If you notice any possible symptoms and especially if you have any risk factors. Your doctor may suspect vitamin C deficiency after asking you careful questions about your diet and listening to the symptoms that you have. A blood test can be taken to measure vitamin C levels and may help to confirm the diagnosis.
 
Your doctor may also suggest some other blood tests to check for other deficiencies in your diet. For example, vitamin C is also needed for the absorption of iron from food. 
 
Therefore, iron deficiency often occurs in people who are deficient in vitamin C. 
