What labs should be obtained for a patient presenting with dysgeusia (metal taste in the mouth)?

Laboratory Evaluation for Metallic Taste (Dysgeusia)

For a patient presenting with metallic taste in the mouth, obtain a complete blood count (CBC), comprehensive metabolic panel (CMP), serum iron studies (including ferritin), and consider zinc and copper levels if initial workup is unrevealing.

Essential Initial Laboratory Tests

Core Metabolic and Hematologic Assessment

• Complete Blood Count (CBC) is mandatory to identify iron deficiency anemia, which was found to be causative in 28% of hypogeusia patients and is associated with elevated taste thresholds that normalize with treatment 1
• Comprehensive Metabolic Panel (CMP) including electrolytes, liver enzymes, and renal function tests should be obtained, as chronic kidney disease and hepatic dysfunction are established systemic causes of dysgeusia 2, 3
• Serum iron studies (iron, ferritin, total iron-binding capacity) are critical because iron deficiency was identified as the cause in 7 of 25 patients with taste abnormalities, and correction of iron deficiency led to resolution of symptoms 1

Additional Targeted Testing

• Serum zinc levels should be measured using flameless atomic absorption spectrophotometry if initial workup is negative, though notably, zinc deficiency was not found in dysgeusia patients in controlled studies despite historical emphasis on this mechanism 4, 1
• Serum copper levels can be checked concurrently with zinc, though copper deficiency was not observed in any patients with taste abnormalities in systematic evaluation 1
• Blood glucose or HbA1c should be obtained to screen for diabetes mellitus, which is a recognized systemic cause of dysgeusia 3

Clinical Context and Diagnostic Algorithm

Medication Review Takes Priority

• Comprehensive medication review is essential before extensive laboratory testing, as drug-induced dysgeusia is extremely common and affects 35 different medications including ACE inhibitors, chemotherapeutic agents, antibiotics, and antihistamines 5
• Drug-induced dysgeusia typically resolves completely within 2 months of medication cessation, making this the most reversible cause 1, 5

Oral Cavity Examination

• Oral candidiasis assessment through clinical examination and Candida culture is necessary, as oral candidiasis was causative in 24% of hypogeusia cases and 21% of dysgeusia cases 1
• Salivary flow rate measurement should be performed, as hyposalivation (xerostomia) was identified in 24% of hypogeusia patients and contributes to taste dysfunction 1

Important Clinical Distinctions

Hypogeusia vs. Dysgeusia Laboratory Patterns

• Hypogeusia (decreased taste sensation) is typically accompanied by elevated taste thresholds and responds to treatment of underlying causes like iron deficiency, with thresholds normalizing as symptoms improve 1
• Dysgeusia (abnormal/metallic taste) shows no elevation or depression of taste thresholds on objective testing and is more commonly associated with psychiatric distress (57% of cases) or medication effects rather than nutritional deficiencies 1

Common Pitfalls to Avoid

• Do not assume zinc deficiency is the primary cause without evidence, as serum zinc and copper levels were normal in all patients studied despite historical emphasis on zinc supplementation 1
• Do not order extensive trace element panels as first-line testing; focus on CBC and iron studies first, as iron deficiency is the only nutritional deficiency consistently associated with reversible taste abnormalities 1
• Do not overlook psychiatric causes, particularly in patients with dysgeusia (abnormal taste) rather than hypogeusia (decreased taste), as psychiatric distress was the leading cause in 57% of dysgeusia cases 1

Systematic Conditions Requiring Screening

• Chronic kidney disease should be evaluated through the CMP, as uremia is a well-established cause of dysgeusia 3
• Respiratory infections including COVID-19 should be considered in the appropriate clinical context, as taste disorders are among the earliest symptoms 6
• Diabetes mellitus screening is warranted given its association with gustatory dysfunction 3