European Urology
c.c. Schulman, Brussels
Editor:
Research Paper
Reprint
Publisher: S.Karger AG, Basel
Printed in Switzerland
F. Grases
J. G. M arch
A. Cante
A. Casta-Bauzá
Department ofChemistry, Faculty of
Sciences, University ofBalearic Islands, and
Urology Unity, Son Dureta Hospital,
Palma de Mallorca, Spain
EurUroI1993;24:381-386
New Aspects on the
Composition, Structure and
Origin of Calcium Oxalate
Monohydrate Calculi
..................................................................................................
Key Words
Abstract
Calcium oxalate monohydrate
calculi
Phosphates
H ypoci tra turia
Hypercalci uria
Urinary pH
In this paper a thorough study on the composition and structure of calcium
oxalate monohydrate (COM) papillary calculi is presented. In 86.4% of these
calculi, small amounts of phosphates were detected and gene rally located at
the calculi coreo This demonstrates the importance ofphosphates as the heterogeneous nucleus of 'pure' COM calculi. Study of the main biochemical
parameters ofthese patients showed that the most frequent biochemical alteration was associated with hypocitraturia (25 %), whereas hypercalciuria and/or
hyperoxaluria were detected in very few cases. With respect to the urinary pH
values, 70% ofthe patients presented values lower than 6 and 30% higher than
6. These facts indicate that in a number of cases the formation of phosphates is
not the result of persistent high urinary pH values, and the presence of occasional papillary microinfections must be suspected. It is clear that, by avoiding
the formation of heterogeneous phosphate nuclei, 'pure' COM calculi would
not develop, and consequently therapies for these individuals under these conditions must take this into account.
Introduction
It is a clearly established and accepted fact that, considering the levels of calcium and oxalate found in urine,
calcium oxalate crystals cannot be formed through homogeneous nucleation of this salt in this medium [1-4].
Therefore, some sort of preformed solid particle must act
as the heterogeneous nucleus. In some cases, the presence
ofuric acid, phosphates or even some drugs or metabolite
drug has been clearly identified as the heterogeneous
nucleus and origin ofthe calculus [5-8].
To analyze these aspects, it is necessary to distinguish
between calcium oxalate dihydrate (COD) and calcium
oxalate monohydreate (COM) calculi. COD calculi have
frequently been found to be associated with phosphates.
Nevertheless, a large quantity of calcium oxalate calculi
(mainly COM) has been classified as 'pure' calculi in such
a way that the heterogeneous nucleus responsible for the
origin of the calculus remains unknown, and important
data that could contribute to the clarification of the etiology of the disease have been omitted. In this paper we
present a thorough study ofthe composition and structure
of 'pure' COM papillary calculi with the aim of detecting
the origin and cause of their formation.
Dr. F. Grases
Department of Chemistry
Faculty ofScicnce
University of Ba!earic Islands
E-07071 Palma de Mallorca (Spain)
© 1993 S. Kargcr AG, Base!
0302-2838/93/0243-0381
$2.75/0
Table 1. Classification
of studied calculi
and distribution
Composition
n
%
'Pure' COM
'Pure' COD
Calcium oxalates and
phosphates
COM and uric acid or urates
Phosphates
Uric acid or urates
Other components
84
47
25.1
14.1
90
4
69
36
4
27.0
1.2
20.6
10.8
1.2
Results
The composition (%) of the 334 calculi studied (belonging to 314 patients) appears in table 1. As can be seen,
'pure' COM calculi (25.1 %) are the most common. Calcium oxalates make up 67.4% of the total calculi; phosphates (without calcium oxalate), 20.6%, and uric acid
and urates, 10.8%.
Detailed analysis of 'pure' COM calculus composition
using infrared spectroscopy and assisted by a stereoscopic
microscope is shown in table 2. As can be seen, in 86.4%
of the calculi small amounts of phosphates were detected.
In the remaining 13.6% no other components could be
detected, probably because the amount was too small to
permit detection.
Figure 1 shows a typical infrared spectrum in which
the presence of phosphates as a minor component was
identified.
