Parathyroid
Function
in Uremic
Children
With and
Without
Osteodystrophy
Betty S. Roof, M.D., Carolyn F. Piel, M.D., Linda Rames, M.D.,
Donald Potter, M.D., and Gilbert S. Gordan, M.D.
From the University of California, San Francisco
ABSTRACT. Circulating radioimmunoassayable parathyroid
hormone (iPTH) was not present in 30% (1 17) of 389 normal
children tested at ages from cord blood to 17 years. In the other 70% (272), mean iPTH was found to be 25 ± 0.7sl
eq/ml (± SEM; range, 0-53 ± 2 SD ). The iPTH levels
were elevated in 59% of 24 uremic children without radio-logic evidence of osteodystrophy in 94% uremic children with osteodystrophy. Infusion of calcium (10 mg/kg over three hours or 15 mg/kg over four hours ) in the children without osteodystrophv reduced the iPTH by nearly 50%; suppression was sustained for 9 to 20 hours. In uremic children with osteodystrophy, similar infusions failed to elevate the serum calcium concentration to the same degree and there was less suppression of iPTH which was not sus-tamed as long. Mean increment in serum calcium observed was 2.1 mg/100 ml with 10 mg/kg/3 hr and 3.4 for 15 mg/kg/4 hr in children without oteodystrophy, and 1.24 and 1.4 mg/100 nl in those with osteodystrophy for similar infusions. In both groups, calcium infusions lowered the concentration of serum magnesium and elevated the serum phosphate concentration. Tubular reabsorption of phosphate did not change consistently despite fall in serum iPTH levels. There was no correlation between suppressibility of para-thyroid function and serum creatinine level. In five children with osteodystrophy in whom calcium infusions did not suppress iPTH levels, nornial iPTH levels were achieved rapidly after successful renal transplantation. These data indicate that the secondary hyperparathyroidism of uremic children is suppressible and not autonomous. Pediatrics, 53: 404, 1974, RADIOIMMUNOASSAY, PARATHYROID HORMONE, NORMAL CHILDREN, UREMIC CHILDREN, OSTEODYSTROPHY,
CALCIUM INFUSIONS.
The availability of a highly specific reproducible
radioimmunoassay for determination of circulating
immunoreactive parathyroid hormone
(
iPTH)makes possible the study of parathyroid function
in normally growing children and in those with
uremia-a disease state in which increased
para-thyroid activity has long been inferred.
In 1966 Berson and Yalowl provided direct proof
of secondary hyperparathyroidism in chronic renal
failure by finding high plasma levels of iPTH in
uremic adults. Similar findings were reported by
Reiss et al.2 and Potts et al.
With the widespread use of chronic hemodialysis,
indefinite duration of end-stage kidney disease has
been achieved and development of more severe
osteodystrophy has been noted. Some have
sug-gested that hyperparathyroidism may become
au-tonomous in uremia and may even persist after
normal renal function is restored by successful
transplantation.46 However, Berson and Yalow,’
Reiss et al.2 and Potts et al.3 found that elevated
levels of iPTH in uremic adults can be suppressed
by short term calcium infusions. Reiss et al.2 noted
that the more severe the renal disease, the less the
decrease of serum iPTH following calcium infusion.
In 14 uremic adults on alternate-day dialysis studied
by Genuth et al.,7 normal or near-normal iPTH
levels were found in patients without bone disease,
while elevated levels suppressible with calcium
in-fusion were noted in those with osteodystrophy.
That iPTH circulates as heterogenous molecules
was first noted when Berson and Yalow in 19688
identified two different immunoreactive
parathy-roid peptides in plasma. One of these with a
circu-lating half-time (t/2) of 12 to 20 minutes
disap-peared rapidly after removal of a parathyroid
adenoma; the other had a longer t/2 of 1 to 1%
hours. This heterogeneity in plasma was
subse-quently shown to be due to a number of different
parathyroid hormone molecules which are
sepa-rable by physicochemical techniques that
differenti-(
Received February 13; revision accepted for publication October 23, 1973.)ADDRESS FOR REPRINTS: (B.S.R. ) Department of
EFFECT OF CALCIUM INFUSION ON SERUM PTH IN NORMAL & UREMIC CHILDREN
NORMAL I WITHOUTUREMIA CHILDREN BONE DISEASE 350
300
250
PTH 200
UREMIA WITH.
BONE
.S#{231}SEASE.
