Table 2.
Diagnostic approach to laboratory investigation (stage 1)
| Test | Assessment | Material |
|---|---|---|
| Blood count incl. platelet count and mean platelet volume (MPV), blood smear | Detection/exclusion of thrombocytopenia, indication of giant platelet disorders | EDTA-anticoagulated whole blood; citrate-anticoagulated whole blood in the case of EDTA-dependent pseudothrombocytopenia |
| Coagulation tests: PT, aPTT, TT, FXIII, reptilase time, tibrinogen concentration, vWF antigen, ristocetin-cofactor, collagen binding assay | Detection/exclusion of coagulation disorder. In case of prolonged PT/aPTT relevant factor assays should be performed, with inhibitor assay if indicated. A lupus inhibitor test should be performed in the view of isolated prolongation of the aPTT | plasma from citrated whole blood (citrated blood) |
| Standardized skin bleeding time | Prolonged bleeding time may be caused by drugs (e.g. acetylsalicylic acid) or is due to platelet function disorders | Mielke method, Duke method |
| Platelet function analyzer (PFA-100) | closure time is influenced by pre-analytical variables (platelet number, hematocrit, acetylsalicylic acid, and particularly vWF). Sensitivity is variable in congenital platelet disorders. The values are significantly prolonged in GT and BSS patients (closure time > 300 s with collagen/ADP and epinephrine/collagen cartridges). In SPD, HPS and QPS patients, PFA may be sensitive but false-negative results can often occur | citrated blood |
| Platelet aggregation using the Born method or impedance aggregometry with: ADP, collagen, arachidonic acid, epinephrine, ristocetin in concentration series and limiting concentrations | Several thrombocytopathies have typical aggregation patterns (table 3). Also platelet inhibitors (e.g. acetylsalicylic acid, clopidogrel, or GP Ilb/IIIa receptor antagonists) or other drugs such as high-dose ibuprofen and some antibiotics inhibit certain agonist-induced aggregations | platelet-rich plasma from citrated blood |
aPTT = Activated partial thromboplastin time; BSS = Bernard-Soulier syndrome; GT = Glanzmann thrombasthenia; HPS = Hermansky-Pudlak syndrome; PT = prothrombin time; QPS = Quebec platelet syndrome; SPD = storage-pool-disease; TT = thrombin time; vWF = von Willebrand factor.