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Keywords:

  • urinary calculi;
  • risk factors;
  • magnesium;
  • Trinidad and Tobago

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Background characteristics
  7. Magnesium intake
  8. Discussion
  9. Acknowledgements
  10. References

objective  To identify risk factors for urinary tract stones in Trinidad and Tobago.

methods  A consecutive series of patients presenting to institutions in Trinidad for the management of proven urinary tract calculi was interviewed by questionnaires designed to obtain data on age, gender, ethnicity, occupation, stone location, a family history of stone disease, a past history of certain medical diseases and a semiquantitative estimate of the magnesium intake in food, ‘over the counter’ drugs and drinking water. An equivalent number of patients attending the same institutions for follow-up and verified from hospital records as having a previous radiological diagnosis of urinary tract stones, as well as a group of asymptomatic members of the community working in the same area, underwent the same interview. Chi-square, anova and Kruskal–Wallis tests were used to examine differences between the groups. Multiple logistic regression analysis was used to determine persistence of the significance of these differences after controlling for confounding variables.

results  Data sufficient for analysis were obtained for 122 previous and 102 prospective patients and 102 controls. The mean age of the patients was 32 years. The ratio of males to females was 0.9–1.8:1 for the affected groups, but significantly more males than females had calculi in the lower urinary tract (19%vs. 6%; P = 0.004). More patients (30%) than controls (7%) gave a positive family history of urinary tract stone disease (P < 0.001). Affected persons had a lower dietary magnesium intake (P = 0.003), which accounted for a significantly lower total magnesium intake (P = 0.02). Logistic regression analysis of the variables studied indicated that independent predictors of the disease were a positive family history (P = 0.001), total magnesium intake (P = 0.001) and age (P < 0.001).

conclusion  A low magnesium intake and a positive family history are highly predictive of urinary tract calculi in this population.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Background characteristics
  7. Magnesium intake
  8. Discussion
  9. Acknowledgements
  10. References

Urinary tract calculi are a universal source of renal pathology. Previous reports from the Caribbean give only indirect measures of the prevalence of this problem. These have indicated a need for surgical intervention in 71 patients over a 20-month period in Guyana (Sue Ling & Sharma 1980) and in 110 cases over a 5-year period in the Bahamas (Roberts & Bladimir 2000). These are countries with populations of 77 000 and 298 000 people, respectively, compared with a catchment population of 800 000 served by the institutions under review.

Currently available treatment will not dissolve most stones and modern ablative surgical approaches, while gradually becoming more refined, involve techniques and instruments of variable complexity and associated expense which are not always available in low-income countries. As a result, management of this condition, particularly in developing countries, is increasingly reliant on inhibiting stone growth and preventing the formation of new stones. Dietary variations are of particular interest in this regard, especially the frequency of intake of magnesium rich foods, such as avocados, beans and nuts, beets, citrus, coconut products, high fibre cereals, spinach and squash, and over the counter (OTC) medications like antacids, cough medicines, purgatives and vitamins.

Such a prophylactic approach requires the identification of factors which pre-dispose patients to urinary stones and these vary between populations. Therefore, studies undertaken to identify the circumstances that put particular populations at risk for stone formation continue to be of special relevance.

Risk factors consistent with this predilection include a mean age at diagnosis of less than 45 years and male gender in patients with lower tract stones, ethnicity, inherent genetic pre-disposition, previous medical conditions, the composition of the local water supply and the constitution of the diet (Ekane et al. 1997). The dietary intake of magnesium has generated particular interest because of the ability of this ion to exert a protective effect against urinary stone formation and growth (Angell & Resnick 1987).

In order to define which of these circumstances might be of particular importance in Trinidad and Tobago, a study was undertaken to investigate any significant difference in the expression of these variables in proven stone formers in our population, when compared with unaffected subjects. To the best of our knowledge there have been no previous structured attempts to determine possible epidemiological influences on urinary stone formation in these islands. The results herein reported may well be extrapolated to the Caribbean, or any tropical region with similar demographic features and dietary habits.

