease: RIPA cannot adequately assess the contribution of endothelium to coagulation, making it unable to reliably detect von Willebrand disease or other conditions affecting platelet adherence to the endothelium 1

• Physiological changes in pregnancy: Pregnancy causes significant changes in von Willebrand factor (VWF) levels, which can affect RIPA test results and interpretation 2

Why RIPA Is Problematic During Pregnancy

1. Pregnancy alters VWF levels: VWF antigen levels increase throughout normal pregnancy, with the VWF:Ag/factor VIII:C ratio remaining close to 1.0 throughout pregnancy 2

2. Inconsistent results: The test can yield inconsistent or unreliable results, especially in conditions where blood viscosity is altered, which commonly occurs during pregnancy 1

3. Hematocrit influence: Hematocrit influences RIPA test results, which is problematic since pregnancy is often associated with physiologic anemia 1

Alternative Testing Approaches

For diagnosing disorders of primary hemostasis during pregnancy:

• Multiple test approach: Supplement with more sensitive platelet function tests when evaluating for von Willebrand disease or platelet dysfunction 1

• Standard laboratory analysis: This provides more specific information on factors involved in impaired hemostasis compared to RIPA 1

• Peripheral blood smear examination: This should be performed to exclude other causes of thrombocytopenia in pregnant women 3

Clinical Implications

• Misdiagnosis risk: Relying solely on RIPA during pregnancy could lead to misdiagnosis of von Willebrand disease or other platelet disorders 1

• Treatment decisions: Accurate diagnosis is crucial because therapy for von Willebrand disease varies according to subtype 4

• Bleeding risk assessment: For pregnant women with suspected von Willebrand disease, bleeding complications are more frequent when levels of von Willebrand ristocetin cofactor assay and factor VIII levels are <50 IU/dL 4

Monitoring Recommendations

For pregnant women with suspected bleeding disorders:

• Monitor platelet count trends: Not just absolute values, as recommended by the American Society of Hematology 3

• Increase monitoring frequency: Especially as delivery approaches and in the third trimester 3

• Multidisciplinary approach: Collaboration among obstetrician, hematologist, anesthesiologist, and neonatologist is essential 3

The British Society for Hematology and American Society of Hematology both recommend against relying solely on tests like RIPA that cannot adequately assess platelet function during pregnancy 1, 3.