Screening for hypercalciuria

Neonatal nephrocalcinosis: long term follow up

AIMS

To assess the spontaneous resolution of neonatal nephrocalcinosis and its long term effects on renal function.

METHODS

Fourteen very low birthweight preterm babies with nephrocalcinosis were followed up at 5-7 years of age; 14 controls were matched for sex, gestation, and birth weight. Height, weight, blood pressure, and renal symptomatology were recorded, and a renal ultrasound scan was performed. Early morning urine osmolality and creatinine ratios of albumin, phosphate, calcium, oxalate and beta microglobulin were determined. Urea and electrolytes in the study group were determined, and glomerular filtration rate (GFR) and TmP/GFR (tubular reabsorption of phosphate per GFR) were calculated. Statistical analysis was performed on a group basis using the Mann-Whitney confidence interval.

RESULTS

Mean age was 6.9 years (range 5.81-7.68). An early morning urine osmolality >700 mOsm/kg was achieved in all cases. In two cases and four controls, the calcium/creatinine ratio was >0.7 mmol/mmol. In all cases, the GFR was normal (median 132.6 ml/min/1.73 m(2) (range 104.1-173.1)). Median TmP/GFR was 1.22 mmol/l (0.73-1.61), with two having levels below the normal range. These did not have persisting nephrocalcinosis. Nephrocalcinosis was found in three of the 12 cases scanned and one control. There were no significant differences in urine biochemistry.

CONCLUSIONS

Resolution of nephrocalcinosis occurred in 75% of cases. No evidence was found to suggest that nephrocalcinosis is associated with renal dysfunction in the long term. There was evidence of hypercalciuria in the cases and controls, suggesting that prematurity may be a risk factor.

Hypercalciuria in children with febrile convulsions

BACKGROUND

The purpose of the present study was to investigate whether idiopathic hypercalciuria may be implicated in the pathogenesis of febrile convulsions.

METHODS

We studied 38 children (22 boys) with febrile convulsions (mean (+/- SD) age 3.25 +/- 1.09 years) and 45 healthy children (28 boys) of similar age who served as controls. Twenty-four hour urine calcium and phosphate, as well as serum calcium, phosphate, alkaline phosphatase and intact parathyroid hormone (PTH) concentrations were determined.

RESULTS

Hypercalciuria (urine Ca >4.0 mg/kg bodyweight per 24 h) was found in nine children with febrile convulsions (23.7%) and in three controls (6.7%). Hypercalciuric children excreted significantly more phosphate in their urine (37.0 +/- 11.6 mg/kg bodyweight per 24 h) than normocalciuric children (18.7 +/- 8.7 mg/kg bodyweight per 24 h) and controls (20.2 +/- 7.6 mg/kg bodyweight per 24 h). They also had higher serum intact PTH concentrations (49.87 +/- 15.36 pg/mL) than normocalciuric (35.39 +/- 15.67 pg/mL) and control children (28.21 +/- 14.00 pg/mL). According to the calcium-loading test, eight of nine children with hypercalciuria had the renal type of the disorder. Furthermore, hypercalciuric children had significantly more convulsive episodes (2.77 +/- 1.98) than normocalciuric children (1.86 +/- 1.24).

CONCLUSIONS

Our results suggest that renal hypercalciuria may be implicated in the pathogenesis of febrile convulsions.

Renal calcification in preterm infants: follow up at 4-5 years

AIM

To determine the consequences of renal calcification in preterm infants.

METHODS

A cohort of 11 preterm babies was studied at the age of 4 to 5 years. They had had renal calcification as neonates. Seventeen matched controls were also studied. Each child had a renal ultrasound scan, a calcium load test, and a desmopressin test for renal concentrating ability (RCA). The study group also had glomerular filtration rate (GFR) estimated, using the height:creatinine ratio, and tubular phosphate reabsorption, without phosphate load, per glomerular filtration rate (Tp/GFR) calculated,

RESULTS

In the study group the median GFR was 61 ml/min/1.73m2 (range 46-79 ml/min/1.73m2) and the median calculated Tp/GFR SD score was -0.94 (range -2.8-0.68). Five children out of the study group had ultrasonic evidence of renal calcification. There was no significant difference between the two groups in renal size, calciuria, before or after calcium load, or RCA. Eight children (three patients, five controls) had an abnormal calcium load test. The RCA of the children in the study and control groups combined was below that of published values, with a median calculated SD score -0.71 (95% CI -1.21 to -0.23).

CONCLUSIONS

There was evidence of renal dysfunction in children who had been born preterm. Renal calcification detected in the neonatal period does not seem to be a major predisposing factor for the abnormalities of renal function subsequently observed in these infants.

Urinary calcium excretion in Swedish children

Urinary calcium excretion was measured in an unselected population of 153 healthy Swedish children aged 2-18 years. Urine was collected after an ordinary meal. Urinary calcium excretion was measured as the calcium/creatinine concentration ratio (UCa/Cr) and expressed in mmol/l per mmol/l. UCa/Cr was 0.44 +/- 0.379 (mean +/- SD). As the UCa/Cr in this childhood population was not distributed in a normal manner, the results are more correctly presented as the 50th (0.33) and 97th (1.5) centiles. There was a weak but significant correlation between UCa/Cr and age, with higher values in the lower age groups. There was no correlation between UCa/Cr and the anamnestic intake of cow's milk. Repeated samples from some children showed a coefficient of variation between days of 30-40%. The upper limits of normal UCa/Cr (97th centile = 1.5; +2 SD = 1.2) in this investigation were higher than what is considered normal by others. In spite of this, none of the children had a history of renal stone disease or any other symptoms of hypercalciuria. Renal stone disease is thought to be rare in Swedish children although the real incidence is not known. The diagnosis of hypercalciuria should be based on repeated samples from an individual with symptoms and related to age-related reference values from the same population group.