First, I need to confirm if Tejinder Singh has written a hematology book. A quick search in my mind shows that there's a book titled "Textbook of Hematology" by various authors. Maybe Tejinder Singh is another author or a contributor. However, since I don't have specific knowledge about an author named Tejinder Singh in this context, there's a chance they might be misremembering the name or it's an obscure source.