The Measurement of Intestinal Calcium Absorption by External Radioisotope Counting: Application to Study of Nephrolithiasis

Abstract

1. Gastro-intestinal absorption of calcium was studied in man by the measurement of forearm radioactivity in a large-volume liquid scintillation counter following separate oral and intravenous doses of 47CaCl2. From the ratio of the percentages of total radioactivity appearing in the forearm following these separate determinations the fractional absorption of calcium was estimated. 2. Changes of forearm radioactivity with time following the administration of this isotope were studied; evidence is presented that the radioactivity in the forearm at 4 h after administration of the isotope gives a valid assessment of fractional calcium absorption. 3. Fractional calcium absorption determined by this technique correlated well with the net calcium absorption as determined from stool radioactivity after oral administration of isotope. 4. In normal subjects it was shown that fractional calcium absorption measured by this technique varies inversely with the stable calcium load and that the absolute amount of calcium absorbed from given loads increases with the size of the load in the range 20–1000 mg calcium. 5. Gastro-intestinal calcium absorption was measured at various oral calcium loads in a group of fifteen patients with recurrent calcium-containing renal stones. All the patients were normocalcaemic; some had hypercalciuria. In the patients with hypercalciuria, calcium absorption, fractional and absolute, was significantly increased at all calcium loads as compared to that of patients with normal urinary calcium. 6. It is concluded that hyperabsorption of calcium from the gastro-intestinal tract plays a crucial role in the aetiology of hypercalciuria, probably by causing an increase in the renal filtered calcium load.

The Hypercalciurias CAUSES, PARATHYROID FUNCTIONS, AND DIAGNOSTIC CRITERIA

“…They were classified into various groups according to the following provisional criteria. The diagnosis of primary hyperparathyroidism was suspected when hypercalcemia and high -serum immunoreactive parathyroid hormone (PTH) 2 treatment, and 620 mg and 1,700 mg during calcium loading periods. The majority of patients and control subjects underwent studies with more than one of these regimens.…”

“…Two cases with renal stones had normocalcemia, hypercalciuria, and high urinary cAMP or serum PTH. Since CaA was less than urinaryINTRODUCTION Hypercalciuria is frequently encountered in primary hyperparathyroidism and is the hallmark of idiopathic hypercalciuria (1,2). The term resorptive hypercalciuria has been used to describe the hypercalciuria of primary hyperparathyroidism because of the frequent association of excessive skeletal resorption (3).…”

Studies in Calcium Absorption: Initial Entry of Calcium into the Gastrointestinal Tract in Hyperparathyroidism and in a Case of Renal Tubular Acidosis

“…An abnormally high calcium absorption has been described in sarcoidosis, a condition recently shown to be associated witha low level of circulating parathyroid hormone [8]. Similarly, high absorption of calcium has been demonstrated in patients with hypercalciuria in whom hyperparathyroidism has been ruled out [28]. In our patient with renal tubular acidosis, age, dietary calcium level and vitamin D intake could not account for the high absorption rate of calcium observed.…”

“…In the present study, the data of the normal controls demonstrate that absorption begins early after ingestion of the isotope and its rate reaches a peak approximately at 1.5 h. Thereafter, the absorption rate falls, and as a result the cumulative absorption begins to level out, becoming near asymp totic by 3 h. The subjects participating in this study were on a low calcium diet, which would stimulate calcium uptake [28]. Under these conditions, the range of calcium absorbed was 30 to 47% of dose at 4 h. Maximum absorption rates are seen at approximately 1.5 h after oral ingestion of the isotope.…”

“…These include formal metabolic balance studies under strict conditions; metabolic studies associated with radiocalcium studies in which stool excretion of orally or intravenously administered isotope is measured; the sampling of blood after the oral administration of a calcium tracer; and the comparison of orally and intravenously administered radioisotope sampled in whole body counting, in urine or in blood. A method of external arm count ing after intravenous and oral ingestion of tracer also has been recently reported [14,28], Most of the methods enumerated above provide us with static information, such as the relative value of radiocalcium in the blood at a given point in time after its oral ingestion, or the determination of total radiocalcium …”