Idiopathic hypercalcinuria
A condition of excess urinary calcium with normal blood calcium.
Idiopathic hypercalciuria (IH) is a disorder marked by high levels of calcium in the urine while blood calcium stays normal, with no known cause. It is now the most frequent reason for hypercalciuria and the leading metabolic risk for kidney stones. IH can also lead to bone loss, such as osteopenia or osteoporosis, and affects the whole body because the system that keeps calcium balanced—in the intestines, blood, and bones—malfunctions. About 50 to 60 percent of people with kidney stones have IH, and they tend to have 5 to 15 percent less bone density than those without it.
There is no single agreed-upon definition for hypercalciuria. Hodkinson and Pyrah set the cutoff at more than 7.5 mmol of calcium per day for men and 6.25 mmol for women, but some think these limits are too strict because they ignore age, weight, and kidney function. Calcium excretion typically increases with age, especially after menopause in women, and does not follow a pattern of dropping and rising. Another suggestion is to define IH as excreting more than 4 mg of calcium per kilogram of body weight daily, which works better across different ages and sizes. IH looks a lot like hyperparathyroidism, but the key difference is that blood calcium stays normal in IH, while hyperparathyroidism typically presents with elevated blood calcium and abnormal parathyroid hormone levels.
Signs and symptoms often show up in children and involve the urinary tract. These include leaking urine, needing to pee often, bedwetting, kidney stones, urinary tract infections, blood in the urine, white blood cells in the urine without infection, small amounts of protein in the urine, pain when peeing, and ongoing belly pain.
Three main mechanisms are thought to cause IH: too much calcium absorbed from the gut, poor reabsorption of calcium in the kidney tubules, and too much calcium released from bones. Some researchers also think IH might come from too many vitamin D receptors or a lack of certain enzymes in the kidney tubules.
Regarding intestinal absorption, people with IH absorb calcium at twice the rate of healthy people and often have high levels of calcitriol. Calcium is absorbed mainly in the duodenum and less in the rest of the small intestine and colon, through both vitamin-dependent and vitamin-independent pathways.
- Field
- Medicine (metabolic disorders)
- Known for
- Most common cause of hypercalciuria and leading metabolic risk factor for nephrolithiasis
- Affects
- Entire body; particularly kidneys and bone density
- Prevalence
- 50%-60% of nephrolithiasis patients suffer from IH
- Bone density impact
- 5%-15% lower bone density in IH patients compared to those without
Lore & Background
Idiopathic hypercalcinuria arises due to faulty calcium homeostasis, a closely monitored process where slight deviations in calcium transport in the intestines, blood, and bone can lead to excessive calcium excretion, bone mineral density loss, or kidney stone formation. Three hypothesized mechanisms contribute: increased intestinal calcium absorption, faulty renal tubule calcium reabsorption, and increased bone resorption. Studies have found that IH patients have a rate of calcium absorption twice that of healthy individuals and elevated levels of calcitriol, though some patients show normal calcitriol levels, suggesting other factors are involved.
Reader's Guide
Idiopathic hypercalcinuria is significant as the most common cause of hypercalciuria and a major risk factor for nephrolithiasis, affecting 50%-60% of kidney stone patients. Its impact extends to bone health, with IH patients showing 5%-15% lower bone density. The condition's diagnosis involves differential diagnosis to exclude other causes and tests including 24-hour urine tests, blood tests, and imaging. Treatment considerations are complicated by the condition's heterogeneous pathogenesis, involving genetic factors with an autosomal dominant transmission pattern and environmental influences such as diet. The standard definition of hypercalciuria remains debated, with different criteria proposed by Hodkinson and Pyrah versus a weight-based definition.
Did You Know?
- IH shares many similarities with hyperparathyroidism; the only discernable feature between the two is the normal blood calcium level associated with IH.
- 43% of first-degree relatives and 36% of second-degree relatives of patients with hypercalciuria among nine families had IH.
- A study found that patients with IH have a rate of calcium absorption two times that of healthy individuals.
- IH has been considered a disorder affected by both environmental and genetic factors and has a heterogeneous pathogenesis.
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