Erythrocyte Protoporphyrin, Free

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Erythrocyte Protoporphyrin, Free

Synonym/acronym: Free erythrocyte protoporphyrin (FEP).

Common use

To assist in diagnosing anemias related to chronic disease, hemolysis, iron deficiency, and lead toxicity.


Whole blood (1 mL) collected in a lavender-top (EDTA), royal blue-top (EDTA), or a pink-top (EDTA) tube.

Normal findings

(Method: Fluorometry)
Conventional UnitsSI Units (Conventional Units × 0.0178)
Less than 30 mcg/dLLess than 0.534 micromol/L
Less than 40 mcg/dLLess than 0.712 micromol/L


The free erythrocyte protoporphyrin (FEP) test measures the concentration of nonheme protoporphyrin in red blood cells. Protoporphyrin comprises the predominant porphyrin in red blood cells, which combines with iron to form the heme portion of hemoglobin. Protoporphyrin converts to bilirubin, combines with albumin, and remains unconjugated in the circulation after hemoglobin breakdown. Increased amounts of protoporphyrin can be detected in erythrocytes, urine, and stool in conditions interfering with heme synthesis. Protoporphyria is an autosomal dominant disorder in which increased amounts of protoporphyrin are secreted and excreted; the disorder is thought to be the result of an enzyme deficiency. Protoporphyria causes photosensitivity and may lead to cirrhosis of the liver and cholelithiasis as a result of protoporphyrin deposits. FEP is elevated in cases of lead toxicity or chronic exposure.

This procedure is contraindicated for



  • Assist in the diagnosis of erythropoietic protoporphyrias
  • Assist in the differential diagnosis of iron deficiency in pediatric patients
  • Evaluate lead poisoning

Potential diagnosis

Increased in

  • Anemia of chronic disease (related to accumulation of protoporphyrin in the absence of available iron)
  • Conditions with marked erythropoiesis (e.g., hemolytic anemias) (related to increased cell destruction)
  • Erythropoietic protoporphyria (related to abnormal increased secretion)
  • Iron-deficiency anemias (related to accumulation of protoporphyrin in the absence of available iron)
  • Lead poisoning (possibly related to inactivation of enzymes involved in iron binding or transfer)
  • Some sideroblastic anemias

Decreased in


Critical findings


Interfering factors

  • Drugs that may increase FEP levels include erythropoietin.
  • The test is unreliable in infants less than 6 mo of age.

Nursing Implications and Procedure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in diagnosing specific types of anemias and lead toxicity as well as monitor chronic lead exposure.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s hematopoietic system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues,  as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture. Specimens should be protected from light.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Provide contact information, if desired, for the American Porphyria Foundation (
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include CBC hematocrit, CBC hemoglobin, iron/TIBC, lead, and urine porphyrins.
  • Refer to the Hematopoietic System table at the end of the book for related tests by body system.
References in periodicals archive ?
Free erythrocyte protoporphyrin assay in the diagnosis of iron deficiency in the anemic aged subject.
The definition of iron deficiency was an abnormal value for at least two of the following three indicators: serum ferritin, transferrin saturation, and free erythrocyte protoporphyrin. Persons with iron deficiency and a low hemoglobin value were considered to have iron deficiency anemia (4).
Iron deficiency has three stages: iron depletion (low ferritin); decreased iron transport (low transferrin saturation); and diminished production of hemoglobin (increased free erythrocyte protoporphyrin, anemia, and microcytosis).[8] Psychomotor deficits have been linked to the final stage of iron deficiency, ie, severe iron deficiency or IDA.[2,3] Therefore, to prevent these deficits, it is necessary to identify iron-deficient infants before they develop anemia.
A comparison between concentrations of free erythrocyte protoporphyrin and serum ferritin during development of iron deficiency by phlebotomy in polycythaemia vera patients.
During routine screening, the patient's blood lead and free erythrocyte protoporphyrin (FEP) levels were found to be elevated (2.00 [mu]mol/L [41 [mu]g/dL] and 2.04 [mu]mol/L [115 [mu]g/dL], respectively).
Free erythrocyte protoporphyrin, zinc protoporphyrin and blood lead in newly re-exposed smelter workers: a prospective study.