Social Security will consider any existing medical records when deciding your claim. Your initial application to Social Security will indicate the date that you have alleged to be your Onset date of disability. For example, if you note that April 1, 2013 is the date when you became disabled and no longer able to work, social security will review medical records one year prior to the alleged onset date of April 1, 2013. Medical records that reflect ongoing treatment from this date will become the deciding factor for your claim. It is very important that your medical records reflect the condition(s) in which you are applying for benefits.
More often than not, social security will consider other conditions that may exacerbate your primary condition. An example of this would be of listing diabetes as a primary condition and the secondary condition listed as uncontrolled high blood pressure. Upon review, social security will consider the various treatments to control the high blood pressure. This consideration could weigh heavily on the outcome of your claim. Medical records that show a lack of treatment or diagnosis would surely result in a denial.
Lastly and most importantly, having a supportive doctor will increase your chances of a favorable decision. Social Security gives more weight to the opinion of your treating physician than that of a non-physician. So the rule of thumb is to make sure that you are detail in your description of symptoms that you may be experiencing from your condition(s).