There are multiple classification systems designed to assist clinicians with the diagnosis of depression. Both the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM-5) and the World Health Organization’s International Classification of Diseases (ICD-11) criteria are used by clinicians to assist with diagnosis of depression. Both DSM-5 and ICD-11 classify depression by severity, duration, and subtypes, all of which can impact treatment decisions.

In the United States, mental health professionals are more likely to rely on and be familiar with the DSM-5 criteria and classifications, because the DSM guidebook is specifically tailored to cover mental health disorders as they are experienced and treated in the United States.

The DSM-5 lists the following criteria for the diagnosis of major depressive disorder (MDD)¹:

1. Five (or more) of the following symptoms are present for a 2-week duration and are a change from the previous functioning level. The criteria must occur nearly every day.

• At least 1 of the symptoms is either (a) depressed mood or (2) loss of interest or pleasure.
•  Depressed mood lasting most of the day. This includes subjective observation (reporting feeling sad, empty, and/or hopeless) or observations made by others around the individuals (such as increased tearfulness).
• Markedly decreased interest or pleasure in all, or nearly all, activities that lasts for most of the day.
• Significant weight loss or weight gain, not attributed to other sources such as dieting, or decrease in appetite. This is a weight change of more than 5% in body weight.
• Insomnia or hypersomnia.
• Psychomotor agitation or retardation that is observable by others around the individual (not just a feeling of being slowed down or agitated).
• Fatigue or loss of energy.
•  Feelings of worthlessness or excessive or inappropriate guilt.
•  Diminished ability to think and concentrate or indecisiveness.
• Recurrent thoughts of death, suicidal ideation, or a suicide attempt

2.    The symptoms cause clinical distress and impair an individual’s social and occupational areas of functioning.
3.    The symptoms are not attributable to the use of substances or other medical conditions.
4.    These symptoms cannot be attributed to other disorders such as schizoaffective disorder, schizophrenia, schizophreniform disorder, delusional disorder, unspecified schizophrenia spectrum, or other psychotic disorders.
5.    The individual has never experienced a manic or hypomanic episode.

Criteria 1 through 3 make up the criteria for a major depressive episode.¹ The most common symptoms patients experience when presenting are insomnia and fatigue.¹ Psychomotor symptoms are much less common, but their presence indicates a greater overall severity of MDD.¹ Health care providers should conduct a complete diagnostic evaluation, including bloodwork, prior to diagnosis. Medical conditions such as thyroid problems or vitamin deficiencies can cause depression-like symptoms.²

Timely diagnosis of patients with depression can have an important impact on patient outcomes. Patients with MDD have a higher mortality rate than those without depression, largely attributed to an increased suicide rate in this population.¹ Individuals with depression admitted to nursing homes are also more likely to die within the first year than others not diagnosed with depression.¹ Therefore, proper identification and management of MDD is critical to improving morbidity and mortality in affected patients.

References:
1.    American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 5th ed. 2013. doi:10.1176/appi.books.9780890425596
2.    What is depression? American Psychiatric Association. Updated October 2020. Accessed December 6, 2022. https://www.psychiatry.org/patients-families/depression/what-is-depression