CALCIUM INFUSION RECO VERY
100
50 30
10#{128}-350
300
250
200
150
100
. 50
30
10 12 10 12 10 vi
SERUM CALCIUM mg/100 ml
FIG. 1. Comparison of suppression of iPTH by intravenous calcium in children who are normal, uremic without bone disease and uremic with bone disease. The short solid lines depict infusion of calcium, 10 mg/kg over three hours; the long solid lines, infusion of calcium, 15 mg/kg over four hours.
Uremic Children il eq/mIPTH
100
::
14
CALCIUM 12
mg/lOOml
10
6
PHOSPHORUS
mg/lOOmI 41:
I i I I I I I I I I
Ni
AM PM PM
1ORNIN1
IINFUSION
FIG. 2. Suppression of serum 1PTH by calcium infu7ions in
24 uremic children without radiologic evidence of
osteo-dystrophy. The infusions (solid lines) were given at night
(
10 mg/kg over three hours ) and in the morning (15 mg/kgover four hours ). (Points represent the mean ± SEM).
ate molecules of different size. Arnaud et al.9 have
reported in all patients with end-stage renal failure
a threefold to 20-fold increase of iPTH of 7,000
molecular weight
(mw
)
while only 70% have anincrease of 9,000 mw peptide. Habener et al.’#{176}used
antisera specific for the amino and carboxy
se-quences of iPTH and found a 1 : 1 relation of the
carboxy-amino terminals in the gland and its
efflu-ent blood, but in patients with primary
hyperpara-thyroidism, the relation was 6-20:1.
It is apparent that the amount of iPTH
recog-nized by any given antibody is necessarily a
func-tion of its ability to recognize the various circulating
molecules, as well as the concentration of each
present. Fortunately, the guinea pig antibody to
iPTH used routinely in our studies recognizes both
the biologically active and the longer circulating
sequence equally well. With radioimmunoassay,
parathyroid function was investigated in normal
and uremic children using calcium infusion to
deter-mine the responsiveness of the parathyroid glands.
SUBJECTS AND METHOD OF STUDY
Normal Children
Circulating iPTH and serum calcium levels were
measured in 389 normal children (from Well Child
Outpatient Clinic ), approximately ten of each sex
for each year to 17 years. Twenty-five cord bloods
were collected at time of delivery.
Six additional normal children 9 to 16 years of
age were given a calcium infusion 2.5 mg/kg
intra-venously over ten minutes following overnight
fast-ing. Serum samples were taken before and 30
minutes later for determination of iPTH and
cal-cium (Fig. 1).
Forty-one uremic children
(
ages 23 months to19 years 4 months
)
with chronic renal disease fromvarious causes were studied
(
36 in the PediatricClinical Research Center at Moffitt Hospital and
5 on the Metabolic Ward at the San Francisco
General Hospital
)
. Seventeen had roentgenevi-dence of osteodystrophy; 24 did not. Skeletal
sur-veys were reviewed in all children by radiologists
and three of us. (C.P., B.S.R., and G.S.C.). Skeletal
age was determined according to the standards of
Greulich and Pyle.”
Osteitis fibrosa was found in 15 children, rickets
in 4, osteosclerosis in 3 and retardation of bone
maturation in 8.
Subperiosteal resorption of the phalangeal cortex
was the most common radiologic abnormality
ob-served. No cystic changes were seen despite
ex-tensive generalized subperiosteal resorption.
On the metabolic wards, diet was controlled with
constant intake of protein and calcium throughout
the entire hospitalization. On the third day blood
was obtained for determination of calcium iPTH,
magnesium, inorganic phosphate, and creatinine at
the beginning and end of the calcium infusion (9
PM and midnight) and at 9 AM the following
morn-WITHOUT BONE DISEASE
MAGNESIUM
n-mg/lOOmI II I I I I
____
I 9
AM 9 1 5 912
AM PM PM PM M
11TURNAL
WITH BONE DISEASE
300
PTH
p1 eq/mI 200
100
I I I
uuuuu’-I I I
9 91
AM AMPMPM
RNIN1
1
INFUSION14
CALCIUM 12 mg/i 00 ml
10
PHOSPHORUS
mg/lOOmI
I I I I I I
______
MAGNESIUM 3r
mg/iOOmI
2I-I I I 1 I I I
_______
9 1 5 912
-AM PM PM PM M j NOCTURii1
INFUSION
_________
FIG. 3. Suppression of serum iPTH by calcium infusions in 17 uremic children with radiologic evidence of osteodystro-phy. Calcium infusions (solid lines ) are similar to those in
Fic. 1.
ing. Elevated phosphate levels were lowered by
aluminum salts prior to infusion. A two-hour urine
sample was collected for creatinine clearance
(Cr) and tubular reabsorption of phosphate (TRP)
the morning of and the morning after the infusion.
