(Revised April 3; revision accepted for publication August 10, 1969.)
E.P.L. is recipient of Postdoctoral Fellowship of the Schweizerischer Nationalfonds.
This investigation was supported in part by Training Grant No. HD-00182 from the Institute of
Child Health and Human Development, National Institutes of Health.
ADDRESS FOR REPRINTS: (M.H.) San Francisco General Hospital, Building 100, Room 246, 1001 Potrero Street, San Francisco, California 94110.
PEDIATRICS, Vol. 44, No. (3, I)ecembcr 1969 905
ARTICLES
SINGLE
INJECTION
CLEARANCE
IN
CHILDREN
Tadasu
Sakai, M.D.,Ernst
P.Leumann,
M.D., and Malcolm A. Holliday, M.D.From the Department of Pediatrics, University of California-San Francisco Medical Center, and San Francisco General Hospital, San Francisco
ABSTRACT. The renal clearance of sodium
iothalamate I’s’ after a single intravenous dose of 10 to 25 pCi was calculated from the plasma disappearance curve. The endogenous creatinine clearance was compared with these results.
Thirty-eight studies in 35 pediatric patients with all
levels of renal function were performed. Eight studies were excluded because of grossly incom-plete urine collection, and 5 studies were not analyzed further because of very low glomerular
filtration rate. The correlation between both
meth-ods in the 21 studies was good (Cereat = 0.91 X C. + 4.9, r = 0.91). It was significantly better in the nine patients with a serum creatinine of
0.7 mg/100 ml or more (Ccreat = 1.01 X C.1
-1.2, r = 0.97) than in the 16 patients with a
serum creatinine of 0.6 mg/100 ml or less (C
= 0.82
x
C + 11.5, r = 0.84). In the lattergroup, the accuracy of the serum creatinine (Ic-termination was often poor, and even variations of ± 0.1 mg/100 ml could lead to a gross error in the calculation of the clearance.
In four patients, the clearance was obtained by external counting and agreed well with the clearance calculated from the plasma samples.
The single injection clearance is especially in-dicated in children (1) when no adequate urine
collection is obtainable, (2) at low serum
creatin-me concentrations, and (3) in outpatients. Pedi-atrics, 44:905, 1969, KIDNEY FUNCTION TESTS,
GLOMERULAR FILTRATION RATE, DIAGNOSTIC IODINE
ISOTOPES, CREATININE.
rJ,
HE determination of glomerularfiltra-tion rate (GFR) is of major interest in
the evaluation of kidney function. Since
standard clearance techniques with
con-stant infusion and catheterization of the
bladder cannot be done routinely, the
de-termination of the endogenous urea or
crea-tinine clearance is used widely. In the
pedi-atric age group, the estimation of creatinine
clearance is less accurate than in adults,
frequently due to incomplete urine
collec-tions and also to difficulties in determining
the serum creatinine at low concentrations.
Methods by which GFR can be
esti-mated without any urine collection have
obvious advantages. One possibility consists
in calculating the clearance from the
plasma disappearance curve after the single
injection of a substance which is handled
like inulin. Several authors have proven
this method to correlate well with the
con-stant infusion inulin or endogenous
creati-nine clearance in animals” and humans3’4
using labelled substances and calculating
the data according to the model of
Sapir-stein,
et al.
Our study demonstrates thetechnical feasibility of the single injection
clearance with iothalamate J125 in chik1ren
and investigates the merits of this method
as an alternative to the creatinine
clear-ance.
MATERIAL AND METHODS
Thirty-eight single injection clearances
using sodium iothalamate J125 (C,1) were
performed on 35 pediatric patients with
various levels of renal function. None of
them was edematous at the time of study.
The creatinine clearance (Ccreat) was
mea-sured in the same children. After emptying
the bladder, a 24-hour (27 studies) or
12-hour (11 studies) urine was collected,
end-ing at 8 A.M., at which time a fasting blood
(
0.6931slopes: Xa =
T112,
using a modification of the method of Folin
and Wii.” The measured creatinine
excre-lion in 24 hours was then compared with
an expected value, which was calculated
from the regression equation reported by
Graystone : Great = 24.3 X (wt) - 150 for
boys ( over 5 years ) and Great = 20.9 X
(wt) - 75 in girls. In one young male
pa-tient (study No. 27), the equation for boys
under 18 months was used: Great 11.7
X (wt) - 4. It was assumed that a ratio
(measured creatinine excretion : expected
value) of 0.70 or less indicated a grossly
incomplete urine collection. Accordingly,
eight studies with ratios between 0.23 and
0.67 were excluded.
