This man is an excellent option, if you need some investigations done. Sadly, his deerstalker has never been washed, and is highly infected with MRSA
Why am I investigating?
Sometimes a good history plus an examination is not the solution to the case. Your next step is to do some investigation. This can help whittle down your differential diagnosis.
What can I do?
The main ones are blood tests, and imaging.
The big ones to know are FBC, Clotting, U+Es, TFTs and LFTs. If you work out what they mean, that's probably all the blood tests you'll ever need to know, except for ESR and CRP (inflammatory markers).
Another important test to learn about is the arterial blood gas, or ABG
The big, big one is the Chest Xray. Learn ECG too.
Aside from this, there is a vast list, including Andiography, CT, MRI, Ultrasound and others. Visit the Imaging page for more.