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Section 7.1 Laboratory

Laboratory Report #24

Date

Collection Date: July 26, 2022
Report Date: August 2, 2022

Laboratory

Quest Diagnostics

Performing Laboratory:
Mayo Clinic Laboratories
Rochester, Minnesota

Ordering Physician

Dr. Maryam Saifi

Report Type

Specialized Allergy / Mast Cell Evaluation

Laboratory testing included:

  • 24-Hour Urine N-Methylhistamine
  • 24-Hour Urine Creatinine
  • Urine Volume
  • Collection Duration

Original Report

PDF: Quest Diagnostics – July 26, 2022 (24-Hour Urine N-Methylhistamine)

One-Page Summary

Purpose of Testing

This specialized laboratory evaluation was performed as part of an investigation for mast cell activation disorders. N-Methylhistamine is a breakdown product of histamine and is measured in a 24-hour urine collection to help identify excessive mast cell activation. This study complements the serum tryptase test performed during the same evaluation and provides another method for assessing mast cell-related disease.

Major Findings

24-Hour Urine N-Methylhistamine

Result

  • 109 mcg/g Creatinine

Reference Range:

  • 30–200 mcg/g Creatinine

Interpretation

The urinary N-Methylhistamine level was well within the normal reference range.

This finding indicates:

  • No laboratory evidence of increased histamine production.
  • No biochemical evidence of excessive mast cell activation at the time of testing.
  • Additional evidence against mast cell activation syndrome (MCAS) or systemic mastocytosis as the cause of previous symptoms.

When interpreted together with the normal serum tryptase obtained during the same evaluation, the laboratory evidence does not support a mast cell disorder.

Collection Quality

Twenty-Four-Hour Urine Collection

  • Collection Duration: 24 hours
  • Urine Volume: 2,200 mL
  • 24-Hour Creatinine: 1,276 mg/24 hr
  • Urine Creatinine Concentration: 58 mg/dL

Interpretation

The 24-hour urine collection appears complete and adequate for interpretation. The urine creatinine excretion falls within the laboratory reference range, supporting the reliability of the N-Methylhistamine result.

Clinical Significance

This report represents another step in the systematic search for the cause of your 2021 inflammatory illness.

By July 2022, your physicians had investigated several possible explanations, including:

  • Rheumatoid arthritis
  • Lupus
  • Sjögren’s syndrome
  • Bloodstream infection
  • Muscle disease
  • Mast cell disorders

The normal urinary N-Methylhistamine level adds another important piece of evidence indicating that mast cell activation was unlikely to be responsible for your illness.

Overall Interpretation

This specialized Mayo Clinic laboratory evaluation demonstrated a normal 24-hour urinary N-Methylhistamine level. The normal result, together with the previously normal serum tryptase, provides reassuring evidence against mast cell activation syndrome or systemic mastocytosis. The urine collection was complete and adequate, increasing confidence in the validity of the results. This report is another valuable diagnostic exclusion in the comprehensive investigation of your unexplained systemic inflammatory illness.

Longitudinal Significance

This report contributes to:

  • Allergy / Immunology Evaluation
  • Mast Cell Disorder Evaluation
  • Differential Diagnosis Archive
  • Rheumatology Consultation Summary
  • Systemic Inflammatory Illness Timeline
  • Medical History Timeline

Clinical Importance

⭐⭐⭐ Diagnostic Exclusion Study

Although this report contains only one specialized diagnostic marker, it is clinically valuable because it provides additional evidence against mast cell activation disorders as a cause of your previous inflammatory illness.

Key Findings

  • 24-Hour Urine N-Methylhistamine: 109 mcg/g Creatinine (Normal)
  • 24-Hour Creatinine: 1,276 mg/24 hr (Normal)
  • Urine Volume: 2,200 mL
  • Collection Duration: 24 hours
  • Overall Interpretation: No laboratory evidence of excessive mast cell activation.

Related Reports

  • July 26, 2022 – Serum Tryptase Evaluation
  • August 31, 2021 – Initial Systemic Inflammatory Evaluation
  • October 13, 2021 – Peak Systemic Inflammatory Evaluation
  • Autoimmune Evaluation
  • Allergy / Immunology Evaluation
  • Rheumatology Consultation Summary
  • Medical History Timeline

Navigation

  • Previous Report: July 26, 2022 – Serum Tryptase Evaluation
  • Next Report: Subsequent 2022 Laboratory Evaluation
  • Return to Laboratory Library
  • Return to Health Inventory

Observation

This report is especially meaningful when paired with Laboratory Report #23 (Serum Tryptase). Together, these two studies evaluate different aspects of mast cell biology:

  • Serum Tryptase assesses mast cell burden and recent degranulation.
  • 24-Hour Urine N-Methylhistamine assesses histamine metabolism over an entire day.

Both studies were normal, making a mast cell disorder an unlikely explanation for your symptoms. Viewed alongside the negative rheumatoid arthritis, lupus, Sjögren’s, infection, and muscle disease evaluations, these results illustrate how thorough your physicians were in investigating potential causes of your 2021 illness. This comprehensive diagnostic workup will become one of the strengths of your Health Inventory because it documents not only what was found, but also what was carefully ruled out.