Urine & CSF

5-HIAA (24-h urine) unit converter

Serotonin breakdown product; screens for carcinoid tumors

Also known as: 5-Hydroxyindoleacetic acid

Converter

Enter a value in any unit and all other units fill in.

mg/24 h µmol/24 h

Worked example

7.45 mg/24 h (middle of the reference range) = 39 µmol/24 h

Conversion formulas

µmol/24 h	µmol/24 h = mg/24 h × 5.231	mg/24 h = µmol/24 h × 0.1912

Reference range

Unit	Adults
mg/24 h	0 – 14.9
µmol/24 h	0 – 77.94

Source: LabCorp: 5-Hydroxyindoleacetic Acid (HIAA), Quantitative, 24-Hour Urine · Last reviewed: 2026-10-14

Note from the source: Carcinoid-tumor screening; serotonin-rich foods (bananas, tomatoes, walnuts, avocados) and some drugs cause false elevation

Frequently asked questions

How do I convert 5-HIAA (24-h urine) from mg/24 h to µmol/24 h?

µmol/24 h = mg/24 h × 5.231. In the other direction: mg/24 h = µmol/24 h × 0.1912.

What is the reference range of 5-HIAA (24-h urine)?

For adults the range is 0 – 14.9 mg/24 h (LabCorp: 5-Hydroxyindoleacetic Acid (HIAA), Quantitative, 24-Hour Urine). Reference ranges differ between laboratories and partly by sex and age; use the range printed on your lab report.

Which units are used for 5-HIAA (24-h urine)?

Common units are mg/24 h, µmol/24 h.