When the infusion was given in the morning, a
two-hour urine sample was collected from 7 to 9 AM
and again the following AM for the same studies.
Sera were obtained for the determinations noted at
the beginning and end of the infusion and at 4 and
20 hours after its completion. All infusions were
given as calcium gluconate diluted at least three
fold with isotonic saline.
Uremic Children Without Osteodystrophy
These 24 children received 24 infusions : 17 were
infused with 10 mg/kg over three hours
(
1 PM tomidnight
)
; 7 received 15 mg/kg over four hours(9 AM to 1 PM) (Figs. 1 and 2).
Uremic Children With Osteodystrophy
Of these 17 children, five had been maintained
on chronic dialysis for several months prior to
in-fusion and two were dialyzed on the day before
infusion. Nine patients were given ten infusions
(
10 mg of calcium per kilogram over three hours)from 9 PM to midnight. Eight received 15 mg of
calcium per kilogram over four hours from 9 AM
to 1 PM (Figs. 1 and 3).
Radioimmunoassay for iPTH
Serum iPTH was measured in our laboratory by
the radioimmunoassay method of Berson and Yalow
using talc to separate antibody-bound
(
B)
fromfree
(
F)
tracer fractions.’2 Protein concentrationduring incubation was kept constant with serum
added from patients with surgical
hypoparathyroid-ism. The antiserum, developed by immunizing
guinea pigs with bovine PTH (bPTH
)
reactsI I I equally well with iPTH from human adenomas,
with iPTH in serum of patients with primary
hyperparathyroidism, with iPTH in serum of
r8_1%1i
uremic patients and with synthetic moleculecon-taming the first 34 amino acids of bPTH. In this
assay, 0.5 ng of 1,000 U/mg of bPTH reduces the
ratio of antibody bound to unbound ‘2’I-labelled
bPTH
(
B/F)
by 30%; 0.5 ng of a 3,000 U/mgbPTH (prepared in our laboratory) gives 84%
de-pression. Values are expressed as equivalents of a
preparation of human PTH from an adenoma.
Twenty microliters have immunoreactivity
equiva-lent to that of 1.0 ng of bPTH (Wilson 1,000 U/mg)
or 0.8 ng of a partially purified human PTH kindly
provided by Dr. C. Arnaud.
Chemical Methods
Serum sodium, potassium, phosphate, creatinine,
blood urea nitrogen
(
BUN),
and urinary phosphateand creatinine were measured by Technicon
auto-analyzer.’3 Calcium was determined by flame
spec-trophotometric technique,’4 bicarbonate
(
HCO3)in Natelson gasometer,’5 chloride by Amico-Cotlove
chloride titrator,’#{176} magnesium by Perkin-Elmer
atomic absorption,17 alkaline phosphatase by
Bes-sey-Lowry method with Sigma kit,18 serum globulin
by modification of Dow kit procedure’9 and
albu-mm estimated from difference between total
pro-tein and globulin. Total protein was measured by
the Biuret method.2#{176}
RESULTS
iPTH in Normal Children
Measurable 1PTH levels were found in 70% of
normal children. The mean level was 25± O.7sl
eq/ml (mean ± SEM ). Values in the first two
years of life were approximately double those found
in cord blood
(
15 ± 3.d eq/ml) and higher thanin older children. The average serum calcium level
was 10.46 ± 0.07 which is higher than in adults,
especially in the first two years. In the normal
children in whom calcium infusions were
per-formed, iPTH levels were suppressed by the
in-fusion in three and unchanged in two in whom
initial levels were very low (Fig. 1).
Uremic Children Without Bone Disease
significantly elevated compared with values of
nor-mal children. Fifty-nine percent of the children
without radiologic evidence of osteodystrophy had
elevated preinfusion iPTH levels; the others had
normal levels. Infusion of calcium, 10 mg/kg over
three hours, raised serum calcium 2.2 ± 0.45 mg/
100 ml (mean ± SEM
)
; 15 mg/kg over four hoursraised serum calcium 3.5 ± 0.69.
