Which of the following is NOT a coagulation disorder?

Pneumonia is not classified as a coagulation disorder; it is primarily a respiratory infection that affects the lungs. Coagulation disorders are conditions that result from abnormalities in the blood coagulation process, leading to issues such as excessive bleeding or inappropriate clotting.

In contrast, the other options listed are all related to coagulation problems. Hemolytic uremic syndrome can lead to platelet consumption and alterations in coagulation factors, immune thrombocytopenic purpura involves low platelet counts which can affect normal clotting, and von Willebrand disease is a genetic disorder affecting the blood's ability to clot properly due to a deficiency or dysfunction of von Willebrand factor. Understanding these distinctions helps clarify the classification of various disorders and their physiological implications.