Journal of Radioanalytical and Nuclear Chonistry, Articles, Vol. 124, No. 1 (1988) 85-95

IN VIVO MONITORING O 7 SKELETAL ALUMINUM B UR DE N IN PATIENTS WITH R E N A L F A I L U R E

K. J. ELLIS,* S. KELLEHER,** A. RACITI,** J. SAVORY,*** M. WILLS***

*Medical Department, Brookhaven National Laboratory, Upton, New York 119 73 ( USA )

**Health Science Center, SUNY~tony Brook, Stony Brook, New York 11794 (USA)

***University of Virginia Medical School, Charlottesville, Virginia 22908 (USA)

(Received February 8, 1988)

In vivo neutron activation analysis was used to examine the total body and partial body (hand) aluminum levels in patients with end-stage renal failure. Patients maintained on chronic hemodialysis had higher mean body burdens of aluminum than did those clinically managed without dialysis. Approximately 70% of the patients examined indicated elevated levels of body or skeletal aluminum. A significant correlation was observed between the in rive aluminum/calcium ratio obtained for the hand measurement and the increase in serum aluminum levels following a disferroxamine infusion test. The direct in vivo monitoring of hand A1/Ca values inpatients may provide an alternate choice to bone biopsy for the detection of aluminum intoxication.

I n . e d u c t i o n

The a c c u m u l a t i o n o f a luminum, i n p a t i e n t s w i t h c h r o n i c r e n a l f a i l u r e h a s

b e e n a t t r i b u t e d to t h e u s e o f a l u m i n u m - b a s e d p h o s p h a t e b i n d e r s and t o t r a c e

c o n t a m i n a t i o n o f d i a l y s a t e w a t e r . 1 -5 E p i d e m i o l o g i c a l s t u d i e s o f p a t i e n t s

on hemodlalysls have identified aluminum as a co-factor for the development

of dementia and osteomalacic osteodystrophy.4,5 A major clinical problem

is the early detection of alumlnum-overload, particularly in the asymptoma=

tic patient. Serum aluminum concentrations are often increased in these

patients, but it Is still unknown if serum levels can provide a sufficient

discriminatory marker before a toxic response is evident. Bone biopsies

usually offer the final diagnosis, however, this procedure is not recom-

mended for routine monitoring of patlents. 6 The desferrloxamlne infusion

test is presently the most frequently used technique for assessing aluml-

Elsevi~Sequo~ A.,Lausanne Akacl~mi~Kiad6, Bud~p~t

K.J. ELLISetM.:IN VIVO MONITORING OF SKELETAL ALUMINUM

hum-over load i n p a t l e n t s . 7 This p rocedu re i s a l s o n o t w i t h o u t p o s s i b l e

adverse effects. The need, therefore, for a nou-invasive method suitable

for monitoring skeletal aluminum burdens in patients with chronic renal i

failure has prompted us to explore the development of in vlvo neutron acti-

vation techniques.

Methods

~otal Body Neutron Activation Analysis

The technique of total body neutron activation analysis (TBNAA) has

been d e s c r i b e d i n d e t a i l e l s e w h e r e , and only the main p o i n t s w i l l be p r e -

s e n t e d here.8, 9 The patient is irradiated with moderated fast neutrons

from fourteen 50 Ci 238pu,Be sources while in a supine position. Following

the 5 mln exposure (dose < 270 mrem), the subject is transferred (3 mln

delay) to the Brookhaven 5C-detector whole body counter and the induces

activity is counted for 15 min. This technique has been callbrated for the

measurement of whole body calcium s phosphorus, sodium, and chlorine.

Whereas body phosphorus is activated by the fast neutron reaction

31p(n,u)28AI, body aluminum is activated by the thermal neutron reaction

27Al(n,~)28Al. The induced radioactivity, 28Al, is the same for both reac-

tions, thus, it is not possible to unlquoly identify which reaction occurs

for a multl-energy neutron exposure.