In all the children with circulating iPTH > 53jsI
eq/mi and in whom hypercalcemia was induced,
iPTH was suppressed 40% to 100% and remained
suppressed 9 and 20 hours later. In ten, iPTH
sup-pression persisted after the serum calcium returned
to or below preinfusion levels. In three of seven
children infused with calcium from 9 AM to 1 PM,
serum iPTH remained suppressed 4 to 20 hours,
although the serum calcium had returned to near
basal levels. No suppression occurred in the
re-maining four patients, two of whom had low normal
iPTH levels prior to infusion. There was no
signifi-cant difference
(
Student’s t test) between theserum creatinine, BUN, alkaline phosphatase and
Cr Of the groups infused at night or in the morning.
Uremic Children With Osteodystrophy
Children with osteodystrophy had higher levels
of iPTH than those without radiologic evidence of
bone disease; lower values were found in six
pa-tients whose sera were stored for two years before
being assayed. The iPTH levels were also lower in
children who had received calcium and/or vitamin
D. Greatly elevated levels were still present the
day of infusion in two children who were dialyzed
the preceding day.
Suppression of iPTH was achieved by small but
significant
(
p < 0.01)
increases in serum calcium,averaging 1.5 ± 0.25
mg/100
ml from infusion of10 mg/kg over three hours and 1.40 ± 0.33 mg/100
ml from 15 mg/kg over four hours.
In three patients, iPTH suppression exceeded 40%
and was still present nine hours later. In six
hypo-calcemic patients, iPTH was suppressed > 30%
when the serum calcium level was raised to normal
levels while in five normocalcemic children 1PTH
was suppressed < 30% when calcium levels were
made hypercalcemic by infusion in one child who
had received pharmacologic doses of vitamin D,
preinfusion iPTH values were normal, although
radiologic evidence of bone disease still persisted.
In comparing parathyroid responses in children
with and without osteodystrophy, a similar
incre-ment of serum calcium (1.9 mg/100 ml) suppressed
iPTH 100% in a child without bone disease, but
only 23 to 54% in four children with bone disease.
A greater calcium increment, 3.4 mg/100 ml, caused
more equivalent suppression: 56% in a child without
osteodystrophy and 45% in one with bone disease.
Other Laboratory Values
In the children without osteodystrophy serum
phosphate was within the normal range morning
and evening on the day of infusion. Nocturnal
cal-cium infusion produced a rise in mean serum
of 0.45 mg/100 ml, higher than that after morning
infusion. There was no correlation between the
in-crease in serum phosphate concentration and the
de-gree of suppression of iPTH or increase in serum
cal-cium concentration. In children with osteodystrophy,
the mean level of phosphate was lower at 9 PM than
at 9 AM. After nocturnal infusion of calcium, the
phosphate level increased in all except two, but
de-creased in four of five with morning infusion. Over
all, the increases in serum phosphate level produced
by calcium infusion were subnormal in these
chil-dren. Tubular reabsorption of phosphate
(
TRP)did not change significantly although calcium
in-fusion suppressed iPTH levels in both groups.
Alkaline phosphatase was elevated in all children
without radiologic evidence of bone disease. The
elevation of alkaline phosphatase was greater in
those with osteodystrophy in whom azotemia was
more severe
(
p < 0.05).In children without osteodystrophy, the mean
magnesium concentration was within normal limits
at all times, without diurnal variation. Nocturnal
infusion of calcium decreased the level of
mag-nesium in six of 12 children followed by a return
to preinfusion values at nine hours; morning
in-fusion of calcium decreased the mean magnesium
level. In one third of the children, serum
mag-nesium levels were above normal although none
were taking magnesium medication. The overall
change in magnesium concentration with calcium
infusion was significant (p < 0.02). In children
with osteodystrophy, the mean magnesium level
be-fore infusion was higher than in those without bone
disease (p < 0.01). In them, calcium infusion
low-ered magnesium levels slightly but not significantly.
Mean values for concentration of sodium,
potas-sium, chloride, total protein, albumin and globulin
in both groups of children were within normal
limits, but levels of bicarbonate were markedly
re-duced. Hyperchioremic acidosis was present in
seven of 24 without osteodystrophy and five of 17
with osteodystrophy; only one had primary renal
tubular acidosis.
DISCUSSION
The radioimmunoassay used in these studies
detects measurable levels of circulating iPTH in
children-70%-have measurable levels, a difference which may
relate to a higher milk intake in children compared
with adults. Both serum calcium and iPTH levels
were higher in these children than in adults. Similar
findings have been reported by Arnaud et al.,2’
perhaps reflecting more rapid growth and bone
re-modeling in children.
