The ristocetin-induced platelet aggregation (RIPA) is an ex vivo assay for live platelet function. It measures platelet aggregation with the help of

von Willebrand factor Von Willebrand factor (VWF) () is a blood glycoprotein involved in hemostasis, specifically, platelet adhesion. It is deficient and/or defective in von Willebrand disease and is involved in many other diseases, including thrombotic thrombocytopen ...

(vWF) and exogenous antibiotic

ristocetin Ristocetin is a glycopeptide antibiotic, obtained from ''Amycolatopsis lurida'', previously used to treat staphylococcal infections. It is no longer used clinically because it caused thrombocytopenia and platelet agglutination. It is now used so ...

added in a graded fashion. It is similar to the ristocetin cofactor assay but has the added benefit in that it helps in the diagnosis of type 2B/pseudo

von Willebrand disease Von Willebrand disease (VWD) is the most common hereditary blood-clotting disorder in humans. An acquired form can sometimes result from other medical conditions. It arises from a deficiency in the quality or quantity of von Willebrand factor ( ...

(vWD) and

Bernard–Soulier syndrome Bernard–Soulier syndrome (BSS) is a rare autosomal recessive bleeding disorder that is caused by a deficiency of the ''glycoprotein Ib-IX-V complex'' (GPIb-IX-V), the receptor for von Willebrand factor. The incidence of BSS is estimated to be ...

because it uses patient's live endogenous platelets, whereas ristocetin cofactor assay tests the function of only the vWF and not the platelets. Ristocetin cofactor assay uses the patient's platelet poor plasma (with vWF but no platelets) and adds ristocetin and exogenous formalin-fixed platelets which can passively agglutinate (but not actively aggregate, as they are dead). Formalin does not allow the extrinsic platelets to secrete the vWF of their α-granules, and thus only the activity of the intrinsic vWF is tested. In an unknown fashion, the antibiotic

causes von Willebrand factor to bind the platelet receptor

glycoprotein Ib Glycoprotein Ib (GPIb), also known as CD42, is a component of the Glycoprotein Ib-IX-V Receptor Complex, GPIb-V-IX complex on platelets. The GPIb-V-IX complex binds von Willebrand factor, allowing platelet adhesion and platelet plug formation at si ...

(GpIb), so when ristocetin is added to normal blood, it causes agglutination of fixed platelets or initiates the initial agglutination phase of aggregation of live platelets. The results of the ristocetin-induced platelet aggregation in some characteristic diseases are the following: * Type 1 vWD: hypoactive agglutination occurs (consistent with ristocetin cofactor assay results) * Type 2A vWD: hypoactive agglutination occurs (consistent with ristocetin cofactor assay results) * Type 2B vWD: hyperactive agglutination occurs (when the ristocetin cofactor assay is used, the agglutination is hypoactive) * Type 2M vWD: hypoactive agglutination occurs (consistent with ristocetin cofactor assay results) * Type 2N vWD: normal agglutination occurs (consistent with ristocetin cofactor assay results) * Type 3 vWD: no agglutination occurs (consistent with ristocetin cofactor assay results) * Pseudo-vWD: hyperactive agglutination occurs (when the ristocetin cofactor assay is used, the agglutination is hypoactive) * Bernard-Soulier syndrome: hypoactive agglutination occurs (when the ristocetin cofactor assay is used, the agglutination is normal)Pham A, Wang J. Bernard-Soulier syndrome: an inherited platelet disorder. Arch Pathol Lab Med (2007);131(12):1834-6. INTERPRETATION OF TEST RAT+ Ve= normal (gp1b & vWF present) RAT-ve=abnormal(gp1b & vWF absent)

References

{{Myeloid blood tests Blood tests