Commercial indicator substance sodium
iothalamate 1125 (Glofil, Abbott
Labora-tory), shown to have a clearance identical
with inulin,7’8 was used to estimate GFR.
The specific activity averaged 200 Gi/mg,
and its concentration 1.1 to 1.3 mg/mi. A
1:5 dilution of sodium iothalamate P25 in
saline (10 to 25 Gi in 0.5 mlf) was used.
Each patient was given 2 drops of Lugol’s
solution by mouth the night before the test,
but no special diet or water restriction was
instituted.
The dose of sodium iothalamate 1125
(10-25 p.Ci) was prepared in a disposable
1 ml plastic syringe and was injected rap-idly into the intravenous infusion tubing. In
a similar manner, approximately 0.5 ml of
the same sodium iothalamate J125 dilute
so-lution was diluted further to 100 ml and
used as a standard. The amount used for
the patient and for the standard was
deter-mined by weighing the syringe prior to and
following the injection. At regular short
in-tervals (usually 10, 20, 30, 80, 100, and 120
minutes after injection of sodium
iothala-mate 1125), a 3 ml blood sample was drawn
from an indwelling needle which had been
placed into the antecubital vein at the
be-ginning of the procedure.
oTechnicon Corporation, Tarrytown, New York. Five milliliters have been used since comple-tion of the study in order to minimize losses occur-ring at the time of injection.
milliliter of plasma and two 100 .tl
dupli-cate samples of the diluted aliquot were
pi-petted (micropipettes : ± 1% accuracy)
into counting tubes which contained 1 ml
water, and all were counted in a well-type
scintillation counter up to 10,000 counts.
The counts per minute (cpm) per milliliter
plasma and the total counts injected were
then derived. Plasma samples were
ob-tained before injection of the iothalamate in
those patients who had previously
under-gone a study with a labelled substance, but
the cpm were identical with water in all
in-stances.
The single injection clearance was
calcu-lated on the basis of the two-compartment
model proposed by Sapirstein, et al. The
plasma disappearance curve could be
re-solved graphically into two single
expo-nential functions represented by the two
slopes ?a and )b (Fig. 1) by fitting a
straight line to the terminal segment of the
curve.
(Xii: intercept with the Y axis =
A,
half-life time = T1120)
(Xb: intercept with the Y axis = B,
half-life time = Ti/Ib) 0.6931
Xb =
T1/2b
According to the mathematical treatment of
Sapirstein’s model, the clearance C can now
be calculated as follows:
IXaXb JO 6931
C=
AXb-I-B-Xa ATl/I,+BTl/,b
I total dose (in cpm) given to the
pa-tient. A desk model computer (Olivetti
Pro-gramma 101) was programmed to perform
calculations based on the foregoing
equa-tions.
In four patients the slope of
disappear-ance was monitored externally by affixing a
scintillation probe to the precordium and
recording directly from 0 to 30 minutes,
* Olivetti-Underwood Corporation, New York,
I I I I
= 455050 x 0.6931 = 75 mI/mm
100 - 105 x 7.4 + 50.9 x 67.3
-80A “
I
(j.) B=50.9
\
I’/2b67.3-IC) 10
\
Xb=O.O1O3VI - A105
0 4-. .
-If2
-= 0.0937
-2-
-I I I I I I I I
10 20 30 40 50 70 80 90 100 110 120
Fic. 1. Plasma disappearance rate of sodium iothalamate I’ after a single intravenous injection. The bi-exponential curve is resolved by eye-fit into the slopes X a and X b. A and B are the respective
intercepts at the Y axis. (Study No. 13) 60
ARTICLES
Time
(mm.)
907
and again from 80 to 120 minutes after
in-jection. The external counts were converted
to plasma radioactivity using plasma cpm
from a sample which was obtained at
ap-proximately 120 minutes after injection.
