Recently, there are groups of infants and children with urinary stones in several provinces and cities in China, which are caused by melamine-contaminated milk powder. What is melamine? How can it be found in milk powder for infants and children? What kind of damage can it cause to the affected children? How is it diagnosed and treated? What is melamine? Melamine is a nitrogen heterocyclic organic compound produced from urea, which is a white monoclinic crystal at room temperature and has no significant odor. It is mainly used in the production of wood processing, plastics, paints, paper, adhesives, textiles, leather, electrical appliances, pharmaceuticals, flame retardants, etc. Due to the low cost of domestic urea production, China is currently the country with the largest variety of melamine production technology in the world and the world’s largest melamine production base and exporter. How can melamine appear in milk powder consumed by infants and children? Since mid-March 2007, there have been more than 4,000 deaths from poisoning of cats, dogs and other pets in the United States. In its investigation, the U.S. Food and Drug Administration (FDA) found that the chemical melamine was contained in wheat protein powder and rice protein powder, the main ingredients of several well-known brands of pet feed. Can melamine be added to food and feed? It has not previously been specifically proven by the relevant authorities. In China, melamine is not listed as a feed additive, but there are no laws or regulations that explicitly prohibit it. In the U.S., the FDA has also not previously had specific regulations for the substance. Does the legal gap leave any room for it? One of the most important indicators for evaluating the quality of animal feed is its protein content. As people often use “nitrogen content to presume protein content”, adding melamine to animal feed can increase the nitrogen content of the feed and make people believe that the feed is rich in protein content, thus improving the competitiveness of the product. Although no final explanation has been given as to why melamine may be harmful in the country, I venture to speculate that the possibility of adding melamine to milk powder production to increase the “nitrogen content” of the food cannot be ruled out at this time. What kind of damage can melamine do to a child? The U.S. FDA investigation into the March 2007 pet poisoning deaths has conclusively confirmed that the culprit was melamine contained in wheat protein flour and rice protein concentrate. The danger of this substance to humans and animals is not yet fully understood, and the consensus conclusion is that “kidney damage may occur with prolonged and repeated exposure to the substance”. While people are worried about the secondary hazards that may arise when people consume animal products exposed to melamine, the hazards of melamine-containing milk powder consumed directly by some infants and children in China are already in front of us. Toxicological experiments on animals showed that acute toxicity experiments were conducted by gavage of mice with melamine, and a large number of crystals accumulated in the ureters of mice that died by gavage, and some of the mice had crystals covering the kidney peritoneum. In the sub-chronic toxicity test, lymphocyte infiltration was observed in the kidney and crystals were found in the tubular lumen of the kidney, while the biochemical indexes showed a gradual increase in serum urea nitrogen (BUN) and creatinine (CRE). Based on previous animal toxicology experiments and the current clinical manifestations of infants and children who ingested melamine-contaminated milk powder, it is possible that melamine caused multiple urinary stones in children. There is no direct evidence of damage to other tissue systems caused by melamine. How to make diagnosis and treatment? Clinical manifestations (a) unexplained crying, especially during urination, may be accompanied by vomiting; (b) visual or microscopic hematuria; (c) acute obstructive renal failure, manifested as oliguria or anuria; (d) stones may be excreted in the urine, such as male infants with stones obstructing the urethra may manifest as painful urination and difficulty in urination; (e) hypertension, edema, and percussion pain in the kidney area may be present. Diagnostic points (a) History of infant formula feeding with Sanlu brand. (B) One or more of the above clinical manifestations. (C) Laboratory tests: routine urine (visual or microscopic hematuria), blood biochemistry, liver and kidney function, urinary calcium/urinary creatinine (generally normal), urinary red blood cell morphology (non-glomerular-derived hematuria), parathyroid hormone measurement (generally normal). (iv) Imaging: Urological ultrasound is preferred. If necessary, CT scan of the abdomen and intravenous urography (contraindicated in the absence of urine or renal failure), and renal nuclide scan is feasible to evaluate fractional renal function. Ultrasound features of urinary stones in infants and young children caused by the consumption of contaminated Sanlu infant formula: general features: enlargement of both kidneys; parenchymal echogenicity enhancement, parenchyma mostly of normal thickness; mild dilatation of renal pelvis and calyces, rounding of renal calyces; if the obstruction is located in the ureteral lumen, the ureter is dilated above the point of obstruction; in some cases, perinephric fat pad and soft tissue edema around the ureter; as the disease progresses, the renal pelvic wall and In some cases, the perinephric fat pad and soft tissues around the ureter are edematous. The majority of stones involve the bilateral collecting system and bilateral ureters; ureteral stones are mostly located at the pelvic-ureteral junction, ureter across the iliac artery and ureteral-vesical junction; stones are crumb-like accumulation, involving a large area, with a faint posterior acoustic shadow, most of them are different from calcium oxalate stones, and the posterior edge of stones can be detected; urinary tract obstruction due to stones is more complete. Differential diagnosis (a) Differentiation of hematuria: pay attention to exclude glomerular-derived hematuria. (B) Differentiation of stones: stones are usually X-ray negative stones, which are not visible on urinary X-ray, and can be differentiated from positive stones such as calcium oxalate and phosphate, which are not X-ray positive. (C) Differentiation of acute renal failure, paying attention to the exclusion of prerenal and renal renal failure. Treatment (a) Immediately stop using Sanlu brand infant formula. (B) Conservative medical treatment: rehydration, alkalinization of urine to promote the discharge of stones; correction of water, electrolytes and acid-base balance disorders. During the course of conservative treatment, urinary routine, blood biochemistry, renal function should be closely checked, and ultrasound should be repeated (especially pay attention to the degree of dilatation of renal pelvis and ureter and changes in stone shape and location). As the stones are loose or sand-like, they are more likely to be expelled on their own. (iii) Treatment of combined acute renal failure: Firstly, life-threatening conditions such as hyperkalemia should be corrected, such as the application of sodium bicarbonate and insulin, and if conditions are available, blood purification, peritoneal dialysis and other methods should be taken as early as possible, and if necessary, surgical intervention to relieve stone obstruction. (iv) Surgical treatment: If the stone morphology and location do not change by conservative medical treatment, and the hydronephrosis and renal damage are aggravated, or if renal failure does not allow hemodialysis or peritoneal dialysis, the obstruction can be removed surgically. Cystoscopic retrograde ureteral cannula drainage, percutaneous nephrostomy drainage, surgical excision and stone extraction, percutaneous nephrolithotomy, etc. are available. Because the stones are loose, uric acid is the main component, and the patient is an infant, extracorporeal shock wave lithotripsy has greater limitations and needs to be considered carefully. After the treatment, the stone obstruction is released, the general condition is improved, the kidney function is normalized, and the urine can be discharged. Follow-up after discharge: urinary routine; urological ultrasound; renal function test; intravenous pyelogram if necessary.