Investigations
1st investigations to order
clinical diagnosis
Test
Major depression: ≥5 of the following symptoms have been present during the same 2-week period and represent a change from previous functioning. At least one of the symptoms is either depressed mood or loss of interest or pleasure: depressed mood most of the day, nearly every day as self-reported or observed by others; markedly diminished interest or pleasure in all or almost all activities most of the day, nearly every day; significant weight loss when not dieting, weight gain or decrease or increase in appetite nearly every day; insomnia or hypersomnia nearly every day; psychomotor agitation or retardation nearly every day; fatigue or loss of energy nearly every day; feelings of worthlessness or excessive or inappropriate guilt nearly every day; diminished ability to think or concentrate, or indecisiveness, nearly every day; recurrent thoughts of death, recurrent suicidal ideation without a specific plan, a specific suicide plan, or a suicide attempt.[1]
In addition, these symptoms: cause functional impairment (e.g., social, occupational); are not related to substance abuse, medication side effects, or another medical condition; are not related to a grief reaction.
Women who have clinically significant changes in mood along with other depressive symptoms, linked to the menstrual cycle, may warrant a diagnosis of premenstrual dysphoria. Patients who have depressive symptoms attributable to another cause, such as psychoactive drugs, medication side effects, or medical illness, may be diagnosed with specific substance-induced or medication-related depressive symptoms or depression secondary to a specified somatic medical condition, respectively. Otherwise, clinically significant depression where the symptoms fall short of meeting full DSM-5-TR criteria in number, duration, or severity can be diagnosed as either 'other specified depressive disorder' (where the reason for falling short of criteria is given: for example, 'brief' or 'short-duration' or 'insufficient symptoms') or 'unspecified depressive disorder' where the reason is not stated.
Persistent depressive disorder: the patient has had depressed mood, for most of the day, for more days than not, for ≥2 years.[1]
Subthreshold (minor) depression is not defined in DSM-5-TR, but may apply to those with 2-4 depressive symptoms, including either sad mood or anhedonia, for at least 2 weeks.[5][6]
Result
ICD-11 or DSM-5-TR diagnostic criteria depending on the depressive subcategory
metabolic panel
Test
Provides baseline and may reveal metabolic disturbance.
Result
normal
FBC
Test
Other causes of fatigue such as anaemia should be ruled out.
Result
normal
thyroid function tests
Test
An elevated serum thyroid-stimulating hormone level suggests hypothyroidism.
Result
normal
Patient Health Questionnaire-2 (PHQ-2)
Test
The PHQ-2 is derived from the Primary Care Evaluation of Mental Disorders (PRIME-MD) tool and quickly and accurately screens for depression with only two questions: 'Over the past 2 weeks, have you felt down, depressed, hopeless?' and 'over the past 2 weeks, have you felt little interest or pleasure in doing things?'[135] [ Depression (any) Screening by a Two Item PHQ-2 Opens in new window ]
A positive response to either question warrants a thorough review of diagnostic criteria or an equivalent tool.
Result
positive result screens for depression in primary care
Patient Health Questionnaire-9 (PHQ-9)
Test
The PHQ-9 can be used as a diagnostic and disease management tool. The PHQ-9 is a 9-item depression questionnaire that reflects the DSM-5-TR criteria. It classifies current symptoms on a scale of 0 (no symptoms) to 4 (daily symptoms). It has been validated for use in primary care settings. Repeating the PHQ-9 during treatment allows the clinician to objectively monitor response to therapy.
Result
positive result screens for depression in primary care
Edinburgh Postnatal Depression Scale
Test
US and UK guidelines stress the importance of routinely assessing patients for depression during the perinatal period.[136][137] The Edinburgh Postnatal Depression Scale is a 10-item questionnaire for women in the perinatal period. A score of ≥10 suggests depression; however, clinicians should be mindful of individual patient circumstances (e.g., education and culture) that might impact scoring.[138][139][140] Although it does not assess the severity of depression, it does assess for suicidal ideation. Edinburgh Postnatal Depression Scale Opens in new window
See Postnatal depression.
Result
positive result screens for depression in postnatal period
Geriatric Depression Scale
Test
The short form contains 15 yes/no questions. [ Geriatric Depression Scale Opens in new window ]
This scale does not assess the severity of symptoms.[141][142]
Result
>5 suggests depression; >10 strongly suggests depression
Cornell Scale for Depression in Dementia
Test
This scale is a 19-item questionnaire intended for geriatric patients with dementia. Cornell Scale For Depression in Dementia Opens in new window
This scale does not assess the severity of symptoms.[143]
Result
>10 suggests probable depression; >18 indicates definite depression
Investigations to consider
24-hour free cortisol
Test
Elevated 24-hour urinary free cortisol level suggests Cushing's disease.
Result
normal
vitamin B12
Test
Vitamin B12 deficiency is associated with macrocytic anaemia, paraesthesia, numbness, and impaired memory.
Result
normal
folic acid
Test
Patients with depression have been found to have lower levels of serum folate than people without a psychiatric diagnosis, and than non-depressed psychiatric patients.[144]
Result
normal
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