Materials and methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Background characteristics
  7. Magnesium intake
  8. Discussion
  9. Acknowledgements
  10. References

The study involved three groups. Group 1 consisted of a consecutive cohort of patients, referred for urological opinion, presenting, de novo, over a 1-year period, to the Port-of-Spain and Sangre Grande General Hospitals and to the private clinic of one of the authors (L.S.), for the treatment of proven urinary stone disease. Patients in group 2 were verified from hospital records to be previous radiologically confirmed stone formers. These were attending consecutively for follow-up at the same institutions. A control group of asymptomatic members of the community, in a similar age range, working in the same areas as those served by the institutions, formed group 3. This group was obtained by approaches to the customer service departments of companies operating in the same areas as the institutions, with an explanation of the intent and design of the study. Notices were posted inviting persons to come forward for interview by questionnaire. Potential recruits were required to confirm the absence of a history of any symptoms suggestive of urinary tract disease before coming forward. The number of potential responders excluded by this proviso could not be estimated.

All subjects were interviewed using a questionnaire designed to obtain data on age at diagnosis, gender, self-reported ethnicity, a family history of stone disease, the presence of a past medical history of hypertension, coronary heart disease, diabetes mellitus, or peptic ulcer disease, and an estimate of the oral intake of magnesium. Approval to conduct the study was granted by the ethics committees of the various hospitals and signed consent was obtained from all subjects prior to interview.

The magnesium intake was determined from the frequency of intake of a list of magnesium rich foods (containing >30 mg per serving) identified from the Ensminger Foods and Nutrition Encyclopedia (1989), and of OTC medication with a high magnesium content, as well as from the magnesium content of the water supply to the subjects' residences. A score was assigned to reflect the frequency of intake of the magnesium rich foods. The intake from OTC medications was deduced from the frequency of intake of a list of medications with a high magnesium content derived from Martindale's Extra Pharmacopoeia (1993). The subjects lived in different parts of the country. The water mineral content at each subject's residence was obtained from records compiled by the Water and Sewerage Authority of Trinidad and Tobago (1990–1994), the body responsible for the purification and distribution of water to the various areas of the country. Tests are conducted biannually by this Authority, during the wet and dry seasons, at 67 wells or reservoirs throughout the country. Study subjects were found to live in areas supplied by 35 of these, with access to water with a wide variation in mineral content.

The data were analysed using the SPSS program for Windows 9.0 (SPSS, Inc., Chicago, IL, USA). Chi-square tests were used to examine differences in categorical variables among the three groups of subjects. anova was used to examine group differences in age. Because of the skewed distribution of the data on mineral content, the Kruskal–Wallis test was used to examine group differences in mineral intake. Multiple logistic regression analysis was used to examine the significance of the differences between patients and controls after controlling for confounding variables. For this analysis, both patient groups were combined. The independent variables considered were: age, gender, ethnicity, occupation, family history, a past history of the medical conditions listed, the calcium and magnesium levels in the water supply, the relative magnesium intake in food and OTC medication and the total magnesium intake. P-values of <0.05 were considered statistically significant.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Background characteristics
  7. Magnesium intake
  8. Discussion
  9. Acknowledgements
  10. References

All control subjects who responded were confirmed to have never experienced symptoms of urinary tract disease and agreed to participate, as did all patients approached. Data sufficient for analysis were obtained from 122 previous and 102 prospective patients. The control group comprised 102 subjects.

Background characteristics

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Background characteristics
  7. Magnesium intake
  8. Discussion
  9. Acknowledgements
  10. References

The mean age of the patients in groups 1 and 2 was 29 and 34.5 years, respectively. The average age of the control group was 40.7 years (P = 0.01). Sixty-five per cent of the patients in group 1 were males, as were 47.5% of those in group 2 and 53.9% of controls. This difference was not significant (P = 0.07). Stones were present more frequently in East Indians (61%) than in Africans (20%) and those of mixed ethnicity (19%) (P = 0.001).

The left upper urinary tract (kidney, urethra) was affected more often than the right (92 vs. 58 = 41.2%vs. 26%). Both sides were involved in 42 patients (18.8%).The upper urinary tract was the more frequent site of calculi in both genders (192 vs. 30 patients = 86%vs. 14%). Significantly more males (19%) than females (6%) presented with calculi in the lower urinary tract (bladder, urethra) (P = 0.004). A few patients had stones at both levels. More patients (69; 31%) had a history of urinary tract stone disease in their immediate family than controls (seven; 7%). This difference was significant (P < 0. 001).

