Epidemiology of primary hypercalciuria

Introduction

Hypercalciuria is a biochemical syndrome consisting of an ex­aggerated urinary excretion of calcium exceeding the upper “normal” limits. cialis professional cheap canadian drugs

Several definite diseases may account for hypercalciuria such as hyperparathyroidism, sarcoidosis, malignant neoplasm, im­mobilization, vitamin D excess, lithium, etc. Hypercalciuria without clinical cause is defined as idiopathic hypercalciuria. It was originally described in male stone form­ers but also occurs in women with kidney stones and, at a much lower frequency, in otherwise normal people. The figure of prevalence of hypercalciuria in the population varies according to its definition and to some factors such as age, gender, race and diet.

Definition

Urinary excretion of calcium is usually expressed in mg/24 hour. Commonly accepted daily upper normal limits for calcium excretion are 300 mg for men and 250 mg for women. They derive from a large study by Hodgkinson and Pyrah, who found that calcium excretion exceeded these limits in more than 30% of male and female stone formers, but in less than 5% of otherwise normal people. However these limits are arbi­trary and the choice of the value that best separates abnormal from normal urinary calcium output is difficult owing to the wide range of mean urinary calcium excretion values observed in different series. Hodgkinson and Pyrah observed in Leeds a mean calcium excretion of 178 mg/day by normal men and 140 mg/day by normal women. A subsequent survey, 12 years lat­er, revealed values of urinary calcium output in normal male and female subjects appreciably higher of 219 and 186 mg/day, respectively. Similarly, different mean values for uri­nary calcium excretion were reported from different geographi­cal areas and in different periods of time. These differences can be explained by differences in the selection of the popula­tion examined, in the modality of collection of urinary samples, in the laboratory methods, and in the changes of dietary habits over the years or related to the geographical area (Table I). Other confounding factors are related to possible variations of the urinary calcium excretion during the day and between dif­ferent days, because hypercalciuria is frequently intermittent presumably because of dietary variations. Some evaluation protocols involve multiple collections of 24 hour samples or separate sample collections for working days and week-ends. On the other hand the collection of samples under defined or restricted dietary conditions could introduce biases difficult to define, so the preferred approach should be to study subjects ingesting their customary diets, by collecting urine on out-pa­tient basis together with a brief dietary history. Another bias re­lated to the evaluation of daily calcium output is an incomplete collection of the urines. This implies that urinary volume should be controlled through the values of creatinine excretion. Nordin suggested to employ the urinary calcium to urinary creatinine ratio in order to express urinary calcium excretion in both ran­dom and 24 hour collections. Hypercalciuria is consequently defined by more than 0.15 mg calcium for mg of urinary creati­nine in a 24-hour collection. The calcium/creatinine ratio of ran­dom samples allows the evaluation of calcium excretion under different physiological (i.e. fasting, after meals) and experimen­tal (i.e. calcium load, acid load) conditions. In order to minimize the effects of glomerular filtration rate on calcium excretion, calcium output can be also expressed as mg/100 ml of glomerular filtrate. The calcium/body weight ratio is an effective alternative to daily urinary output, especially for nutritional stud­ies and for assessment of urinary calcium in children. Com­monly the accepted upper limit is of 4 mg/kg body weight/24 hour, for both sexes.

Table I – Daily urinary calcium (mg/24 hour) in healthy subjects and calcium renal stone formers (RSF) from different geographical areas.

Healthy subjects

Calcium RSF

Dietary intake

South Africa (blacks) (3)

51±33

146±80

North-West India (4)

99±24

128±32

Bulgaria (5)

125±56

171±104

Brazil (6)

149±77

245±133

468
543

South Africa (whites) (3)

161±69

233±108

Australia (7)

164
(median)

188
(median)

Italy (8)

202±93

296±125

Italy (9)

178±86

234±120

956
1148

U.K. (1958) (1)

178
(males)

140
(females)

260
(males) 186 (females)

800

U.K. (1970) (2)

219±10
(males) 186±7 (females)

338±10
(males) 241±11 (females)

1000

U.K. (1978) (10)

238±15

320±14