I found the key to coag was to know the principle of the test in question. Knowing how the test is performed will often guide you to the explanation for an abnormal result.
With that in mind, if you have found this site you almost certainly already know practical heamostasis - this is the go to website for laboratory haemostasis. I have not included much about the lab tests in this section, because if I did I would no doubt find myself plagiarising Dr Perry!
Other free online resources: