ince the first report of technetium-99m (@mTc)la
beling ofred blood cells (RBC) in 1967 (1), the labeling
methods have been improved constantly to reduce the
cell damage, to increase the labeling efficiency and yield,
and to simplify the previous time-consuming proce
dures(2—9).
In the present study we combined the use of very
small tin amounts with the new approach described by
Srivastava and Chervu (10) avoiding centrifugation of
cells. The importance of each step was evaluated to
optimize this new labeling procedure.
METhODS
The labeling procedure of the initial experiments was as
follows. Heparinized whole blood was transferred to a vial,
and the stannous kit (see “Titrationof Tin Concentration―)
dissolved in saline was added anaerobically. Incubation was
allowed for 2 mm. The vial was then centrifugated upside
down and 0.5 ml ofpacked RBC was transferred to the [@mTc]
saline. After 15 mm incubation the labeling efficiency was
determined. The procedure of the following experiments is
described here. One milliliter of heparinized whole blood was
added to a kit containing 2.0 @gtin (total), 3.7 mg sodium
ReceivedFeb. 25, 1986;revision accepted May 27, 1986.
For reprints contact: Henning Kelbaek, MD, Dept. Clin Phys
iol/Nucl Med. Herlev Hospital, University of Copenhagen, DK
2730 Herlev, Denmark.
citrate, 5.5 mg dextrose, and 0.11 mg sodium chloride.*
Centrifugation of cells was avoided—instead, sodium hypo
chlorite (NaOC1) was added to oxidize the extracellular tin
before 99mTcincubation.
Titration of Tin Concentration
To determine the most appropriate amount of tin for
preparation of RBC prior to labeling. two different stannous
kits were investigated. Medronate IVcontaining stannous flu
oride, and Tecephos containing stannous pyrophosphate.
Initially, the stannous agents were added to 4—7ml of hepa
rinized whole blood in both healthy volunteers (n = 6) and
patients with heart diseases of various origin and medication
(n = 6) to give tin concentrations ofO, 0.5, 1, 2, 5, and 10 ig/
ml in the cell preparation. In addition, we performed tin
titrations with the two kits in the interval between 0 and 1 @ig/
ml to detect a possible lower border of the tin amount neces
sary to obtain high labeling yields. The following experiments
were carried out with blood from healthy volunteers (labora
tory staff).
Titration of NaOCl
In a series of sixexperiments(each experimentcomprising
four samples) 1 ml of blood was added to the 2-pg stannous
kit. After 5 mm oftin incubation, 0.1% NaOCI was added to
the blood in volumes ofO, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 2, 3, or 5
ml. Then, 0.3-0.5 ml 4.4% EDTA was added, and finally
[99mTc]@inewas added in doses of 5-10 mCi. Labeling effi
cienciesweredeterminedas cell bound activity/totalactivity
after 15mm incubationat 20°C.
The Journal of Nuclear Medicine
1770 Kelbaak
Technetium-99m Labeling of Red Blood Cells:
In Vitro Evaluation of a New Approach
Henning Kelbaek
Department ofClinical Physiology and Nuclear Medicine, Herlev Hospital,
University ofCopenhagen, Denmark
By titrationof two different stannous kits for @‘Tclabelingof red blood cells (ABC)we found
concentrations of 1—2 @gtin per ml of blood to give the highest labeling yield. Using a new kit
containing 2 @gof tin and 0.1% hypochlorite (NaOCI) as an oxidizing agent we labeled ABC
with @“Tcavoiding centrifugation of cells. To evaluate this new procedure we assessed the
dependency of tin incubation time, and addition of 4.4% EDTA as a chelating agent on
labelingefficiency.We also measured the dependency of EDTAon the stabilityof the label.
Optimalconditions for labeling of 1 ml of whole blood using the new stannous kit were: 5-10
mmof tin incubation, 0.2 ml of 0.1% hypochlorite, and 15 mm of @“Tcincubation.This
procedure resulted in a labeling efficiency of at least 96%. The overall effect of EDTA was not
an increased labelingefficiency,and EDTAincreased the stabilityof the labelwith only a few
percent. The promising results of this n@wlabeling approach encourage to further laboratory
investigations and eventual clinical evaluation of the procedure.
J Nucl Med 27:1770—1773,1986
