Porphyrins are cyclic compounds formed from Δ-aminolevulinic acid (Δ-ALA), which plays a role in the formation of hemoglobin and other hemoproteins that function as carriers of oxygen in the blood and tissues. In healthy individuals, insignificant amounts of porphyrin are excreted in the urine. However, with certain conditions, such as porphyria (disturbance in metabolism of porphyrin), liver disease, and lead poisoning, increased levels of porphyrins and Δ-ALA are found in the urine. Disorders in porphyrin metabolism also result in increased amounts of porphobilinogen in urine. The most common signs and symptoms of acute intermittent porphyria are abdominal pain, photosensitivity, sensory neuropathy, or psychosis. Patients with the porphyrias may pass urine that is pink, port wine, or burgundy colored.

When urine is tested for the presence of porphyrins, porphobilinogen, or ALA, it is also given the black-light screening test (Wood light test). Porphyrins are fluorescent when exposed to black or ultraviolet light. See Chapter 2 for other tests for porphyria.

This test is used to diagnose porphyrias and lead poisoning in children. The following is a summary of laboratory findings for various porphyrias.

• Congenital erythropoietic porphyria. Elevations of urine uroporphyrin and coproporphyrin occur, with the former exceeding the latter. Lesser amounts of hepta-, hexa-, and pentacarboxyporphyrins are secreted. ALA and porphobilinogen levels are normal.

• Acute intermittent porphyria. Porphobilinogen and Δ-ALA are elevated in acute attacks, and small increases of urine uroporphyrin and coproporphyrin may be found. During periods of latency, the values are normal.

• Porphyria cutanea tarda. In this more common form of porphyria, increased uroporphyrins, uroporphyrinogen, and heptacarboxyporphyrins are seen.

• Protoporphyria. Mild disease, which mainly has the clinical symptoms of solar urticaria and solar eczema (from exposure to sunshine); increased fecal protoporphyrin.

• Hereditary coproporphyria. Urine coproporphyrin and porphobilinogen are markedly increased during acute attacks; increases of urine uroporphyrin may also be found.

• Variegate porphyria. In acute attacks, results are similar to those seen in acute intermittent porphyria. Porphobilinogen and Δ-ALA usually return to normal between attacks. Urine coproporphyrin exceeds uroporphyrin excretion during acute attacks.

• Chemical porphyrias (“intoxication porphyria”). Porphyrinogenic chemicals include certain halogenated hydrocarbons, which cause increased uroporphyrin levels in the urine. Also increased are ALA, coproporphyrin, and porphobilinogen.

• Lead poisoning.Δ-ALA levels exceed those of porphobilinogen, which may remain normal. In children, ALA secretion in urine is more sensitive than blood lead levels.

Porphyrins

Total and fractions: see Table 3.10

1. Properly label a 24-hour clean-catch urine container with the patient’s name, date and time of collection, and test(s) ordered.

2. Provide refrigeration or icing. The specimen must be kept protected from exposure to light. Check with your laboratory regarding the need for preservatives (e.g., 5 g of Na₂CO₃).

3. Follow general instructions for 24-hour urine collection (see Long-Term, Timed Urine Specimen [2-Hour, 24-Hour]).

4. Record exact starting and ending times on the specimen container and in the patient’s healthcare record.

5. Send the specimen to the laboratory.

6. Obtain midmorning or midafternoon specimens for random tests because it is more likely that the patient will excrete porphyrins at those times. Transport the specimen to the laboratory immediately. Protect the specimen from light.

7. Observe and record the urine color. If porphyrins are present, the urine may appear amber-red or burgundy in color, or it may vary from pale pink to almost black. Some patients excrete urine of normal color that turns dark after standing in the light.

1. Increased urine porphobilinogen occurs in:

   1. Porphyria (acute intermittent type)

   2. Variegate porphyria

   3. Hereditary coproporphyria

2. Increased fractionated porphyrins occur in:

   1. Acute intermittent porphyria

   2. Congenital erythropoietic porphyria

   3. Hereditary porphyria

   4. Variegate porphyria

   5. Chemical porphyria caused by heavy metal poisoning or carbon tetrachloride

   6. Lead poisoning

   7. Viral hepatitis

   8. Cirrhosis (alcoholism)

   9. Newborn of mother with porphyria

   10. Congenital hepatic porphyria

3. Increased urineΔ-ALA can occur in:

   1. Acute intermittent porphyria (acute phase)

   2. Variegate porphyria (during crisis)

   3. Hereditary coproporphyria

   4. Lead poisoning does not increase urine Δ-ALA until serum lead levels reach >40 μg/dL; urine Δ-ALA may remain elevated for several months after control of lead exposure.

   5. Congenital hepatic porphyria

   6. Slight increase in pregnancy, diabetic acidosis

4. Decreased urineΔ-ALA is found in alcoholic liver disease.

Pretest Patient Care

1. Explain purpose of test, procedure for 24-hour urine collection, and interfering factors. Written instructions can be helpful.

2. Allow food and fluids but advise the patient to avoid alcohol and excessive fluid intake during the 24-hour collection.

3. Obtain healthcare provider’s approval to discontinue all medications for 2–4 weeks before specimen collection, if possible, so that results will be accurate.

4. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. Oral contraceptives and diazepam can cause acute porphyria attacks in susceptible patients.

2. Alcohol ingestion interferes with the test.

3. Many other drugs, especially phenazopyridine, procaine, sulfamethoxazole, and the tetracyclines, interfere with the test (see Appendix E).