125I-Labeled Fibrinogen (Fibrinogen Uptake) Leg Scan

Norm of 125I-Labeled Fibrinogen (Fibrinogen Uptake) Leg Scan

No evidence of thrombi. No areas of abnormal concentration in the deep veins of the lower legs.


Usage of 125I-Labeled Fibrinogen (Fibrinogen Uptake) Leg Scan

Used to monitor the development and progression of deep vein thromboses. Longitudinal screening for clients at risk for thrombotic processes.
Positive of 125I-Labeled Fibrinogen (Fibrinogen Uptake) Leg Scan
Deep vein thrombosis, thrombophlebitis, and thrombosis.
Negative of 125I-Labeled Fibrinogen (Fibrinogen Uptake) Leg Scan
Normal finding. Also negative after the active clotting process has stopped.


Description of 125I-Labeled Fibrinogen (Fibrinogen Uptake) Leg Scan

Fibrinogen (factor I) is a complex polypeptide that converts to the insoluble polymer of fibrin after thrombin enzymatic action and combines with platelets to clot the blood. The 125I-labeled fibrinogen leg scan is an invasive, nuclear medicine test involving the intravenous injection of radionuclide-labeled fibrinogen (fibrinogen labeled with radioactive iodine) and scanning with a well counter for subsequent incorporation of the radioactive material into a thrombus. The scan measures increased surface radioactivity (>20%), which indicates uptake by thrombi in the leg(s). The test is most useful in detecting actively forming thromboses of the calf; 85% of positive results are seen within the first 24 hours after the calf is injected with iodine-125.


Professional Considerations of 125I-Labeled Fibrinogen (Fibrinogen Uptake) Leg Scan

Consent form IS required.

Infection, allergic reaction to radiolabeled fibrinogen (itching, hives, rash, tight feeling in the throat, shortness of breath, bronchospasm, anaphylaxis, death).
Anticoagulant therapy, bleeding disorders, thrombocytopenia, during pregnancy or breast-feeding, previous allergy to radiolabeled albumin.



  1. Ten drops of Lugol's solution in juice are given to block thyroid gland uptake of the radioactive tracer.
  2. Establish 18-gauge intravenous access.
  3. Have emergency equipment readily available.
  4. Assess for swelling in the calf, tenderness, and cyanosis of the skin.
  5. Assess for Homans' sign. Once it is determined to be positive, do NOT repeat Homans' sign assessment.
  6. Elevate the legs during the imaging procedure, which takes about 10 minutes.
  7. Just before beginning the procedure, take a “time out” to verify the correct client, procedure, and site.



  1. The client's legs are elevated during scanning to prevent pooling of blood in the veins of the legs.
  2. 125I-labeled fibrinogen is injected intravenously, and serial scans are performed on each leg 1, 4, 24, and 48 hours afterward. Surface radioactivity may be measured daily for as long as 2 days.
  3. The extremity is marked in segments along the course of the vein tract.
  4. Areas of fibrinogen incorporation into a thrombus are detected with the counter as areas exhibiting increased radioactivity, indicating increased concentration of radioactive tracer.


Postprocedure Care

  1. Maintain bed rest if thrombi are detected.
  2. Do not wash off markings on the extremity.
  3. Assess the venipuncture site for infiltration.
  4. Assess for swelling in the calf, tenderness, and cyanosis of the skin.
  5. Observe the client carefully for up to 60 minutes after the study for a possible (anaphylactic) reaction to the radionuclide.
  6. For 24 hours after the procedure, wear rubber gloves when discarding urine. Wash the gloved hands with soap and water before removing the gloves. Wash the ungloved hands after the gloves have been removed.


Client and Family Teaching

  1. This test involves several leg scans after the client receives an intravenous tracer that shows up on the scan. Scanning may continue for up to 2 days after the injection.
  2. The test poses no risk of radioactive damage to the client.
  3. Maintain bed rest until deep venous thrombosis (DVT) has been ruled out.
  4. Meticulously wash hands with soap and water after each void for 24 hours.


Factors That Affect Results

  1. False-negative results may occur where active clot formation is completed, but the thrombus still remains.
  2. Usually 1–2 days are required for enough radiolabeled fibrinogen to be incorporated into the clot before the clot can be detected.
  3. Thrombi of the pelvis are difficult to detect with this test.
  4. False-positive results may occur in clients with bacterial inflammatory conditions of the lower extremities.
  5. A radioactive test within the previous 24 hours invalidates the results.
  6. Up to 72 hours may elapse before the results become positive.


Other Data

  1. Other tests to detect DVT are Doppler ultrasonography, venography, thermography, perfusion lung scan, gas ventilation lung scan, and pulmonary angiography.
  2. This test is insensitive to upper thigh and pelvic vein thrombosis.
  3. Rate of thrombosis is significantly less with laparoscopic intervention only.
  4. Health care professionals working in a nuclear medicine area must follow federal standards set by the Nuclear Regulatory Commission. These standards include precautions for handling the radioactive material and monitoring of potential radiation exposure.
  5. Iodine-125 half-life is 60 days.