Enquiry was made regarding a past medical history of diabetes mellitus, hypertension, ischaemic heart disease and peptic ulcer disease. More patients than controls gave a history of ischaemic heart disease (P = 0.004). Diabetes mellitus (15.6%vs. 8%) and hypertension (21%vs. 13%) also occurred more frequently in the past medical histories of the combined groups of patients, but this difference failed to reach significance (P = 0.06 and 0.08, respectively). These characteristics are summarized in Table 1.

Table 1.  Characteristics of study populations and risk factors for urinary tract calculi
VariableProspective casesRetrospective casesControlsP-valueCombined casesOR* (95% CI)P-value
  • All numbers in columns are totals –n (%), unless stated otherwise.

  • *

     OR, odds ratio for ‘all cases’vs. controls.

n (%)122 (100)102 (100)102 (100) 224 (100)  
Mean age (±SD)29 (±13.5)34.5 (±13.8)40.7 (±10.1)0.00932.0 (±13.7)0.004
Age range (years)14–7520–7919–61 14–79  
Gender
 Male66 (65)58 (48)55 (54)0.07124 (55.4)0.94 (0.59–1.51)0.81
 Female36 (35)64 (52)47 (46) 100 (44.6)  
Ethnicity
 Indian76 (74)60 (50)27 (27)<0.001136 (61)5.0 (2.8–9.1)0.001
 African11 (11)33 (27)44 (43) 44 (20)  
 Mixed15 (15)28 (23)28 (28) 43 (19)  
 Others003 (2) 0  
Family history
 Positive45 (48)24 (22)7 (7)<0.00169 (30.8)1.97 (1.46–2.66)<0.001
Past medical history
 Diabetes18 (18)17 (14)8 (8)0.1135 (15.6)2.18 (0.97–4.88)0.06
 Hypertension22 (23)25 (23)13 (13)0.2147 (20.9)0.56 (0.29–1.08)0.08
 Ischaemic heart disease11 (11)21 (17)2 (2)0.00132 (14.3)8.33 (1.96–35.4)0.004
 Peptic ulcer disease9 (9)11 (9)5 (5)0.4520 (8.9)1.90 (0.69–5.22)0.21

Magnesium intake

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Background characteristics
  7. Magnesium intake
  8. Discussion
  9. Acknowledgements
  10. References

We considered the water supply to the place of residence to be a consistent source of mineral intake. There was no significant difference in the individual calcium and magnesium content of the water used by patients and controls (P = 0.39 and 0.6, respectively). However, the ratio of calcium:magnesium in the water consumed by patients and controls differed significantly (P = 0.03). Unaffected subjects had a significantly higher food and total magnesium intake than either of the two patient groups (P = 0.003 and 0.02, respectively). There was no difference in the intake of magnesium in OTC medication between the groups (P = 0.80). These data are set out in detail in Table 2.

Table 2.  Summary of mineral intake of patients compared with normals
VariablesProspective casesRetrospective casesControlsP-valueCombined casesP-value
  • All numbers in columns are median values in mg/dl; ranges are in parentheses.

Water Ca32 (4.4–95.8)*46.8 (5.5–95.8)40.6 (7.3–108.6)0.00443.0 (4.4–95.8)0.39
Water Mg7 (3.5–11.9)7.4 (4.1–11.9)7.2 (4.3–18.1)0.227.0 (3.5–11.9)0.60
Water Ca:Mg4.6 (1.3–11.9)5.8 (0.8–11.9)4.8 (1.7–15)0.014.9 (0.8–11.9)0.03
OTC Mg0.7 (0–20)0.7 (0–20.4)1.1 (0–20)0.800.72 (0–20.4)0.55
Food Mg28.4 (2.2–60.8)27.2 (3.7–77.9)33.3 (7.2–91.5)0.00327.7 (2.2–77.9)0.001
Total Mg41 (8.9–73.5)38.4 (9.6–106.6)44.9 (12.5–102.1)0.0239.0 (8.9–106.6)0.01

Multiple regression analysis indicated that, after controlling for potential confounding variables, the differences in dietary and total magnesium intake retained statistical significance (P = 0.001). A positive family history and age were also significant predictors of disease (P = 0.001 and <0.001, respectively).

Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Background characteristics
  7. Magnesium intake
  8. Discussion
  9. Acknowledgements
  10. References

Several epidemiological factors have been implicated in a pre-disposition to urinary stone disease. These include age (Kodama & Ohno 1989; Joual et al. 1997; Kim et al. 1998), gender (Kodama & Ohno 1989; Baker et al. 1993; Joual et al. 1997), ethnicity (Kodama & Ohno 1989), past medical history (Robertson et al. 1983), social class and profession (Iguchi et al. 1996), nutritional factors and inherent genetic pre-disposition (Ljunghall 1979; Ekane et al. 1997). This study attempted to determine whether these epidemiological influences were associated with stone formation in Trinidad and Tobago.

The mean age at diagnosis of our patients was 32 years, which is somewhat lower than averages of 40–45 years reported from Ghana by Klufio et al. (1996), from Taiwan by Yanagawa et al. (1997), from France by Joual et al. (1997) and from the USA by Sowers et al. (1998). There was a male:female ratio of 0.9–1.8:1 in our patients, compared with previous Taiwanese and Ghanaian studies, which found a male to female ratio of 2–2.4:1 (Klufio et al. 1996; Yanagawa 1997). Our male subjects did have a higher frequency of lower urinary stones than females, a difference previously noted in other developing countries and ascribed to the influence of concomitant urinary tract infection (Kodama & Ohno 1989).

Earlier reports suggested that blacks suffer from urinary stone formation less frequently than whites (Kodama & Ohno 1989; Krieger et al. 1996). Even though there is an equal distribution of people of African and East Indian extraction in the population of Trinidad and Tobago (40% each), this study found a lower rate in Africans than East Indians. This may be caused by dietary differences, but our patients and controls were not matched for ethnic composition, devaluing any such surmise.

A suggestion that there is a significant incidence of urinary stones in patients with hypertension (Robertson et al. 1983; Borghi et al. 1999) has not been validated by all observers (e.g. Sowers et al. 1998). This study found a higher incidence of ischaemic heart disease in patients than controls (P = 0.004). However, differences in the occurrence of a past medical history of diabetes mellitus and/or hypertension between patients and controls failed to achieve significance (P = 0.06 and 0.08, respectively), although both of these conditions are known to pre-dispose to coronary artery disease.

A pre-ponderance of the sedentary, affluent and administrative classes among affected persons has been described in previous studies (Kodama & Ohno 1989; Iguchi et al. 1996). Ignorance about the rate of the disease in each of the occupational categories we identified, as well as possible bias in the selection of the controls, precluded meaningful analysis of our occupational data.

Magnesium, by its ability to increase the solubility of calcium oxalate, has been shown to decrease the incidence of stone formation, as well as prevent stone growth (Angel & Resnick 1987). We compared the level of magnesium intake, in food, water and OTC medications, of patients relative to unaffected subjects. Magnesium rich foods selected for investigation of frequency of intake included avocados, beans and nuts, citrus fruits and juices, cocoa and coconut products, corn, whole wheat and oat cereals, and certain vegetables such as beets, spinach and squash. OTC medications were mainly antacids, cough and cold medications, purgatives and vitamins. The water supply to the place of residence, rather than the work-place, was considered to be a consistent source of mineral intake. These attempts at quantifying the relative intake of magnesium in water, food and OTC medication by stone formers compared with a series of unaffected persons have suggested an advantage for a relatively high intake of magnesium in food.

A higher frequency of stones among the relatives of stone formers than in relatives of unaffected subjects has been pointed out by observers from Scandinavia (Ljunghall & Hedstrand 1975; Ljunghall 1979), the UK (Robertson et al. 1983), Italy (Trinchieri et al. 1988), Japan (Ishikawa et al. 1995), Kuwait (El-Reshaid et al. 1997) the USA (Curhan et al. 1997) and Korea (Kim et al. 1998). Trinchieri et al. (1988) found that the corresponding relatives of the spouses involved were less affected, supporting a genetic pre-disposition, in contradiction to Ljunghall (1979) who had earlier described a parallel increased tendency to stone formation among the wives of those whose relatives had stones. Our data support the general predictive value of a positive family history for affected Trinidadian subjects.