The calculation was by the following:
Body monitoring cpm at T1
-Plasma cpm at T1 (unknown)
Body monitoring cpm at T2
Plasma cpm at T2
The instrumental system utilized included a
2 X 2 in. sodium iodide crystal shielded
scintillation probe with a 2 in. straight bore
collimator, a Nuclear Chicago Analyzer
Model 1810 set for energy range 19 key to
50 key, and a Nuclear Chicago Ratemeter
Model 1620 B, and was recorded on a
Min-neapolis Honeywell Visicorderti Model
1108.
All data of the single injection clearance
were analyzed by computer and also
deter-mined by plotting the plasma radioactivity
against time on semilogarithmic paper and
resolving the disappearance by eye (Fig.
1). The three points defining each slope lay
generally on a straight line, except for the
first point (corresponding to the first blood
sample), which was higher than expected
in 11 of 29 instances. The uncertainty in
drawing the steep slope Xa) resulted,
how-ever, only in a small error, and the results
obtained by this method and by computer
agreed. The statistical evaluation was
car-ried out by standard regression analysis by
the method of least squares.
RESULTS
The results of 30 studies in 27 patients
comparing the creatinine clearance with
the single injection clearance with sodium
iothalamate J125 are listed in Table I in
§Nuclear Chicago Corporation, Des Plaines, Il-linois.
SINGLE-INJECTION CLEARANCE, USING SODIUM IOTRALAMATE P2’ (C,j)
Study Number
Age
(yr)
(U,,,gX V) measured
P1
(U8rg XV) expected
C,j C.01 Ccreag C8
Diagnosis
(mi/mm) t’J,, (mi/min/1.73 ni2)
Group A 40 44 33 42 48 23 64 100 74 100 74 79 103 94 86 69 8 56 40 36 50 60 25 59 119 67 109 65 78 75 65 112 72 7 0.71 1.10 0.92 0.84 0.80 0.92 1.08 0.84 1.10 0.92 1.14 1.01 1.37 1.45 0.77 0.96 1.14 1 2 3 4 5 6 7 8 9 10 Ii 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1 3 a a 6 7 8 9 10 10 10 10 11 12 12 14 a a 8 11 12 13 13 16 17 0.4 0.3 0.5 0.4 0.5 0.4 0.5 0.4 0.5 0.3 0.6 0.6 0.3 0.6 0.6 0.6 1.3 0.9 0.9 1.7 0.9 0.8 0.7 0.8 1.0 1.30 0.90 0.71 0.87 1.11 0.94 1.10 0.96 1.11 1.02 1.11 1.01 0.97 1.28 0.73 0.78 1.15 1 .03 1 .22 1.01 0.80 0.82 0.96 0.91 0.83 133 117 76 94 106 57 126 163 135 142 119 110 188 149 98 88 29 60 83 43 84 83 132 112 78 186 106 83 112 133 62 116 194 122 155 104 109 137 103 127 92 26 67 71 46 97 97 115 115 76 Nephrotic syndrome Nephrotic syndrome Post-transplant Nephrotic syndrome Hypertension Post-transplant Hematuria Hematuria Hematuria Nephrotic syndrome Chronic glomerulo-nephritis Hematuria Xephrotic syndrome Nephrotic syndrome Focal nephritis Post-transplant Hemolytic uremic syndrome Post-transplant Chronic glomerulo-nephritis Post-transplant Chronic glomerulo-nephritis Chronic glomerulo-nephritis Ilematuria Hypophosphatemia Chronic gloinerulo-nephritis
26 29 0.90
48 41 1.17
31 33 0.94
72 83 0.87
82 107 109 78 0.85 1.15 0.97 1.03 70 123 106 80 Group B*
26 2 4.0 1.63 2.7 3.8 0.71 12 16 Polycystic kidney
27 2 10.0 1.15 0.9 3.2 0.28 3 ii Nephrotic syndrome
end-stage
28 11 3.6 0.77 9.0 11.0 0.82 13 16 SubacuteGN
29 4.8 0.69 6.0 9.0 0.67 9 13 Subacute GN
30 14 15.2 0.26 0.9 3.2 0.28 1 4 Chronic GN
* Studies in patients with very low GFR.
GN-glornerulonephritis.
two different groups. The mean values of mean C, 66.3 ml/minute (S.D. 29.9). There
both methods are comparable in group A: is a good correlation in these 25 studies
*No simultaneous creatinine clearance obtained.
further define the limits of reliability of the
creatinine clearance, we selected and
com-pared those clearances where the serum
creatinine concentration was 0.7 mg/ 100 ml
or more with the single injection clearance.
