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Introduction ⬇

Normally, there is a small amount of excess porphyrin at the completion of heme synthesis. This excess is cell free erythrocyte protoporphyrin (FEP). The amount of FEP in the erythrocyte is elevated when the iron supply is diminished.

This test is useful in screening for RBC disorders such as iron deficiency and lead exposure, especially in children 6 months to 5 years of age. This is the test of choice to diagnose erythropoietic protoporphyria. This test should not be used for screening for lead poisoning in children.

Normal Findings ⬆ ⬇

Men: <30 μg/dL of packed RBCs

Women: <40 μg/dL of packed RBCs

Clinical Alert

Critical ValueFEP >30 g/dL or >300 g/L

Procedure ⬆ ⬇

  1. Obtain a 5-mL sample of anticoagulated (EDTA or heparin may be used) venous blood. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

  2. Protect the blood sample from light.

  3. Wash the cells and then test for porphyrins.

  4. Be aware that the Hct must be known for test interpretation.

Clinical Implications ⬆ ⬇

  1. Increased FEP is associated with:

    1. Iron-deficiency anemias (elevated before anemia)

    2. Lead poisoning (chronic)

    3. Halogenated solvents and many drugs (see Appendix E)

    4. Anemia of chronic disease

    5. Acquired idiopathic sideroblastic anemia (most cases)

    6. Erythropoietic protoporphyria

  2. FEP is normal in:

    1. Thalassemia minor (and therefore can be used to differentiate this from iron deficiency and other disorders of globin synthesis)

    2. Pyridoxine-responsive anemia

    3. Certain forms of sideroblastic anemia due to proximal block to protoporphyrin

Interventions ⬆

Pretest Patient Care

  1. Explain test purpose and sampling procedure.

  2. Note on laboratory slip or computer any medications the patient is taking that cause intermittent porphyria. Discontinue such medications before testing (after checking with the healthcare provider).

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

Posttest Patient Care

  1. Have the patient resume normal activities and diet.

  2. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Monitor for porphyria or lead poisoning.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.