What lab tests are used to diagnose flushing?

From the Guidelines

To evaluate flushing, the most critical laboratory tests include a 24-hour urine collection for 5-hydroxyindoleacetic acid (5-HIAA) and serum chromogranin A, as these have the highest reliability and accuracy in diagnosing carcinoid syndrome, a potentially life-threatening condition 1. When assessing a patient with flushing, it is essential to consider various potential causes, including benign conditions like rosacea or medication effects, as well as more serious conditions such as carcinoid tumors or systemic mastocytosis.

• A complete blood count (CBC) and comprehensive metabolic panel (CMP) can provide valuable information on the patient's overall health status.
• Serum tryptase and histamine levels may help identify mastocytosis or other allergic reactions.
• If watery diarrhea accompanies flushing, testing for vasoactive intestinal peptide (VIP) may be necessary.
• In women, follicle-stimulating hormone (FSH) and estradiol levels can help determine if menopause is the cause of flushing.
• Thyroid function tests can identify hyperthyroidism, which may also cause flushing. The most recent and highest quality study 1 emphasizes the importance of measuring 5-HIAA and chromogranin A in diagnosing carcinoid syndrome, which can cause flushing, secretory diarrhea, and bronchoconstriction.
• The specificity of the urinary 5-HIAA test is close to 90%, making it a reliable diagnostic tool.
• Elevated serum levels of chromogranin A occur in 75% of carcinoid tumors and 60% of small cell lung cancers, making it a highly accurate biomarker. It is crucial to perform these tests during or shortly after a flushing episode, if possible, to ensure the most accurate results. By prioritizing these laboratory tests, healthcare providers can quickly and accurately diagnose the underlying cause of flushing, allowing for timely and effective treatment, and ultimately improving patient outcomes in terms of morbidity, mortality, and quality of life.

From the Research

Lab Tests for Flushing

To diagnose the cause of flushing, several lab tests can be performed. The following are some of the tests that can be used:

• Blood tests to check for elevated levels of certain hormones, such as serotonin, histamine, and catecholamines 2, 3, 4
• Urine tests to check for elevated levels of certain metabolites, such as 5-hydroxyindoleacetic acid (5-HIAA) 5, 6
• Imaging tests, such as computed tomography (CT) or magnetic resonance imaging (MRI) scans, to check for tumors or other abnormalities 3, 4
• Biopsy to check for mast cell activation syndrome or other conditions 3, 4

Conditions that Cause Flushing

Flushing can be caused by several conditions, including:

• Carcinoid syndrome, a condition caused by a neuroendocrine tumor that produces excess serotonin 2, 3, 5, 6
• Mastocytosis, a condition caused by an accumulation of mast cells in the body 2, 3, 4
• Pheochromocytoma, a condition caused by a tumor of the adrenal gland that produces excess catecholamines 2, 3, 4
• Menopausal hot flushes, a common symptom of menopause 2, 3
• Other conditions, such as VIPoma, medullary thyroid cancer, renal cell carcinoma, and mast cell activation syndrome 3, 4

Diagnostic Approach

A systematic approach is needed to diagnose the cause of flushing, including:

• Taking a thorough medical history and performing a physical examination 2, 3, 4
• Performing lab tests and imaging studies to rule out underlying conditions 2, 3, 5, 6, 4
• Using a diagnostic algorithm to guide the evaluation process 2, 4