A 42 year old male who is
known to have ankylosing spondylitis is admitted with a history of worsening
breathlessness and swelling of his body.
On examination you note that
he has gross oedema of his ankles, his pulse rate is 110 beats per minute, BP
120//80, he has bilateral pleural effusions, there is ascites.
Urine testing reveal
In this patient which one of
the following investigations would you arrange next?