Measurements using an anthropomorphic phantom containing solutions of

aluminum and phosphorus separately were performed. The Brookhaven TBNAA

technique showed that I g aluminum gave the same response as 68.3 g phos-

phorus. For ICRP standard reference man, I0 the estimated body content of

aluminum is small (0.06 g) when compared with the whole body phosphorus

value (~80 g). For 'standard man', the Brookhaven TBNAA measurement would

overestimate body phosphorus by 4 g due to the interference from body alu-

minum. In healthy subjects, it is reasonable to expect the body level of

86

K.J. ELLISetal.:INVIVO MONITORING OF SKELETAL ALUMINUM

aluminum to r ema in s m a l l , t h u s i n t r o d u c i n g l e s s t ha n 1Z e r r o r i n t h e meas-

u r em en t o f body p h o s p h o r u s . F u r t h e r m o r e , t he r a t i o o f t o t a l body phospho-

r u s (TBP) tO total body calcium (TBCa) is relatively constant in this popu-

lation. II Therefore, an elevated body aluminum level would appear as an

apparant increase in the TBP/TBCa ratio in excess of the expected value

based on the subjects' total body calcium measurement. That is, if

< TBP/TBCa > = constant = k

for the general population, then excess total body aluminum can be estl-

mated as

TBA1 = (TBP - k x TBCa)/68.3 (Eq. i)

For the general adult population (age range 20-80 years) measured by TBNAA

at Brookhaven, the following values of k were obtained: 0.442 ~ 13Z (cv)

for 178 males and 0.473 + 13Z (cv) for 435 females.

Partial Body Neutron Activation Analysls

In order to activate aluminum with mlninum interference from phospho-

rus, the thermal/eplthermal beam of the Brookhaven Medical Research Reactor

was used. The neutron energy distribution and flux characteristics of this

beam are well known and have been presented elsewhere. 12 A polyethylene

shleld/colllmator (60 cm x 60 cm x 60 cm) doped with boron and lead was

placed in front of the reactor beam port (Fig. 1). The beam area was

res~rlcted to approximately i0 cm x 20 cm for activation of the patient's

hand. The colllmator/shleld was also designed to protect the patient's

body. For a two-mlnute exposure of the hand (0.02 Sv) at 1 kwatt power

(1.3 x I07 n cm'2sec-l), the total body dose is less than 0.0003 Sv.

Variations in the thermal flux were measured in an anthromorphlc hand

phantom using gold foils. The thermal flux varied by ~IX at the figures,

+4Z in the palm region and +13Z at the wrist. There was also a mean reduc-

87

K. J. ELLIS et al.: IN VWO MONITORING OF SKELETAL ALUMINUM

t COOLED CORE

HAt

[~]] POLYETHYLENE CONCRETE BISMUTH GRAPHITE

I~ LEAD I~ DzO I~ STEEL

POLYETHYLENE (Pb, B doped)

Fig. 1. Hand collimator/body shield used at Medical Research Reactor for in vivo aluminum measurements

tion of the thermal flux by approximately 25% in the wrist region when com-

pared with the finger region.

Following the two-mlnute hand irradiation at the reactor, the patient

was transferred to the counting facility (delay time 2 mln). The induced

activity in the hand was counted for 200 sec using four Nal detectors

(4"x4"x16") arranged in a quasl-4~ geometry (Fig. 2). Normal hand movement

during counting introduced less than +2% error in the measurement of alumi-

num and calcium. A typical patient spectra is shown in Fig. 3. The detec-

tion limlt (~2 o) for aluminum was 0.4 mg in a hand phantom containing a

"standard man" solution of calcium, sodium and chlorine. The sensitivity

for aluminum was 400 counts per mg. Bone phosphorus produced minlnum

interference when activated and was equivalent to 4 ~g of aluminum per gm

of bone. Comparison between patients for absolute levels of aluminum and

88

K. J. ELLIS et al.: IN VIVO MONITORING OF SKELETAL ALUMINUM

, ; J .

c 16"

/ COUNTING CHAMBER

/ ~.'

Pb SHIELDING 4"x4"x16" No l (TI) DETECTOR o rt Fig. 2. Partial body counting system for hand activation measurements. Four 4 X 4" X 16 NaI detectors surround

the hand in a quasi-41r geometry

0 0 v

Z

o

900

500

IOC

I N a

1240

I I I

HAND ACTIVATION SPECTRA (Potient # 9 ) -

1880 2520 3160

ENERGY (keV)

Fig. 3. Typical spectra for the in vivo neutron activation of the human hand using the MediCal Research Reactor beam

calcium is difficult because of the variations in activation due to differ-

ences in hand geometries. 13 Therefore, the calcium photopeak was used as

an internal normalization standard for each patient as it reflected the

irradiated bone mass. The AI/Ca ratio, therefore, provided an index of

elevated aluminum per unit bone mass.

