Fundamentals of Fluorescein Angiography
Characteristics of Fluorescein

Timothy J. Bennett, CRA FOPS
Department of Ophthalmology
Penn State University
Hershey, Pennsylvania

Fluorescein Sodium

Fluorescein sodium is a highly fluorescent chemical compound synthesized from the petroleum derivatives resorcinol and phthalic anhydride.(1) It absorbs blue light, with peak absorption and excitation occurring at wavelengths between 465-490nm. Fluorescence occurs at the yellow-green wavelengths of 520 to 530nm. These fluorescent properties have made fluorescein useful in a variety of industrial, scientific and medical applications since the dye was first synthesized by Von Baeyer in 1871. Although commonly referred to as fluorescein, the dye used in angiography is fluorescein sodium, the sodium salt of fluorescein. Another common misconception, often passed on to patients, is that it is a 'vegetable dye' rather than a synthetic.

Excitation and Emission Curves of Fluorescein Sodium

The normal adult dosage is 500mg injected intravenously. It is typically packaged in doses of 5 ml. of 10% or 2 ml. of 25%. Upon entering the circulation, approximately 80% of the dye molecules bind to serum protein. The remaining unbound or free fluorescein molecules fluoresce when excited with light of the appropriate wavelength. The dye is metabolized by the kidneys and is eliminated through the urine within 24 to 36 hours of administration. During this period of metabolism and elimination, fluorescein has the potential to interfere with clinical laboratory tests that use fluorescence as a diagnostic marker.(2) To avoid false readings, clinical lab tests should be performed either before the angiogram, or postponed for a day or two to allow sufficient elimination of the fluorescein dye. Side effects of intravenous fluorescein include discoloration of the urine for 24 to 36 hours and a slight yellow skin discoloration that fades within a few hours. Nursing mothers should be cautioned that fluorescein is also excreted in human milk.(3)

Complications and Adverse Reactions

Fluorescein is well tolerated by most patients, but angiography is an invasive procedure with an associated risk of complication or adverse reaction. Adverse reactions occur in 5 to 10 percent of patients and can range from mild to severe. Transient nausea and occasional vomiting are the most common reactions and require no treatment. These mild reactions seem to be related to the volume of dye and rate of injection. A relatively slow rate of injection often reduces or eliminates this type of reaction. More severe reactions are rare, but include hives, laryngeal edema, bronchospasm, syncope, anaphylaxis, myocardial infarction and cardiac arrest.(4)

Although there are no known risks or adverse reactions associated with pregnancy, most practitioners will avoid performing fluorescein angiography in pregnant women, especially in their first trimester.(5-7)

Extravasation of fluorescein dye during the injection can be a serious complication of angiography. With a pH of 8 to 9.8, fluorescein infiltration can be quite painful. Sloughing of the skin, localized necrosis, subcutaneous granuloma, and toxic neuritis have been reported following extravasation of fluorescein. With proper injection technique, these complications can usually be avoided. Although life-threatening reactions during angiography are rare, the angiographic facility should be properly equipped and prepared to manage serious reactions to the procedure. It is generally recommended that a physician be present or available during angiography.