This was done because the percent error
in the measurement of creatinine is greater
at low serum concentrations. The degree of
correlation was higher and the line of
re-gression was nearer the line of identity in
the 9 patients with a serum creatinine of
0.7 mg/100 ml or more
(
Cereat + 1.01x
- 1.2, r 0.97) . In the remaining16 patients of group A with a serum
creati-nine of 0.6 mg/lOOml or less, the correlation
is only fair (Ccreat = 0.82 X Csi + 11.5,
r = 0.84).
The patients in Group B had such a low
GFR, leading to considerable percent error
by both methods, that no statistical analysis
was done. However, agreement in terms of
absolute clearance was within 3 ml/minute.
The external counting was performed in
only four patients, but agreed well with
the simultaneous results from the plasma
counts (Table II).
The T112 was found to be between 43
and 143 minutes in all but two studies in
Group A (No. 17 and No. 20: both 5 hours)
and in those of Group B (5 to 40 hours). In
these seven studies the T was prolonged
due to low GFR, and the last plasma samples
had to be obtained later than usual.
DISCUSSION
Multiple errors are involved in the
deter-mination of creatinine clearance, especially
in children.#{176} For this reason, we looked for
an alternative method for the estimation of
GFR which could be done routinely in
chil-dren. Cohen, et al.b0 injected a single dose
of sodium iothalamate 1131 in children
dur-ing a constant infusion of inulin and
calcu-lated the clearances in the usual way (U X
VIP).
They compared the two clearancevalues obtained from each urine specimen
and found an excellent correlation, but
er-rors which could have arisen from
inaccu-rate urine collection cancelled out. There
was a wide scatter between the clearance
values in consecutive periods, and the mean
agreed only fairly well with the creatinine
clearance.
Since important errors can arise from
in-accurately timed urine collections, we used
a different method, which permitted
esti-mation of the GFR from the plasma
disap-pearance curve alone after a single injection
of a suitable substance. Constant
infu-sion clearances with sodium iothalamate
J125 have been shown to agree well with
those obtained with inulin.’8 This
sub-stance was chosen because it lends itself to
a simple and accurate quantitation using
doses of radiation that are within a range
quite acceptable for use in adults and
chil-dren with a renal disorder. Cohen,
et al.#{176}
estimate the total body irradiation in a
child weighing 30 kg, after injection of 10
Ci, to be 0.25 millirads with normal GFR
and 37 millirads with complete anuria.
These figures would be, roughly, three
times higher in a child weighing 10 kg. The
radioactivity to the patients with the usual
doses is thus minimal when compared with
other diagnostic and therapeutic
proce-dures, except in patients with very low
GFR. Estimates from our own radiation
safety committee are in agreement.
Since a labelled substance is used, errors
which arise from interfering chromogens
with chemical analysis of creatinine are
avoided. The accuracy of the single
injec-TABLE II
SINGLE INJECTION CLEARANCE CALCULATED FROM
EXTERNAL COL-NTING COMPARED WITH PLASMA SAMPLES AFrER SINGLE INJECTION OF SODIUM
IOTHALAMATE I IN Fovu PATIENTS
C,1(mi/mm)
Patient Age
.5 umber (yr) External Plasma Diagnosis
Counting
4
5
‘
‘
5 6
7 9
49 50
60 60
65 61
86 80
used and the calculations derived from it.
Experiments have shown4’5 that the
calcula-tion of GFR based on a single compartment
model, which assumes instantaneous
distri-bution of inulin ( or any other substance
handled like it) in its space of distribution
and simultaneous clearance by the kidney,
leads to considerable error-usually in
overestimation of GFR. Clinically, this
method may still be useful if one accepts
values not corresponding to true clearance
values.hl The open two-compartment
sys-tem of Sapirstein, et al. is based on the
assumption that inulin is instantaneously
distributed in the first compartment and
dif-fuses from it to a second compartment,
ac-cording to the gradient which exists. It is
si-multaneously cleared from the first volume
by the kidney. The disappearance curve
can be resolved into two exponential
func-tions; and, when plotted on semilogarithmic
paper, two slopes are obtained (Fig. 1).
