What initial laboratory tests are recommended for a 72-year-old woman presenting with flushing?

Laboratory Tests for Flushing in a 72-Year-Old Woman

For a 72-year-old woman presenting with flushing, the initial laboratory evaluation should include serum tryptase, plasma histamine, 24-hour urinary histamine metabolites, plasma-free metanephrine, urinary vanillylmandelic acid, serum serotonin, and urinary 5-hydroxyindoleacetic acid. 1

Initial Laboratory Panel

The following tests should be ordered to evaluate the cause of flushing:

Essential First-Line Tests

• Serum tryptase - Ideally obtained 1-2 hours after onset of symptoms to detect mast cell activation or anaphylaxis 1
• Complete blood count - To evaluate for polycythemia, anemia, or evidence of infection 1
• Comprehensive metabolic panel - Including liver and kidney function tests 1
• Thyroid function tests - Particularly TSH to rule out hyperthyroidism 1
• Fasting blood glucose - To evaluate for diabetes or reactive hypoglycemia 1

Specific Tests for Common Causes of Flushing

• Plasma histamine - Should be drawn within 30-60 minutes of symptom onset 1
• 24-hour urinary histamine metabolites - More useful if patient is seen hours after flushing episode 1
• Plasma-free metanephrine and urinary vanillylmandelic acid - To rule out pheochromocytoma 1
• Serum serotonin and urinary 5-hydroxyindoleacetic acid (5-HIAA) - To rule out carcinoid syndrome 1

Diagnostic Algorithm Based on Clinical Presentation

If flushing is episodic and associated with other symptoms:

• Hypotension, urticaria, or pruritus → Focus on tryptase, histamine tests (suspect anaphylaxis or mastocytosis)
• Headache, palpitations, anxiety → Focus on metanephrine, VMA (suspect pheochromocytoma)
• Diarrhea, wheezing, right-sided heart disease → Focus on serotonin, 5-HIAA (suspect carcinoid syndrome)
• Weight loss, night sweats → Consider additional tests for malignancy

If flushing occurs after meals:

• Add gastrin levels and consider vasoactive intestinal polypeptide (VIP) testing 1

Important Clinical Considerations

1. Timing of laboratory tests is critical - Serum tryptase peaks 60-90 minutes after symptom onset, while plasma histamine increases within 5-10 minutes but remains elevated only for 30-60 minutes 1

2. Medication review is essential - Many drugs can cause flushing, including niacin, nicotine, catecholamines, ACE inhibitors, and alcohol 1

3. Postmenopausal status - In a 72-year-old woman, postmenopausal flushing remains a consideration, though other causes should be ruled out 2

4. Avoid unnecessary testing - CA125 testing is not recommended as it is elevated in any condition causing ascites or pleural effusion and is very nonspecific 1

Pitfalls to Avoid

• Missing the timing window - Collecting samples too late after a flushing episode may yield false-negative results
• Incomplete evaluation - Failure to consider rare but serious causes like carcinoid syndrome or pheochromocytoma
• Premature diagnosis - Assuming menopausal flushing without ruling out other potentially serious conditions
• Overlooking medication causes - Not reviewing all medications, including over-the-counter supplements

By following this systematic laboratory approach, the underlying cause of flushing in this 72-year-old woman can be identified, allowing for appropriate treatment of the specific etiology.