Table 2. Analysis of calculi classified as
'pure' COM and COD by infrared spectroscopy
%
34.1
86.4
13.6
65.9
Composition
COM exclusively
exclusively
COD
II
70
15
n29
The presence of spherulitic or plate-like phosphate
crystals was detected in a number of calculi and located in
the core ofthe calculus (fig. 2, 3).
The main urinary biochemical parameters of 67 patients with 'pure' COM calculi are summarized in table 3.
As can be seen, the most frequent biochemical alteration
corresponded to hypocitraturia (in around 25% of individuals), whereas hypercalciuria and/or hyperoxaluria
and/or hyperphosphaturia and/or hyperuricosuria were
only detected in very few cases.
Patients and Methods
Discussion and Conclusion
Renal stones formed by 314 patients were studied using a stereoscopic microscope and an infrared spectroscope. The calculi were
classified according to their composition into 7 groups: (1) 'pure'
COM (COM being the main component, phosphates cannot be differentiated using a stereoscopic microscope); (2) 'pure' COD (COD
being the main component, phosphates cannot be differentiated
using a stereoscopic microscope); (3) calcium oxalates and phosphates; (4) COM and uric acid or urates; (5) phosphates; (6) uric acid
or urates, and (7) other components.
Only 'pure' COM calculi were selected for this study. All were
studied by infrared spectroscopy and a number of them were al so
studied by scanning electron microscopy and EDAX. The main urinary biochemical parameters were determined in 67 patients. The
subjects were on a free diet at the time ofurine collection and none of
them were undergoing pharmacologic treatment of any kind.
Metabolic evaluation included calcium, oxalate, uric acid and
citrate. Urinary calcium was determined by atomic absorption spectroscopy (Perkin-Elmer 703); uric acid, citrate and oxalate by Boehringer Mannheim kit s No. 704156, 139076 and 755699, respectively.
The composition ofthe calculi was determined by infrared spectroscopy with potassium bromide discs using a Perkin-Elmer 683. Stone
fragments were studied using a Hitachi S-530 scanning electron
microscope equipped with the EDAX analytical device.
382
As stated in the Results, in 86.4% ofthose classified as
'pure' COM renal stones, the presence oflow quantities of
phosphate was detected. Phosphate crystals were also
located in the stone core (fig. 2, 3.) These analytical results
indicate that the crystallization of phosphate salts can
play an important rol e in the core formation of 'pure'
COM stones, mainly of both of the following are considered: (1) phosphate salts can act as an effective heterogeneous nucleus of calcium oxalate, and (2) due to supersaturation conditions in human urine, the homogeneous
nucleation of calcium oxalate is not probable.
When phosphate is present in large amounts and
mixed with calcium oxalate in the same calculus, its structure is clearly different from that found in so-called 'pure'
COM renal calculi. Calcium oxalate and phosphate mixed
calculi are made up of alternative layers of calcium oxalate (monohydrate or dihydrate) and calcium phosphates,
which can be clearly detected and identified using a ste-
Grases/March/Conte/Costa-
Bauzá
Studies on Calcium Oxalate Papillary
Calculi
reoscopic microscope. Generally the phosphates are more
abundant than calcium oxalates. This type of mixed calculi is very frequent in all types of hypercalciuria and
hyperparathyroidism [9]. The so-called 'pure' COM calculi are generally papillary, the structure ofwhich is made
up of a core component of loosely arranged, twinned and
intergrown crystals of plate-like and/or columnar shape
and partic1es of 'rosette' form with considerable space
between the crystals in some cases, or compact structure
in others. A substantial amount of organic matrix appeared at the core boundary, often in the form of amorphous plates. The outer striated layer of the COM stone
consisted of tightly packed columnar crystals originating
on this matrix. The stone core was located near the stone
surface that was attached to the kidney wall and contained foreign partic1es that act as the heterogeneous
nuc1eusof calcium oxalate crystals [10].
