IT HAS been said that 10 % of men and at least 5% of women will have at least one stone by the time they are 70 years old and these stones will commonly recur (Levine, Caring for the renal patient, 3rd Edition).
Patients and their doctors need to identify risk factors for the occurrence/recurrence of stones and work together to implement and monitor prevention strategies. These strategies include relevant modification of diet and/or medication.
The most common type of stone is the calcium oxalate stone which will be seen on X-ray (radiopaque) in contrast to uric acid stones which are radiolucent.
A patient with a renal stone may be asymptomatic. In this case, the stone is often detected because a routine medical examination indicated microscopic hematuria (blood in the urine, not obvious to the naked eye). The symptomatic patient usually presents because of pain (renal colic) which usually responds to analgesics (pain tablets). The patient may pass out the stone or the stone may be removed by less invasive methods currently available.
My approach to a patient with a "single stone episode" focuses on the history and the laboratory investigations as follows:
HISTORY
Enquiry about a family history of stones as this may suggest an inherited condition
(cystine stones are hereditary)
Enquiry about a low intake of fluid or an occupation that predisposes to increased loss as in excessive sweating. (Low urine output is a risk factor for calcium stones)
Enquiry about excess intake of dietary oxalate (found in fruits and nuts, green leafy vegetables)
Enquiry about high intake of salt, protein, calcium and vitamin D as these are factors which increase the risk for calcium stones
Enquiry about increase intake of purines (found in fish, meat and poultry) as an increase predisposes to uric acid and other purine stones.
Enquiry about past history of (i) hyperparathyroidism (increased activity of the parathyroid gland)
ii) sarcoidosis
iii) small bowel disease/surgery as these may predispose to calcium stones.
Enquiry about the intake of drugs e.g. excessive ascorbic acid which may cause increased oxalate in the urine
It is important to note that inappropriately restricting calcium intake may increase intestinal absorption of oxalate leading to an increase in formation of calcium oxalate stones (Curhan et al, 1993)
Examination: This is often
normal
LABORATORY TESTING
1. Assessment of kidney function by measurement of the levels of electrolytes, urea and creatinine in the blood
2. Measurement of the levels of uric acid, calcium and protein (albumin) present in the blood
3. Assessment for the presence of "cystine" in the urine (unless stone retrieved, analysed and cystine stone ruled out)
4. "Culture and microscopy of urine" to rule out infection .
5. Chemical analysis of the stone if possible
In patients who have recurrent stone formation it is advised that at least two 24 hour collections of urine be obtained to investigate the adequacy of urinary volume, urinary levels of sodium and urea (which reflect dietary intake of salt and protein), calcium, citrate, uric acid, oxalate, urine 'acidity' and "creatinine clearance" - a very good measure of kidney function.
This approach will reveal the level of kidney function and facilitate the identification of the causes for the formation of kidney stones. One can then embark on effective preventive treatment such as:
(i) removal of the parathyroid gland in a case of hyperparathyroidism (with increase in blood and urine calcium & stone formation)
(ii) modification of diet
(iii) discontinuation of implicated medication
In some cases, the cause of increased calcium and uric acid in the urine maybe 'idiopathic'- no identifiable cause. If dietary measures do not/cannot correct risk factors for kidney stone formation, different types of medication can be used for prophylaxis e.g. diuretics (to increase the volume of urine), alkali to change the 'acidity' of the urine (effective for dissolving uric acid stones and to a lesser extent cystine stones), allopurinol (for decreasing blood uric acid level) and chelating agents (used when there is much cystine in the urine). Struvite stones, produced in cases of chronic urinary infection, can be prevented
by long term antibacterial
treatment.
Dr. Yasmin Williams is
a family doctor and public
health specialist; email: yourhealth@gleanerjm.com.
Yasmin
Williams
HEALTH-WISE
