There are many different ways of looking at nutrition via blood tests such as iron levels, calcium levels and vitamin levels. There are many ways of testing for absorption problems such as Coeliac disease and there are many ways of looking for inflammation indirectly via blood tests. We can also look for anaemia and inflammation of the liver and the pancreas. Blood tests for allergies can also be used but these usually help in looking for the acute type of allergy such as that which occurs with rashes, asthma, hay fever rather than necessarily helping with the longer term delayed reactions associated with gut related food allergies. Although these tests if positive can be helpful, if they are negative they are less helpful.