This patient has 2 concentrations taken 2 hours apart.

When plotted on the graph it is clear that the fall in paracetamol concentration is slower than the nomogram line. This suggests that t that hepatotoxicity is likely.

This technique is unlikely to have validity for short half-lives, when the samples are taken after 12 hours, or when the concentrations are low.

If the samples are collected too close together lab error and variation will make the interpretation more unreliable. Ideally you should allow a number of lives to have elapsed.