False elevations in urinary metanephrines: under-recognised pitfall with 24-hour urinary volume collection

Area of Science:

• Clinical Chemistry
• Endocrinology
• Laboratory Medicine

Background:

• 24-hour urine collections are crucial for diagnosing conditions like pheochromocytoma.
• Accurate measurement of total urine volume is essential for correct interpretation of analyte concentrations.
• Laboratory data entry errors can significantly impact patient diagnosis and management.

Observation:

• A patient presented with an elevated 24-hour urine metanephrine screen during secondary hypertension workup.
• The reference laboratory incorrectly recorded the urine volume as 9750 mL instead of the actual 975 mL.
• This tenfold error in volume inputuation skewed the initial metanephrine results.

Findings:

• Upon correction of the inputted urine volume, the 24-hour urinary metanephrine levels were recalculated.
• The recalculated metanephrine levels fell within the normal range.
• The initial abnormal screening result was attributed to a laboratory data entry error, not a pathological condition.

Implications:

• This case underscores the potential for significant diagnostic errors due to incorrect urinary volume input in 24-hour collections.
• It highlights the importance of meticulous quality control in laboratory data handling.
• Clinicians should be aware of this specific type of laboratory error when interpreting 24-hour urine test results, particularly for conditions like pheochromocytoma.