Ristocetin-induced platelet aggregation

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 (vWF) and exogenous antibiotic ristocetin added in a graded fashion.^[1] 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 (vWD) and Bernard-Soulier syndrome 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 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 ristocetin causes von Willebrand factor to bind the platelet receptor glycoprotein Ib (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 ^[2] (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)^[3]

References

↑ Coller BS, Gralnick HR (August 1977). "Studies on the mechanism of ristocetin-induced platelet adhesion. Effects of structural modification of ristocetin and vancomycin". The Journal of Clinical Investigation. 60 (2): 302–12. doi:10.1172/JCI108778. PMC 372370. PMID 17620.
↑ Riddell AF, Jenkins PV, Nitu-Whalley IC, McCraw AH, Lee CA, Brown, SA (January 2002). "Use of the collagen-binding assay for von Willebrand factor in the analysis of type 2M von Willebrand disease: a comparison with the ristocetin cofactor assay". British Journal of Haematology. 116 (1): 187–92. doi:10.1046/j.1365-2141.2002.03199.x. PMID 11841416.
↑ Pham A, Wang J. Bernard-Soulier syndrome: an inherited platelet disorder. Arch Pathol Lab Med (2007);131(12):1834-6.

Myeloid blood tests (CPT 85002–85999)

Clotting

CBC Platelet count Mean platelet volume vWF: Ristocetin-induced platelet aggregation

clotting factors:	Prothrombin time Partial thromboplastin time Thrombin time Activated clotting time

other/general:	coagulation Bleeding time animal enzyme Reptilase time Ecarin clotting time Dilute Russell's viper venom time Thromboelastography Thrombodynamics test

fibrinolysis:	Euglobulin lysis time D-dimer

Red blood cell indices

CBC	RBC count Hematocrit Hemoglobin

ratios:	Mean corpuscular hemoglobin Mean corpuscular hemoglobin concentration Mean corpuscular volume Red blood cell distribution width

Fetal hemoglobin:	Apt–Downey test Kleihauer–Betke test

Other	Reticulocyte index Haptoglobin Mentzer index

CFU-GM

Other

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