Whether you are offered the option of an urine test instead of samples of your hair being used for drug screening is subject to the policies of your possible employer. If you simply do not have enough hair for a sample to be taken for drug screening, it will be readily apparent to the person doing the testing.I would think that under the circumstances, if you do not have enough hair for a sample for drug screening, then an urine sample would most likely be the suggested course.As a safeguard, you might bring some medical reports about your condition explaining your minimal amount of hair.Good luck in getting the job.