| Specimen requirement |
Spot urine: Plain urine bottle Volume: 10 mL |
| Authorisation code required | No |
| 24 Hr available service | No |
| Precaution |
Avoid using morning or evening urine or samples obtained after excessive fluid intake by patients.
Urine collected in a light-shield container and delivered to the laboratory without delay. |
| Method | Solvent extraction and check for fluorescence under ultraviolet light. |
| Reference interval | Normal: negative |
| Clinical indication | Diagnosis of acute neurological porphyrias (acute intermittent porphyria, porphyria variegata, hereditary coproporphyria) or porphyria cutanea tarda. The test is only reliable if the patient is symptomatic when the specimen is collected. It may be used to diagnose lead poisoning but blood lead is the recommended test. |
| Result interpretation |
A negative screening test is usually reliable to rule out the diagnosis in a symptomatic patient. In the latent phase of porphyria, screening tests are too insensitive to diagnose acute intermittent porphyria. Properly performed, negative tests for faecal porphyrins almost certainly exclude the diagnosis of porphyria variegate. Tests are negative before puberty even in children who are suffering from porphyria. Positive results must be confirmed by quantitative analysis and by typing the porphyrins. (See urine ALA / PBG.) There are causes other than porphyria for increased porphyrin excretion. |
| Measurement of uncertainty | See table. |
| Frequency of measurement | Daily |