Thyroid Function Test (TFT) is the Most Appropriate Initial Investigation
For a patient presenting with depression, loss of appetite, social isolation, anxiety, and medication non-compliance, thyroid function testing should be performed first to exclude medical causes before attributing symptoms to primary psychiatric illness. 1
Rationale for Prioritizing Thyroid Screening
Depression and anxiety guidelines consistently emphasize treating medical causes of depressive symptoms before proceeding with psychiatric interventions. 1 Thyroid dysfunction—both hypothyroidism and hyperthyroidism—can present with the exact constellation of symptoms described: depression, anxiety, appetite changes, social withdrawal, and cognitive impairment that manifests as medication non-compliance. 1
The medication non-compliance in this patient may reflect underlying cognitive impairment or apathy from undiagnosed thyroid disease rather than primary psychiatric pathology. 1 This is a critical diagnostic consideration that must be excluded before initiating psychiatric treatment, as thyroid dysfunction is readily treatable and can fully explain the symptom presentation. 1
Why Not the Other Options
Urine Drug Test - Not the Priority
While the patient expresses intent to use marijuana for stress relief, this does not constitute current substance use requiring immediate toxicology screening. 2 The desire to use marijuana should not be dismissed, as this increases anxiety and reduces trust in healthcare providers, but it does not warrant prioritization over excluding treatable medical causes. 2
Research evidence on marijuana use in depression is mixed and does not support it as a diagnostic priority:
- Non-medical marijuana use in depressed patients is associated with worse depression symptom improvement and higher suicidal ideation over time 3
- However, when confounders are controlled, longitudinal studies show no significant association between cannabis use and incident depression or anxiety 4
Complete Blood Count - Secondary Investigation
While anemia can contribute to fatigue and depressive symptoms, it does not explain the full symptom constellation including anxiety, social isolation, and medication non-compliance. 5 CBC would be appropriate as part of a comprehensive workup for fatigue after thyroid dysfunction is excluded. 5
Pulmonary Function Test - Not Indicated
There is no clinical indication for pulmonary function testing in this presentation. The patient's symptoms do not suggest respiratory pathology.
Clinical Approach After Thyroid Screening
Once thyroid dysfunction is excluded with a sensitive TSH assay 1, proceed with:
- Validated psychiatric screening tools: Use PHQ-9 for depression (scores ≥10 indicate moderate depression) and GAD-7 for anxiety (scores ≥10 indicate moderate anxiety) 5, 2
- Immediate suicide risk assessment: Screen for suicidal ideation first, as suicide risk is elevated in patients with depression and anxiety 2
- Assessment of medication non-compliance barriers: Explore specific reasons including fear of side effects, cost, denial of illness, or frustration with polypharmacy 2
- Evaluation for comorbid conditions: 50-60% of patients with anxiety disorders have comorbid depressive symptoms 2
Common Pitfalls to Avoid
Do not prematurely diagnose primary psychiatric illness without excluding thyroid dysfunction, which can fully explain the symptom constellation. 1 This is the most critical error in this clinical scenario, as it leads to inappropriate psychiatric treatment while missing a readily treatable medical condition.
Do not provide or deny sick leave without proper medical evaluation and referral—anxiety and depression with documented functional impairment represent genuine medical conditions requiring appropriate assessment. 2