On the other hand, the main urinary biochemical
parameters (table 3) show several interesting facts. It can
be seen that most ofthe 'pure' COM stone formers exhibited neither hypercalciuria nor hyperoxaluria and consequently can be considered as 'idiopathic'. Nevertheless,
an important number of them (25%) had low citrate
excretion (lover than 250 mg/24 h). With respect to the
urinary pH, 70% had values below 6 and 30% above 6. In
consideration ofthese facts, the residence time ofurine in
a physiologically normal kidney, and the kidney inner
wall protection from solid depositions by a continuously
renewed uromucoid layer, it can be stated that in a number of cases the formation of phosphate deposits is not
just a consequence ofpersistently high urinary pH values.
Under such circumstances the existence of occasional
papillary microinfections could justify the local destruction ofthe uroepithelium and the increase in urinary pH.
On such an assumption of bacterial attack, a local pH
increase in the urine surrounding the infected focus could
take place, and consequently the nuc1eation of magnesium ammonium phosphate or a mixture of calcium
phosphates on the damaged wall is facilitated. Moreover,
even under favorable conditions to develop a phosphate
cradle (hea1thy people with urinary pH values of > 6 or
people with urinary infection), the process can be avoided
or delayed by the effective action of urinary inhibitions
such as citrate.
The above facts enable the proposition of a formation
mechanism of an important number of 'pure' COM calculi as follows. In a decisive first step, as a consequence of
microinfections or pH values that permit phosphate precipitation, and in a not well protected uroepithelium
papillary zone (i.e. damaged as a consequence ofbacterial
4,000
2,000
1,500
1,000
500
-1
cm
2
Fig. 1. Infrared spectrum of a 'pure' COM calculus in which the
presence of very low quantities of phosphates can be clearly detected.
Fig. 2. Spherulitic crystaIs of phosphate detected in the calculus
coreo The presence ofCOD can be clearly seen.
Fig. 3. Compact phosphate crystals detected in the calculus coreo
The presence of organic matter is seen.
383
211
476
414
205
249
212
269
474
674
603
418
123
169
278
331
327
361
655
376
-
211
458
205
21.2
272
224
157
5.21
5.75
177
377
22
127
447
mIU
657
142
422
214
74.5
382
169
12.4
4158
17
452
150
121
17.5
793
245
422
44
31.8
33.6
430
48.2
410
667
314
300
329
456
18.7
545
12.1
180
7.7
63
39.3
55.0
977
89.8
69.9
981
819
380
20.8
418
362
580
399
551
540
23.2
570
19.3
217
89
6.46
5.39
6.57
5.96
5.99
6.55
5.87
5.06
5.06950
71.0
60.6
38.4
31.4
216
156
65.4
37.4
46.4
569
540
838
70.2
878
323
879
668
68.5
81.2
602
976
257
202
310
281
745
406
349
413
307
460
697
404
278
436
673
709
346
236
597
22.9
317
22.1
203
246
536
31.3
12.9
11.8
18.1
13.3
1.250
19.8
11.9
4.3
36
78
9.4
202
139
111
164
192
759
85
91
85
76
321
26.0
473
6.0
106
71.1
36.3
18.9
60.5
367
50.3
887
80.1
79.7
969
696
338
451
382
367
839
28.3
Diuresis
497
743
496
455
325
153
12.7
516
179
555
12.3
561
609
18.2
17.0
11.2
89
245
Ca
323
99
43
ric acid Creatinine
Citrate
84.8
59.3
53.8
448
22.8
781
449
21.3
569
360
17.2
105
73
50.8
284
371
17.3
55.2
53.7
41.1
83.1
226
430
423
287
24.0
769
35.4
22.2
644
219
2mg/I
28
95
33
97
65
44.8
21.9
320
69.0
52.9
346
870
86.7
208
292
223
11.0
470
955
352
566
29.8
32.6
10.2
176
8.7
264
154
59
54
49.1
52.4
59.9
52.0
944
997
430
267
632
478
398
27.3
716
498
318
505
101
102
131
1867
6.2
43.5
35.2
63.5
808
331
225
350
251
567
773
15.8
88 urinary
60.0
330
940
10.3
120.9
506
186
47.7
71.4
368
805
347
14.9
200
3130
31.9
77
80
31.7
56.5
590
262
402
12.0
51
41.7
486
612
16.0
153
54.1
933
635
96
87
25.7
652
249
16.9
59.7
302
407
79
6.49
6.25
5.51
6.39
6.07
5.42
6.08
5.56
5.22
5.62
5.51
5.69
4.85
5.72
5.98
6.51
5.18
5.68
5.23
4.97
6.63
5.67825
5.64
6.70
5.38
6.22
5.29
5.261,300
2,100
3,475
5.08
5.30
1,580
1,665
1,114
23,7
2,600
2,180
1,290
1,630
6.53
2,750
1,445
5.43
5.35
5.94
2,130
2,650
1,265
1,280
1,500
1,885
5.49
5.38
6.05
6.54
5.13
1,815
1,130
1,160
6.95
1,040
1,700
1,660
1,519
2,700
1,530
5.26
1,715
1,900
1,400
5.58
2,315
1,465
1,050
1,450
5.54
2,200
5.28
1,600
1,883
1,565
Table 6.48
pH
3.
