Hypophosphatasia

TO THE EDITOR: I read with interest the article, "A Practical Approach to Hypercalcemia," (1) in the May 1, 2003, issue of American Family Physician. In addition to the causes of hypercalcemia that were listed in the article, family physicians who take care of infants also may want to consider other etiologies (see accompanying table). (2)

I also would be interested to know whether the authors think that substituting a spot urine calcium/creatinine ratio for a 24-hour urine calcium level is acceptable for evaluation of these infants. Timed urine collections can be difficult, especially in children.

REFERENCES

(1.) Carroll MF, Schade DS. A practical approach to hypercalcemia. Am Fam Physician 2003;67:1959-66.

(2.) Claudius IA, Fattal O, Nakamoto J. Hypercalcemia. Accessed March 9, 2004 at: http://www.emedicine. com/ped/topic1062.htm.

JAMES E. SPRINGATE, M.D.

251 Old Lyme Dr.

Amherst, N.Y. 14221

IN REPLY: In infants, hypercalcemia is a rare but serious condition which should be investigated and treated without delay. The most common causes are iatrogenic administration of calcium (generally intravenously) and idiopathic infantile hypercalcemia, of which Williams syndrome is the severe variant. (1) Severe primary hyperparathyroidism and homozygous familial hypocalciuric hypercalcemia presenting in the neonatal period may require rapid surgical intervention. As with adults, if hypercalcemia is confirmed with an elevated ionized calcium level, the measurement of intact parathyroid hormone level is the pivotal step in evaluation of the causative disorder. Calculation of a calcium/creatinine ratio using a random spot urine specimen correlates well with total 24-hour urinary calcium excretion. (2) In the diagnostic algorithm for hypercalcemia, the urinary calcium/creatinine ratio can be used as a convenient and accurate substitution for a timed urine collection in term and preterm infants. (3)

REFERENCES

(1.) Rodd C, Goodyear P. Hypercalcemia of the newborn: etiology, evaluation, and management. Pediatr Nephrol 1999;13:542-7.

(2.) Gokce C, Gokce O, Baydinc C, Ilhan N, Alasehirli E, Ozkucuk F, et al. Use of random urine samples to estimate total urinary calcium and phosphate excretion. Arch Intern Med 1991;151:1587-8.

(3.) Trotter A, Stoll M, Leititis JU, Blatter A, Pohlandt F. Circadian variations of urinary electrolyte concentrations in preterm and term infants. J Pediatr 1996;128:253-6.

Hypercalcemia in Infants

Williams syndrome

Autosomal recessive hypophosphatasia

Secondary hyperparathyroidism from maternal hypocalcemia

Blue diaper syndrome

Jansen metaphyseal chondrodysplasia

Subcutaneous fat necrosis

Dietary phosphate deficiency

MARY F. CARROLL, M.D.

Eastern New Mexico Medical Center

Roswell, N.M.

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