If one assumes the bones of the hand are representative of the total

89

K.J. ELLISet~.:IN VIVO MONITORING OF SKELETAL ALUMINUM

skeleton, then one can obtain an estimate of the total skeletal burden of

aluminum. This estimate is obtained as follows:

Alskeleton = (Al/Ca)hand x (calcium)tote I body (Eq. 2)

Total body calcium is obtained by the total body neutron activation proce-

dure described in the previous section.

Results

Total body 'phosphorus' and calcium were measured in 185 patients with

renal disease. The relationship between TBP and TBCa for tlle male patients

and for a control population of 178 males is shown in Fig. 4. It is evi-

dent that many of the renal patients had apparent phosphorus levels far in

excess of that expected for their body calcium levels. Normally, 80% of

body phosphorus is in bone, the remaining 20% being in soft tissue. The

large increases in body 'phosphorus' observed in the renal patients, there-

fore, were not physiologically possible. Using Eq. I to convert this

excess 'phosphorus' signal to a body aluminum level, the results for the

renal patients are presented in Table i. Individual values of estimated

body aluminum varied from non-detectable levels to body burdens above 8 g.

The mean aluminum values for the renal patients not on dialysis were lower

than the mean values for the patients requiring regular maintenance

dialysis. The combined mean body burden value for the 185 renal patients

was 1.3 g aluminum.

A second group of ten patients volunteered for the partial body meas-

urement of hand aluminum. Each patient was screened and found to be clini-

cally asymptomatic of any aluminum-associated complications. Each patient

also had their total body 'phosphorus' and calcium levels measured by

TBNAA. In addition, two serum aluminum values were obtained. A baseline

90

K. J. ELLIS et al.: IN VIVO MONITORING OF SKELETAL ALUMINUM

A

E

tn :D 13:: 0 "1- 13_ q') 0 "I" 13- >- 0 0 m

J

O t...-

1 0 0 0

7 5 0 -

5 0 0 -

2 5 0 -

0 3 0 0

I ' I w I I

X X - - X

R

+ X X X

x X l o x R X O0 r 0 0

OR XX X O R O O O 0 x R x o O R O O O O O O R O O o

x x x x oo c o ORXOX o 0

R O XX ~ 0 0 0 0 0 O O00

OR OO ~ 1 ~ ) 0 R R O O OO OOOOR

R o O o o O O ~ O OR O

o C O N T R O L S " RENAL FAILURE- x HEMODIALYSIS

I i I i I J 6 0 0 9 0 0 1 2 0 0 1500

TOTAL BODY CALCIUM (g in )

Fig. 4. Relationship between total body "phosphorus" and total body calcium obtained by in vivo neutron activation analysis. The elevated "phosphorus" values are due to interference from body aluminum

t.d I - LL ,::[

=,=L

: ~ n , - t o w ~ L L . _ l t o

uJ to

uJ 0c

Z

500

500

I00

r I I I r I I

O

o o

o o o

i 1 i I i i

0 . 0 0 . 2 0 0 . 4 0 0 . 6 0 0 . 8 0

H A N D A L U M I N U M / C A L C I U M R A T I O ( m g / g )

Fig. 5. Relationship between the increase in serum aluminum following disferroxamine dnfusion and the aluminum/calcium ratio obtained by in vivo neutron activation Of the hand

91

K. J. ELLIS et al.: IN VIVO MONITORING OF SKELETAL ALUMINUM

Table 1 Mean estimated total body

aluminum levels for patients with endstage renal disease

Oroup No. Patients

Estimated Total Body

Aluminum* (g)

Mean + sem (range)

Renal Failure

Males 39

Females 40

Hemodialysis

Males 59

Females 47

0.63 + 0.24 (0-7 .0)

1.18 + 0.27 (0-7.4)

1.87 + 0.22 (0-8.3)

t.55 + 0.23 (0-5.6)

*TBAI = (TBP - k x TBCa)/68.3 where k = 0.442 for males and

0.473 for females.

