51Cr Red Blood Cells in the Study of Hematologic Disease: A Historical Review

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FIGURE 1.
Decay scheme for ⁵¹Cr. EC = electron capture.
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FIGURE 2.
Composition of blood and components of blood volume. Hematocrit (arrow) is fractional relationship between plasma volume and red cell volume. (Reprinted from (23).)

TABLE 1.

Requirements of Radiolabeled Red Blood Cells for In Vivo Studies

Requirement no.	Description
1	Procedure, chemicals, and radionuclide are nontoxic to cell
2	Labeling is independent of age of cell (nonspecific)
3	Cellular labeling is firm, with no elution
4	Cells are not reutilized

TABLE 2.

Radiolabeling of Red Blood Cells with ⁵¹Cr Using Citrate Washing Procedure

Step	Procedure
1	10 mL of blood are placed in sterile, empty 25-mL vial
2	2 mL of acid-citrate-dextrose anticoagulant are added and swirled gently to mix
3	5 mL of citrate-phosphate buffer (pH 6.4–6.9) are added and swirled gently to mix
4	Cell suspension is centrifuged gently, and supernatant is removed/discarded
5	Washed cells are resuspended using normal saline solution
6	0.925 MBq (25 μCi) of ⁵¹Cr sodium chromate is added and swirled gently to mix
7	Incubation is performed at room temperature with occasional mixing for 20 min
8	Cell suspension is centrifuged gently, and supernatant is removed/discarded
9	⁵¹Cr-labeled cells are resuspended using normal saline solution

TABLE 3.

International Committee for Standardization in Haematology ⁵¹Cr Radiolabeling of Red Blood Cells

Step	Procedure
1	Whole blood (10 volumes) is added to NIH ACD-A solution (1–5 volumes)
2	Cell suspension is centrifuged gently (∼1,000 g) for 5 min
3	Supernatant is removed and discarded
4	⁵¹Cr sodium chromate (7.4 kBq/kg of body weight) in volume ≥ 0.2 mL is added and mixed gently
5	Incubation is performed for 15 min at 37°C
6	⁵¹Cr-labeled cells are washed twice in 4–5 volumes of isotonic saline
7	Cells are resuspended in volume of isotonic saline to provide infusion volume of 10 mL

TABLE 4.

Sodium Chromate ⁵¹Cr Injection USP Prescribing Information Radiolabeling Procedure

Step	Procedure
1	Whole blood (30–50 mL) is added to sterile vial containing ACD solution (5–10 mL) with gentle mixing
2	1.85–7.4 MBq (50–200 μCi) of ⁵¹Cr sodium chromate are added to vial, and whole-blood suspension is incubated at room temperature with frequent gentle mixing (swirling)
3	Red blood cell labeling is terminated with addition of 50–100 mg of ascorbic acid for injection USP
4	⁵¹Cr whole blood is centrifuged, and supernatant (plasma) radioactivity is removed
5	⁵¹Cr red blood cells are resuspended in normal saline solution USP to known volume
6	Red blood cells are assayed in dose calibrator and reinjected into patient