There are obvious difficulties in separating out the role of shared familial exposure to food and water during the formative years from purely genetic influences. Such a dissection might require a comparative analysis of the incidence of the disease between first degree relatives of affected people and relatives of their spouses, as was carried out by Ljunghall (1979) and Trinchieri et al. (1988), with conflicting conclusions. An assessment of the influence of the water supply is also challenged by variations in volumes drunk both at home and at the work-place. Future studies may require a limitation of study subjects to those based at home, perhaps exposed to water with established differences in mineral content. An alternative approach was adopted by Rodgers (1998), who used an interventional cross-over design to compare the influence of water with variable mineral content on patients and controls. The results suggested that the consumption of mineral water rich in calcium and magnesium favourably altered risk factors for urinary calcification. Our study relied on a comparison of the quality of water available at the place of residence, the relative intake of which would have varied among those being studied.

The study suffered from several other limitations. Recruitment bias existed for both study patients and controls. Closer matching of the control group, for age, race and occupation, with the patients would have allowed more validity to be ascribed to the influence of a positive family history and the mineral intake in food, water and medication. A recall bias also existed for past patients and unaffected subjects, as currently affected patients would be more likely to have enquired about, and be familiar with, a family history of urinary tract calculi. As well as this, the magnesium intake in food only focused on the consumption of magnesium rich foods, because the questionnaire could not include all foods that contain magnesium. The questionnaire was also not validated. Eventual sample sizes were determined by limitations on resources and logistics, rather than a calculation of the number of subjects required to detect anticipated differences.

Nevertheless, the results of this study confirm the significance of a positive family history of stone disease in close relatives in this population and suggest a protective role for a high magnesium intake. This offers support to the theory that an inherent genetic pre-disposition to urinary stones may be expressed after a variable period of inappropriate mineral intake.

Despite the reservations discussed, emergent trends suggest some guidelines for patient counselling to prevent or delay stone formation. It would appear to be indicated, in addition to offering the usual advice given to potential or actual stone formers on a liberal fluid intake (Borghi et al. 1999), to educate the public on the identification, and consumption of, locally available magnesium rich foods. There is also a need to proactively screen the first-degree relatives of affected stone formers and, perhaps, hypertensive patients. The fact that stone formation and growth must precede disease onset and presentation, which occasionally occurs during late childhood, supports the view that such screening should be offered from the early adult years.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Background characteristics
  7. Magnesium intake
  8. Discussion
  9. Acknowledgements
  10. References