serum value and the increase in serum aluminum following administration of

dlsferroxamine (DFX). The results of these procedures are presented in

Table 2 for the ten patients with end-stage renal disease. The baseline

serum aluminum levels for these patients were below i00 ~g/l, a concentra-

tion often associated with significant bone aluminum levels. 6 Serum alumi-

num levels following DFX administration showed increase from 32 ~g/l to 450

~g/l. There was not correlated to the baseline serum values. There was

also no correlation between baseline serum aluminum or elevated serum

aluminum and the estimated total body aluminum value. Furthermore, there

waS no statistical evidence of a correlation between the total body

aluminum burden and either skeletal aluminum or the AI/Ca ratio for the

hand. A significant correlation (Fig. 5)~ however, was found between the

92

K. J. ELLIS et al.: IN VIVO MONITORING OF sKELETAL ALUMINUM

Table 2 Serum, hand, skeleton and total body

aluminum levels in ten patients with renal failure

Baseline Increased Hand Total Body Skeletal

Subject Serum AI Serum AI AI/Ca AI AI Burden

No. (~g/l) (~g/l) (mg/g) (mg) (m~)

i 19 32 .06 764 58

2 20 90 .021 2 12

3 26 190 .41 2683 200

4 28 71 .041 2 48 .,

5 31 130 .13 858 168

6 35 32 .031 1283 36

7 38 41 .06 1272 67

8 59 157 .I0 r 2 89

9 84 376 .48 996 294

10 98 450 .76 1588 380

IAlumlnum/calcium ratio within the normal range.

2Estlmated total body aluminum level was less than 300 mg, the upper limit

of the normal range.

increased serum aluminum level after disferroxamine (~AI(DFX)) and the

hand AI/Ca ratio:

AAI(DFX) ffi 0.547 x AI/Ca + 43 (Eq. 3)

where AAI and AI/Ca are in ~g/l and ~g/g units, respectively (r = .96,

p<.0Ol).

The three patients wi~h hand AI/Ca ratios within the normal range had

received clinical treatment for less than two years. The three patients

93

K.J. ELLISetfl . :INVIVO MONITORING OF SKELETAL ALUMINUM

wlth hand AI/Ca ratios above 0.30 had required maintenance dialysis for

more than 5 years. The total body aluminum values in the ten patients

ranged from non-detectable (<300 m E ) to above 2600 mg. Skeletal aluminum

burdens were estimated to range from 12 mg to 380 mg. The mean total body

and skeletal values for the ten patients were 1350 mg and 162 mE, respec-

�9 tively. These values represent approximately an 8-fold and 20-fold

increase when compared with 61 mg (total body) and 21 mg (skeleton) for

ICRP-23 reference man.

Discussion

The clinician needs an acceptable diagnostic technique that can easily

identify patients at increased risk of developing aluminum-induced bone

disease. When serum aluminum concentrations consistently exceed 100 pg/l,

then there is a virtual certainty (>98%) of having bone disease or develop-

ing it if the exposure continues. 14 This serum level, however, is not

routinely exceeded in most patients as was the case for our study of ten

patients. Other investigators, however, rely on serum aluminum only as a

monitor of recent aluminum loading in their patlents. 15 Our study more

closely supports this interpretation as the baseline serum aluminum levels

were not related to the estlmaCes of total body or skeletal aluminum. The

increase in serum aluminum following the dlsferroxamine infusion test,

however, was highly correlated with the hand AI/Ca ratio and skeletal

burden of alumlnQm. At present bone biopsy is the preferred choice for

detecting aluminum intoxication in patients with renal disease. We would

propose that the hand neutron activation technique provides an alternate

non-lnvaslve technique with sufficient sensitivity to detect elevated bone

aluminum levels in asymptomatlc patients wlth low serum aluminum values.

If patients are to be placed routinely on disferrioxamine therapy in order

94

. K.J. ELLISetfl.:IN VIVO MONITORING OF SKELETAL ALUMINUM

to reduce their body burden of aluminum, then there will be a need ~to study

the clinical course of bone aluminum levels. The hand activation procedure

provides an attractive alternative to the use of bone biopsies. A portable

system using a filtered beam from a 252Cf source is currently under

development for routine clinical screening.

Research supported under contract No. DE-ACO2-76CH00016 with the U.S. Department of Energy. We wish to thank Roman SHYPAILO for his assistance in the total body and hand activation procedures and Gloria JACKSON for preparation of the manuscript.

References

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Nephron, 34 (1983) 228. 14. R. J. WINNEY, J. F. COWlE, J. S. ROBSON, Clin. Nephrol., 24 (1985) $2. 15. P. GARRETT, Br. Med. J., 290 (1985) 1986.

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