He looked to be in good health, judging by that photo from the summer.
Here's a snippet from an article in late September:
Yushchenko's health worries began on 5 September, when the former prime minister began to fall sick. Five days later, he was transported to a private clinic in Vienna, Rudolfinerhaus. By this time he was gravely ill, with a whole range of baffling symptoms. Nikolai Korpan was Yushchenko's chief physician in Vienna. He describes the symptoms in a telephone interview with RFE/RL.
"He had acute pancreatitis [inflammation of the pancreas], he had acute gastritis, he had acute proctocolitis, acute myositis [eds: muscle inflammation], acute paralysis of the facial nerve and he was [describing] different pain symptoms, for example in the area of the abdominal cavity and the thorax cavity, the breast cavity," Korpan says.
http://www.doctorsiegel.com/radio_free_europe.htm
I think you're right, and I certainly hope they did hair and fingernail analysis.
From what I'm googling, that may be the only way to determine if he was poisoned with arsenic, since it leaves the body after a few days, but if done within 6 to 12 months those particular tests can help.
You would think the docs would have tested for that, wonder if they did.