The higher concentrations of iPTH in uremic
children with osteodystrophy than in those without
radiologic evidence of bone disease are similar to
observations in adults. The degree of parathyroid
hyperfunction correlates with severity and duration
of uremia.’3 We found elevated levels of iPTH in
43% of uremic children in whom there was no
radio-logic evidence of hyperparathyroidism, while
Genuth et al.7 reported normal levels of iPTH in
uremic adults without bone disease. Their patients
were on alternate-day hemodialysis which, with
appropriate calcium concentrations, will suppress
parathyroid overactivity.
Suppression of the elevated circulating iPTH
levels in uremic children by infused calcium reflects
physiologic responsiveness of the hyperfunctioning
parathyroid glands. The smaller increase of serum
calcium in the children with osteodystrophy
com-pared with those without radiologic evidence of
bone disease reflects increased avidity for calcium
by the more severely involved bones. Since
suppres-sion of iPTH was less and not sustained in children
with osteodystrophy, the presence of larger masses
of hyperfunctioning parathyroid tissue is indicated.
Ten to 15 mg/kg of calcium infused for three to
four hours was not sufficient to suppress the
ele-vated iPTH levels in five children. That their
para-thyroid glands were not “autonomous” was shown
when all five rapidly had normal iPTH levels after
successful renal homotransplantation. Reiss et al.2
reported an inverse relationship between serum
creatinine concentration and suppressibility of
ser-um iPTH by calcium infusion (4 mg/kg over six
hours). In our children, suppressibility related more
closely to presence or absence of osteodystrophy
than to serum concentration of creatinine.
Calcium infusion using saline as diluent given AM
or PM will raise serum phosphate levels in normal
adults. Nocturnal calcium infusions elevated serum
calcium and suppressed iPTH levels in both groups
of children, but neither significantly altered serum
phosphate concentration nor TRP, clearly
dissociat-ing these endpoints from parathyroid function.
Morning calcium infusions failed to raise serum
phosphate levels in children with osteodystrophy.
Lack of elevation of serum phosphate with calcium
infusions has previously been observed in primary
hyperparathyroidism and in hypoparathyroidism,22
findings which support our observation.
The direct relationship of serum iPTH to alkaline
phosphatase has been noted by Oreopoulos et al.23
Vitamin D therapy in our children gradually
de-creased elevated serum iPTH and alkaline
phospha-tase levels. Statistical analysis showed only
sug-gestive correlation between elevation of serum
alka-line phosphatase and serum iPTH, an observation
probably influenced by the medical therapy.
Calcium infusion decreased magnesium levels
significantly only in the children without
osteo-dystrophy. The difference in response may have
resulted from failure to achieve similar elevations
of serum calcium in both groups of children and/or
may have been influenced by the fact that more
children with osteodystrophy were on chronic
hemodialysis which may have diminished their
magnesium pool and thereby altered the response
to calcium infusion.
The most common radiologic evidence of bone
disease in these children was osteitis fibrosa. Similar
experiences have been reported by Genuth et al.7
and Meema et al.2 In contrast, Kaye and
Silver-man25 in Montreal found osteosclerosis most
corn-monly in their patients, and Stanbury26 in the
United Kingdom found osteomalacia most
corn-monly. Variation in vitamin D intake and/or
therapy with calcium salts and aluminum hydroxide
gel (Amphojel) may explain these differences.
In summary, iPTH levels in uremic children,
especially with osteodystrophy, were greatly
ele-vated compared with levels in normal children.
These were readily lowered by infusion of calcium.
The increment in serum calcium required to
sup-press iPTH was surprisingly small-mean 2.1-3.4
mg/100 ml in patients without osteodystrophy and
mean 1.24-1.4 mg/100 ml in those with
osteodystro-phy. The few patients whose iPTH levels were not
suppressible subsequently responded to successful
renal transplantation by normalization of iPTH
levels. It is concluded that the secondary
hyperpara-thyroidism of uremic children is not autonomous.
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ACKNOWLEDGMENT
Studies were supported by Public Health Service grants
CA-11087 and AM-12637 from the National Institutes of
Health, and conducted in the Pediatric Clinical Research Center at Moffitt Hospital and in the General Clinical
Re-search Center at San Francisco General Hospital, supported,
respectively, by Public Health Service grants RR-99 from