The interviews and data entry were carried out by Ms Rhonda Hassanally, who was employed as a research assistant by the University of the West Indies for the duration of the study. This project was funded by a Research and Publication grant from the University of the West Indies, St Augustine Campus.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Background characteristics
  7. Magnesium intake
  8. Discussion
  9. Acknowledgements
  10. References
  • Angell AH, & Resnick MI (1987) Urinary inhibitors and promoters of stone formation. In: Stone Disease. Diagnosis and Management (ed. SRous) Harcourt Brace Jovanovitch, New York, pp. 1940 .
  • Baker PW, Coyle P, Bais R & Rofe AM (1993) Influence of season, age, and sex on renal stone formation in South Australia. Medical Journal of Australia 159, 390392.
  • Borghi L, Meschi T, Schianchi T et al. (1999) Urine volume: stone risk factor and preventive measures. Nephron 81 (Suppl. 1), 3137.
  • Curhan GC, Willett WC, Rimm EB & Stampfer MJ (1997) Family history and risk of renal stones. Journal of the American Society of Nephrology 8, 15681573.
  • Ekane S, Wildschutz T, Simon J & Schulman CC (1997) Urinary lithiasis: epidemiology and physio-pathology (Review). Acta Urologica Belgica 65, 18.
  • El-Reshaid K, Mughal H & Kapoor M (1997) Epidemiological profile, mineral metabolic pattern and crystallographic analysis of urolithiasis in Kuwait. European Journal of Epidemiology 13, 229234.
  • Ensminger Foods and Nutrition Encyclopedia (1989). Pegus Press, Clovis, pp. 802989.
  • Iguchi M, Umekawa T, Katoh Y, Kohri K & Kurita T (1996) Prevalence of urolithiasis in Kaizuka City, Japan – an epidemiologic study of urinary stones. International Journal of Urology 3, 175179.
  • Ishikawa Y, Konya E, Yamate T et al. (1995) Influence of genetic factors on family history of upper urinary stones. Hinyokika Kiyo 41, 349353.
  • Joual A, Rais H, Rabii R, El Mrini M & Benjelloun S (1997) Epidemiology of urinary lithiasis. Annals of Urology (Paris) 31, 8083.
  • Kim SC, Moon YT, Hong YP et al. (1998) Prevalence and risk factors of urinary stones in Koreans. Journal of Korean Medical Scences 13, 138146.
  • Klufio GO, Bentsi IK, Yeboah ED & Quartey JK (1996) Upper urinary stones in Accra, Ghana. West African Journal of Medicine 15, 173176.
  • Kodama H & Ohno Y (1989) Descriptive epidemiology of urolithiasis. Hinyokika Kiyo 35, 923934.
  • Krieger JN, Kronmal RA, Coxon V, Wortley P, Thompson L & Sherrard DJ (1996) Dietary and behavioral risk factors for urolithiasis: potential implications for prevention. American Journal of Kidney Diseases 28, 195201.
  • Ljunghall S (1979) Family history of renal stones in a population study of stone-formers and healthy subjects. British Journal of Urology 51, 249252.
  • Ljunghall S & Hedstrand H (1975) Epidemiology of renal stones in a middle-aged male population. Acta Medica Scandanavia 197, 439445.
  • Martindale's Extra Pharmacopoeia (1993), 30th edn (ed. JEFReynolds) The Pharmaceutical Press, London, pp. 10321629.
  • Roberts R & Bladimir A (2000) Transurethral ureteroscopy for upper urinary tract stone in Bahamas: a five-year experience 1993–98. West Indian Medical Journal 49 (Suppl. 2), 50.
  • Robertson WG, Peacock M, Baker M & Marshall DH (1983) Studies on the prevalence and epidemiology of urinary stone disease in men in Leeds. British Journal of Urology 55, 595598.
  • Rodgers AL (1998) The influence of South African mineral water on reduction of risk of calcium oxalate kidney stone formation. South African Medical Journal 88, 448451.
  • Sowers MR, Jannausch M, Wood C, Poe SK, Lachance LL & Peterson B (1998) Prevalence of renal stones in a population-based study with dietary calcium, oxalate, and medication exposures. American Journal of Epidemiology 147, 914920.
  • Sue Ling H & Sharma D (1980) The surgical management of urinary tract calculi. West Indian Medical Journal 29, 288.
  • Trinchieri A, Mandressi A, Luongo P, Coppi F & Pisani E (1988) Familial aggregration of renal calcium stone disease. Journal of Urology 139, 478481.
  • Water and Sewerage Authority of Trinidad and Tobago (199094) Statistical Analysis of Water Sources. Quality Control Department.
  • Yanagawa M, Kawamura J, Onishi T et al. (1997) Incidence of urolithiasis in northeast Thailand. International Journal of Urology 4, 537540.

Authors DrTrevor Anatol, Department of Clinical Surgical Sciences, Faculty of Medical Sciences, University of the West Indies, St Augustine, Trinidad and Tobago. Tel.: +868 645 2640 (extn. 3917); Fax: +868 663 4319; E-mail: surgsci@tstt.net.tt (corresponding author). Dr Lexley Pinto Pereira, Department of Paraclinical Sciences, Faculty of Medical Sciences, University of the West Indies, St Augustine Campus, Trinidad and Tobago. Tel.: +868 645 2640 (extn. 4605); Fax: +868 663 8613; E-mail: lexleyp@hotmail.com Dr Donald Simeon, Department of Paraclinical Sciences, Faculty of Medical Sciences, University of the West Indies, St Augustine, Trinidad and Tobago. E-mail: dtsimeon@tstt.net.tt Dr Lall Sawh, Consultant Urologist, General Hospital, Port of Spain, Trinidad and Tobago. Tel.: + 868 625 7294; Fax: + 868 623 7294; E-mail: lrsawh@tstt.net.tt