A few general words about kidney stones
I suppose anyone who produces kidney stones knows they are hard and unwanted objects made in the kidney that cause pain, bleeding, and obstruction of the urinary tract, and lead to urinary infections and surgery. Most patients come to realize that stones recur, because over half of those who have formed only one stone will form another within 5 – 10 years. Many patients have seen the stones they form, black, or orange, or yellow, or gray, smooth or spiky, surprisingly small for all the trouble they cause, or surprisingly large to think it really passed through the urinary tract. All patients who have formed stones, at least all the ones I have ever met, want to prevent more.
Stones are hard because they are made of crystals
The history and modernity of stone disease lies in this simple phrase. Stones are hard and troublesome precisely because they are made out of crystals, and crystals make stones hard because they are themselves tiny solid particles that can pack tightly together to make the stones. It is true that crystals are bound up with organic molecules and that the key to future progress in stone prevention may be ultimately found within the complex chemistry of these organic molecules. But for the moment they are irrelevant to patients and their physicians. Only rarely do the organic molecules themselves make ‘soft’ stones. It takes crystals to make stones so hard and therefore so troublesome as they are. And it is to prevent crystals from forming and growing that we search out in our patients the causes of their crystals and thereby the means for their prevention.
I think people have always believed that high fluid intake will reduce stone formation, although a detailed review of the literature has concluded that of all those published only one trial supports that belief and is well enough designed that it has credence. This figure from that one trial shows that formation of a new stone was delayed by high water intake in patients who had formed a single stone. After just one stone nearly 30% of people who did not increase their urine volume (Group 2, average 1 liter daily) had formed at least one more by 5 years whereas only 10% of those with a higher fluid intake (Group 2, 2.6 liters daily) did so. But it is hard to do everything with just fluids. The day is long and various. There is nighttime. People forget. Crystals never sleep. Crystals never forget. It may be true that in a trial, with prompting from nurses, people will maintain a high urine flow, but how about the usual situation? You want fluids. But you also want whatever treatment aims most precisely at the crystals you form. That means you need to know what those crystals are. And to find out what the crystals are the stones must be analysed.
Crystal specific treatment is far better than general measures for patients with more than one calcium stone
The patients in the water trial had formed only one stone each, so far as could be told, and only 25% of those who did not raise their urine volumes (Group 2) had another stone in five years. Among people who have formed at least several stones, 60% in the control groups of trials that tested specific treatments formed at least one more stone within 3 years, whereas only 15 – 20% of those receiving specific treatments formed another stone during the same interval. High water intake may well be ideal for those who have formed only one stone, but the large numbers of patients who have formed more than one stone will predictably form more stones at much higher rates and benefit greatly from treatments that focus on their specific stone crystal.
Stones are not always made of calcium crystals
Even though I showed the one water trial as an example of a general measure, the patients formed calcium stones, and so the trial applies only to them. But stones are commonly made of other than calcium crystals. I will detail this in another post, but note here that uric acid, cystine, and struvite are found often enough to matter. Some drugs form crystals. Calcium stones can contain uric acid, or struvite, or even cystine. Uric acid, struvite, and cystine crystals have special treatments, and water alone is not acceptable. Even among calcium stones, experts have their quibbles about the best treatment approaches, so just being ‘calcium’ is not enough of a description for stones. Calcium stones can be calcium combined with oxalate, the so called common calcium oxalate stone. They can be calcium combined with phosphate, so called hydroxyapatite or brushite stones depending upon the exact crystal type found. Water is not usually enough for prevention of calcium phosphate stones. Mixtures of the calcium crystals are very common and this fact can affect treatment.
Stones are analysed by special laboratories
Stone analysis is performed by specialized laboratories, and is not overly expensive. One company has posted its prices. If you send the stone and pre-pay it is $40.00 with 2 photographs of the stone. Your doctor can get it for $35.00. This is only one of many companies that sell the service. The report from any stone analysis laboratory is usually a single page that lists each type of crystal found in the stone and a rough approximation of the percentage of the stone each crystal accounts for. The stones are powdered for the analysis. If you send a batch of stones, it will be cheap per stone but the powdering of the batch will mix everything together so you get an average. If all the stones are passed at one time, I would opt for a batch. If they were passed at different times, I would do them individually because things change.
Stone analysis is the prime and fundamental basis of stone prevention.
Whether you send them, or your doctor does, and whether you pay by the stone or the batch the analysis is important. It is the stone crystals we want to prevent. Your doctor needs to know what they are. You need to know, too.
Fred Coe MD