How to keep away the ‘silent stone former’
Calcium oxalate predominates amongst calculogenic chemicals that go to make renal stones. Calcium oxalate is the calcium salt of oxalic acid. Calcium oxalate in urine is usually referred to as ‘oxalate’.
Urinary calcium oxalate crystals when magnified (under a microscope) appear in shape as a pyramid/envelope or dumbbell. Usually, normal urine does not contain these (microscopically visible) oxalate crystals. Occasionally, a few such crystals may be seen randomly. However, a ‘likely renal stone former’ or a ‘sufferer of renal stone disease’ would show these types of crystals in the urine.
Whether one is a ‘likely renal stone former’ or a ‘sufferer of renal stone disease’ cannot be ascertained simply by the mere presence of microscopically visible calcium oxalate crystals. The ‘Urine Lithogenic Test’ is the definitive medical laboratory test to detect ‘proneness’ to urolithiasis, and identify the ‘silent stone former’. Further the ‘Urine Lithogenic Test’ can be employed to detect the success or failure of therapy and also non-compliance to therapy.
How to avert Calcium oxalate renal stone formation:
Calcium oxalate is nearly insoluble in the urine.
Calcium oxalate presence in the urine in high concentrations persistently predisposes to Calcium oxalate renal stone formation.
Calcium oxalate, not being an essential substance is removed from the body via urine.
Dietary oxalate is found in high concentration in certain vegetables, fruits and nuts.
Some amount of Oxalate found in the urine is, what is partly absorbed from the diet. And, absorption of dietary (soluble) oxalate can be minimised, relieving oxalate load in the urine.
Some amount of Oxalate excreted in the urine is formed (synthesised) within the body.
Calcium oxalate being almost insoluble in urine, calls for urine dilution as the first and prime remedial measure to keep it at a very low concentration in the urine, thereby preventing new stone formation or hindering the growth of stone already formed. This can be achieved by drinking sufficient amounts of water to keep the urine diluted or in other words, prevent urine getting concentrated.
The water intake (unless indicated otherwise) must be such that one passes a minimum of two litres (2L) of urine per day. The water intake must compensate for water loss via sweat, particularly when engaged in heavy physical labour, strenuous exercise and when suffering from fever. Dilution of urine is the first and foremost preventive measure opposing oxalate renal stone disease.
The second approach is to minimise the amount of Calcium oxalate entering into the urine from exogenous sources (i.e. from outside sources of food).
Calcium oxalate, being a nutritionally non-essential substance, is eliminated from the body via urine without use. The second most important preventive strategy is to skip altogether/ strictly cut down oxalate containing food articles. This partly ensures that the urine is not saturated with stone-forming Calcium oxalate originating from the diet.
Dietary oxalate is an organic ion found in certain vegetables, fruits and nuts.
It must be borne in mind that oxalate is present only in foods of plant origin. It is important for all ‘likely stone formers’ and ‘those who are harboring growing renal stones’ to know these food substances, to avoid or severely curtail their intake.
Absorption of dietary soluble oxalates (such as Potassium oxalate, Magnesium oxalate) can be minimised by conversion to unabsorbed insoluble Calcium oxalate within the gut to lower the renal oxalate load.The amount of dietary soluble oxalate being absorbed from the gut can be reduced by promoting oxalate excretion in the faeces as Calcium oxalate. In this way, the quantity of oxalate of dietary origin, entering into the body and reaching the urine can be lowered, thereby lowering the urinary Calcium oxalate concentration. Conversion of Potassium oxalate/Magnesium oxalate to insoluble Calcium oxalate within the gut promotes oxalate elimination in the faeces, lowering oxalate absorption into the body.
Experiments in humans have shown that incorporating whole milk, low-fat milk, curd (rich in Calcium) into the meal had proven successful in lowering the absorption of dietary soluble oxalates in the gut. One may be nonplussed: ‘Why increase Calcium (Ca++) in the diet, which is a component of renal Calcium oxalate stones (whose formation has to be stalled)?’ One has to understand that a surfeit of Calcium in the diet will convert absorbable dietary soluble oxalate to insoluble Calcium oxalate which will be excreted with the faeces.
Human Biochemistry reveals that a certain amount of Oxalate excreted in the urine is formed naturally within the body (endogenous synthesis). One of the chemical compounds that goes to form oxalate within the body is Vitamin C (ascorbic acid). It had been shown experimentally, thatVitamin C ingested over and above the recommended daily requirement (RDA) is converted to Oxalic Acid within the liver. As this oxalic acid is unrequired (an antimetabolite), it is directed to kidneys for excretion. Thus the urine oxalate load augments. Therefore, stone formers and likely stone formers must take steps to minimise surfeit oxalate production within the body by limiting supplementary Vitamin-C ingestion.
Thus water intake to ensure sufficient urine output (b) restriction of dietary oxalate and increasing Calcium content of meals to minimise Calcium oxalate buildup in the urine had been proven successful in minimising / averting Calcium oxalate urolithiasis.
Urinary uric acid is a normal excretory substance present in the urine. Elevated urinary uric acid in the urine may provide additional nucleation centres for deposition of Calcium oxalate crystals leading to Calcium oxalate renal stone formation. However, formation of uric acid within the body can be minimised by reducing / avoiding dietary intake of animal meats. Refrain from eating red meats and take proteinaceous plant foods to meet the daily protein requirement.
(The writer is a retired lecturer in Clinical Biochemistry and Nutrition)