Based on this two-compartment model,
sev-eral authors have, indeed, found a good
correlation between the single injection
clearance using sodium iothalamate P25 (or
another labelled substance handled like it),
and the constant-infusion inulin or
creati-nine clearance in dogs1’2 or humans.3’4 We
confirmed these findings in preliminary
studies in the rat, comparing the
single-in-jection clearance with sodium iothalamate
P25 to the constant-infusion clearance with
inulin. It was speculated that the single
in-jection clearance, since it is relatively
sim-ple and has been shown to provide a valid
estimate of GFR, might be especially
help-ful in children as an alternate method to
the creatinine clearance.
Our data show that the correlation
be-tween the creatinine clearance and single
injection clearance is significantly better in
those studies where the serum creatinine
concentration is 0.7 mg/ 100 ml or more
than in those where it is 0.6 mg/ 100 ml or
less. At low serum concentrations, the
preci-sion of the measurement is usually within ±
0.10 to 0.15 mg/ 100, and the relative
accu-able amounts of non-creatinine chromogens.
The range of error of calculated clearance
under these conditions is oven 20%.
The production of creatinine is
propor-tional to the total body muscle mass. This
explains why patients with severe muscle
wasting or infants and children have low
serum creatinine concentrations. Even with
markedly reduced GFR, their serum
creati-nine does not have to be elevated. Three
of the patients studied after renal
trans-plantation
(
studies 3, 6, and 16) areillus-trative examples of this.
Since the daily excretion of creatinine in
the urine shows a good correlation with the
body weight (or height), the values could
be predicted roughly and compared (using
the equation of Graystone6 with those
ac-tually obtained. By setting an arbitrary
limit of the measured over expected
creati-nine excretion ratio at 0.70, it was obvious
that in 8 of 33 studies (excluding those in
patients with very low GFR) the urine
col-lection was grossly incomplete.
The studies in patients with very low
GFR were not analyzed further because of
the considerable range of error of both
methods in this situation. Since the biologic
half-life of sodium iothalamate 1125 was
much prolonged and the hazard of
irradia-tion was increased, there seemed to be
fewer indications of the single injection
clearance in these patients. Supernormal
values of GFR obtained by both methods
were observed in four patients (studies 1,
8, 10, and 13), three of whom had the
ne-phrotic syndrome in which increased values
of GFR are sometimes found.12
One disadvantage of the single-injection
clearance is the need for frequent blood
sampling. The amount of plasma required
could be reduced to less than 1 ml per
samp’e if higher doses of the radioactive
substance svere injected, but this is not
de-sirable. The problem can be overcome
par-tially by the use of an external counter. The
results obtained in four patients agreed
simulta-neous plasma counts. However, this method
requires the patient to remain relatively
still during the counting.
IMPLICATIONS
The single-injection clearance with
so-dium iothalamate 1125 is a suitable method
for the routine estimation of GFR in
chil-dren, although it is more expensive and
time consuming than the creatinine
clear-ance. The latter appears to be useful when
urine collections are accurate and when the
serum creatinine concentration is 0.7 mg/
100 ml or more. The accuracy of collection
can be assessed by comparing the measured creatinine excretion with an expected value,
and it can be improved by repeated urine
collections.
The single-injection clearance is more
accurate than the creatinine clearance in
younger children, where a complete urine
collection is difficult to obtain, and when
the serum creatinine concentration is 0.6
mg/100 ml or lower. It is also helpful in
outpatients because of its short duration.
The number of plasma samples required
can be reduced to one by the use of an
ex-ternal counter.
REFERENCES
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N., Wakim, K. C., Orvis, A. L., and Owen,
C. A.: Plasmatic diatrizoate-”I disappear-ance and glornerular filtration rate in the dog. J. Physiol., 204:536, 1963.
2. Kountz, S. L., Yeh, S. H., Wood, J., Cohn, R.,
and Kriss, J. P.: Technetium-99m(V)-citrate
complex for estimation of glomerular
filtra-tion rate. Nature, 215:1397, 1967.
3. Farmer, C. D., Tauxe, W. N., Maher, F. T.,
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4. Truniger, B., Donath, A., and Kappeler, M.:
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5. Sapirstein, L. A., Vidt, D. C., Mandel, M. J., and Hanusek, C. : Volumes of distribution and
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Acknowledgment
