My husband is suffering from depression how can dr diagonose this?

Several symptoms. Depressed mood and/or loss of interest or pleasure in life activities for at least 2 weeks and at least five of the following symptoms 1. Depressed mood most of the day. 2. Diminished interests 3. Significant weight loss or gain. 4. Insomnia or sleeping too much. 5. Agitation or psychomotor retardation 6. Fatigue 7. Guilt. 8. Poor concentration 9. Suicidal ideation.
Interview. Your husband's doctor can discuss with you and he the concerns for depression. There are a set list of criteria that physicians look for when making the diagnosis of depression. These criteria are listed in what is called the dsm IV manual. If your husband has symptoms that match the defined criteria, then he can be diagnosed with depression.