Type of test Urine (fresh and 24 hour)
Normal findings
Test explanation and related physiology
This test is a quantitative measurement of porphyrins and porphobilinogens. Along with measurement of aminolevulinic acid, the various forms of porphyria can be identified.
Porphyria is a group of genetic disorders associated with enzyme deficiencies involved with porphyrin synthesis or metabolism. Porphyrins (e.g., uroporphyrin and coproporphyrin) and porphobilinogens are important building blocks in the synthesis of heme. Heme is incorporated into hemoglobin in the erythroid cells. In most forms of porphyria, increased levels of porphyrins and porphobilinogens are found in the urine. Heavy metal (lead) intoxication is also associated with increased porphyrins in the urine.
Urine tests for porphyrins are not as accurate as plasma measurements and pattern identification for the various forms of porphyria. They are accurate, however, in screening for porphyria, especially the intermittent variety. Porphyrin fractionation of erythrocytes and plasma provides specific assays for primary RBC porphyrins. These assays are predominantly used to differentiate the various forms of congenital porphyrias. Plasma measurement of free erythrocyte protoporphyrin (FEP) is helpful in the diagnosis of iron-deficiency anemia or lead intoxication.
Interfering factors
* Drugs that may alter test results include aminosalicylic acid, barbiturates, chloral hydrate, chlorpropamide, ethyl alcohol, griseofulvin, morphine, oral contraceptives, phenazopyridine, procaine, and sulfonamides.
Procedure and patient care
• See inside front cover for Routine Urine Testing for random and 24-hour collection.
• Protect the specimen from light.
* Instruct the patient to avoid alcohol during the collection period.
• Keep the 24-hour urine in a light-resistant specimen bottle with a preservative to prevent degradation of the light- sensitive porphyrin.
* Encourage the patient to drink fluids during the 24 hours unless contraindicated for medical purposes.
Abnormal findings
Increased levels
- Porphyrias
- Liver disease
- Lead poisoning
- Pellagra