Mg
Phosphate
Main
Oxalate
parameters
corresponding
to 'pure' COM stone formers
1,070
1,300
1,550
1,230
2,120
2,075
1,160
1,365
1,840
mg/I
mg/I
2,373
2,300
1,100
2,030
Patient
384
Grases/March/Conte/Costa-
Bauzá
Studies on Ca1cium Oxalate Papillary
Calcu1i
388
b
-
224
13.2
427
127
25.6
48.3
32.4
308
358
54.9
62.9
53.9
66.8
410
933
71.6
730
767
482
208
259
301
291
648
428
488
382
598
557
693
336
507
18.3
19.4
[0.5
194
6.0
622.8
20.6
3[25
117
150
140
965
70
54
91
85
80
72 the
52.9
55.7
923
476
261
Diuresis
775
703
13.3
121
Creatinine
Citrate
U
ric components
acidofphosphates
5.58
5.53
4.85
6.01
5.95
7.21
5.41
5.12
557
8.5
1l.3
Ca
Calculi3pH
1,740
1,327
4.90
1,150
6.68
in
2,925
2,900
1,900
1,650
1,730
1,500
1,315
which
nomiother
were detected.
1,070
1,034
Table
(continued)
Mg
mg/I
mg/l
mg/I
Phosphate
mg/I
Oxalate
presence
as a minar component
was detected.
Patient
A
1
2
A
3
4
B
Fig.4. Scheme of the COM calculi formation steps.
385
attack), several phosphate crystals attached to the wall
start the calculus formation. On these phosphates, eOD
crystals can easily nucleate, as demonstrated in a previous
paper [11], or the phosphates can be covered by organic
material. On eOD crystals or organic material, eOM
crystals can easily nucleate, initiating genesis of the stone
core by primary agglomeration [12]. The deposit of organic material on this core stops its growth and enables
the beginning of the growth of the compact columnar
eOM zone [10]. This process is shown in figure 4. Figures
2 and 3 show 'pure' eOM renal stones whose structures
agree with the proposed hypothesis.
In conclusion, the important role that pH and/or
microinfections in conjunction with not well protected
inner kidney walls can play in 'pure' eOM calculogenesis
must be emphasized. The importance of phosphates as
heterogeneous nuclei of calcium oxalate crystals, and consequently, as the initiator of 'pure' eOM calculi formation is shown. Moreover, it is clear that by avoiding the
formation of heterogeneous phosphate nuclei in such
cases, calcium oxalate calculus should not develop. eonsidering the above facts, therapies assigned to individuals
with these conditions should make changes in or precisely
control the urinary pH and/or include antiseptic therapy,
and if possible, increase the protective uromucoid layer
that covers the inner walls of the kidney.
Acknowledgement
Financial support fram the Dirección General de Investigación
Científica y Técnica, grant PB 89-0423, is gratefully acknowledged .
.....................................................................................................................................................
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Studies on Calcium Oxalate Papillary
Calculi