A Simple Method to Type the Urinary Stones

The main aim of this study was to find an alternative method to type the urinary stones, which do not comply with the available method. For this study 100 stones were selected and were analysed by wet chemical method. The compositions of randomly selected 10 stones each among the stones typed based on the available and the new method were crosschecked by Fourier Transform infrared Spectroscopy (FTIR) method. Among the 100 stones, 46 stones were of Category I [21 stones Uric acid/Urate, 13 stones Oxalate, 12 stones Phosphate] while five were of Category II stones. Rest 49 stones, which cannot be typed by the available method, were typed by considering the ratios between the characterizing and indicating anions. To type the Oxalate stones, Oxalate to Urate ratio between 16.8:1 and 67.7:1; Urate stones, Urate to Oxalate ratio between 0.7:1 and 101.7:1 and Non- infection Phosphate stones, Phosphate to Oxalate ratio between 0.4:1 and 24.4:1 were considered. Based on the newly proposed method majority of the stones were of Oxalate type (n=41). Based on both the methods of stone typing, of the total 100 stones, 54 stones were Oxalate type, 25 stones were Uric acid/Urate type, 16 stones were Non-infectious Phosphate stones and 05 were Infectious stones. The compositions of the randomly selected ten stones of each typed from the available and the newly proposed method were similar to the results obtained by FTIR method. This study indicated that, the new method could be used as an alternative method to type the stones.


Introduction
Urinary stones are polycrystalline aggregates composed of varying amounts of crystalloid and a small amount of organic matrix, 1 and they are formed at any part of the urinary tract. 2,3 Urinary stone formation is one of the most prevalent urologic diseases in Asia ranging from 1-5%. 4,5 Urinary stone analysis is carried out by different methods; such as chemical analysis, [6][7][8] thermo gravimetry, 9 polarization microscopy, 10 scanning electron microscopy (SEM), 10 powder X-ray diffraction (XRD), 10-12 spectroscopy, [12][13][14] and Fourier Transform Infrared Spectroscopy (FTIR). 15,16 The chemical analysis is commonly known as wet chemical method and is one of the most widely used approaches for stone analysis. It can determine the presence of individual ions and radicals. 6,14 The wet chemical methods usually use the quantitative analytical methods for the analysis of chemical components in the blood and urine. The components analysed by these methods are used to calculate the amounts of chemical compounds present in the stones. 6,17 To type the urinary stones, the method described by Abdel-Halim, et al. 17 is commonly used. In the method, the urinary stones are typed based on characterizing and the indicating ions. Furthermore, have described a method to type the urinary stones by cluster analysis of ionic composition data. 18 In this study an alternative method was developed to type the stones which cannot be categorized based on the method described by Abdel-Halim et al. 17

Materials:
The reagent kits for the estimation of Calcium, Magnesium, Urate/Uric acid, Inorganic Phosphate and Oxalate were from Diagnosticum Zrt., Swiss Hungarian Joint Venture Company, Hungary. All the other chemicals used were of analytical grade.

Sample collection and storage:
For this study, 100 urinary stones from patients who underwent surgical interventions at Genitourinary Surgical Unit of Teaching Hospital, Jaffna were collected. The collected samples were placed on sterile gauze to air dry, and transferred into a sterile glass bottle bearing the patient details. All the specimens were washed with deionized water to remove the loose debris such as blood, mucous and casts, bile and debris and then dried in an oven to 60°C for five hours or overnight 17,19 and stored at 4°C. Preparation of the Urinary stones for analysis: Ground urinary stone samples (powder, 20 mg) were dissolved in 2 ml of 6N HCl with slight warming 6 and those were insoluble in 6N HCl were dissolved either in 6 g/L Li 2 CO 3 [20] or in a mixture of 6 g/L Li 2 CO 3 and 6N HCl. Total volume of the dissolved stone preparations was made up to 10 ml with deionized water.

Analytical Methods
Wet Chemical Methods: The stone samples were analysed by wet chemical methods for Calcium 21  Classification of Urinary stones: The method described by Abdel-Halim, et al. 17 was used to type the urinary stones.
Fourier Transform Infrared Spectroscopy (FTIR) method: The fine homogenous stone powder of the samples was analysed by FTIR method. 16

Results
One hundred urinary stones collected from the Genitourinary Surgical Unit of Teaching Hospital, Jaffna were categorised based on Abdel-Halim et al. 17 and to the stones which cannot be typed an easy alternative method was suggested.

Typing based on characterizing ion:
The stones selected were typed by considering the characterizing ions and the indicating ion/s. 17 Among the 100 stones, 51 stones had the compositions to match the typing described by

Sub typing based on indicating ion/s:
The typed Category I stones (n=46) were further sub-typed based on the indicating ions 17 . Of the 21 Uric acid/Urate stones, majority of the stones (n=14) were of UrI 4 and all the Oxalate stones (n=13) were of the subgroup; OxI 3. Among the 12 Phosphate stones (Non-infectious), 05 were of PhI 1 and 07 were of PhI 2 ( Table 1).

Typing of the stones based on the new method:
Among the typed 51 stones 46 stones were of Category I and rest 5 stones were of Category II. The characterizing ion of Category I stone type had different percentage of indicating ion/s. 17 Considering the ionic compositions of the 46 Category I stones, the new method of stone typing is described by calculating the ratios between the characterizing and indicating ions (  Oxalate sub types 1, 2 and 3 and Non-infectious Phosphates sub types 1 and 2, the possible ranges between the characterizing and indicating ions were calculated ( Table 3). The 49 stones were further sub-typed based on the ratios between the characterizing ion and indicating ion/s ranges given for the sub types by Abdel-Halim, et al. 17 On the basis of the calculation, of the four Uric acid/Urate stones, three stones were of UrI 2; all the Oxalate stones (n=41) were of the sub type; OxI 3 and all four Phosphate stones (Non-infectious) were of PhI 1 (Table 3). Among the stones typed based on the method suggested in this paper, the Magnesium stones were not found.

Confirming the types of the stones based on the Fourier Transform Infrared Spectroscopy (FTIR) method:
To confirm the possibility of using the method proposed in this paper to type the stones, the stones were analysed by the FTIR method. 16 For this purpose, ten stones among the 51 typed [based on Abdel-Halim, et al. 17 ] and another ten stones among the 49 non-typed stones were randomly selected for analysis by FTIR.  17 . b The minimum ratios between the characterizing and indicating anions present in the stones. c The maximum ratios between the characterizing and indicating anions present in the stones. d Typing of the stones based on the new method.  The results indicated that the new alternative method proposed in this paper is in good agreement with that described by Abdel-Halim, et al. 17 to type the urinary stones and with the results obtained with the FTIR. Hence the method proposed in this paper is useful for future typing of the stones especially those which are analysed by wet chemical method and do not have the anion concentrations to comply with Abdel-Halim et al. 17

Discussion
Main objective of this study was to type the 100 urinary stones obtained from the patients who underwent surgical interventions at Genitourinary Surgical Unit of Teaching Hospital, Jaffna using a method described by Abdel-Halim, et al 17 and finding an easy alternative method to type the stones which do not comply with the said classification method. As there are no relevant literature available to suggest the stone typing other than those described by Abdel-Halim, et al. 17 an attempt was made to study the typing in accordance with their typing while suggesting an alternative calculation. Furthermore the other methods used for the stone typing are expensive and need sophisticated equipment, which are difficult for the third world country researchers to purchase.
The method used by Abdel-Halim et al, 17 has considered the concentration of characterising and indicating ions as shown in Table 1