Tests

1st tests to order

radiograph of a long bone

Test
Result
Test

Plain film of knees and wrists are taken when rickets is suspected.[4][Figure caption and citation for the preceding image starts]: Right wrist of a patient with vitamin D deficient rickets before treatment. His right wrist x-ray showed sclerotic and widened end plates of the radius and ulna (arrows)Seerat I, Greenberg M. Hypocalcaemic fit in an adolescent boy with undiagnosed rickets. BMJ Case Reports 2010; doi:10.1136/bcr.10.1136/bcr10.2008.1153 [Citation ends].com.bmj.content.model.Caption@33c81078

Result

widening of the epiphyseal plate, loss of definition of the zone of provisional calcification at the epiphyseal/metaphyseal interface, cupping, splaying, and fraying of the metaphysis; Looser zone (pseudofracture)

serum calcium

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Result
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Normal values 9.2 to 10.8 mg/dL (2.3-2.7 mmol/L); as low as 7.6 mg/dL (1.9 mmol/L) in neonatal period.[3]​​[5]

Result

may be decreased in hypocalcemic rickets; normal in hypophosphatemic rickets

serum inorganic phosphorus

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Result
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Normal values vary with age.

Neonatal period: 4.9 to 9.3 mg/dL (1.6-3.0 mmol/L); adolescence: 2.8 to 4.6 mg/dL (0.9-1.5 mmol/L).[3]​​[5]

Result

may be decreased in hypocalcemic rickets; decreased in hypophosphatemic rickets

serum parathyroid hormone level

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Result
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Normal values vary with age and method: 9.5 to 57 picograms/mL (1-6 picomoles/L).[3]​​[5]

Result

high with hypocalcemic rickets and normal with hypophosphatemic rickets

25-hydroxyvitamin D levels (calcidiol)

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Result
Test

Calcitriol (1,25-dihydroxyvitamin D) is the active form of vitamin D, but calcidiol (25-hydroxyvitamin D) is preferred for testing as it has a longer half-life and is found at much higher levels in the serum.

Normal values >10.0 nanograms/mL (>25 nanomoles/L).[3]​​

Result

low in vitamin D-deficient rickets, usually <10 nanograms/mL (<25 nanomoles/L); normal in genetic forms of hypocalcemic rickets and in hypophosphatemic rickets

alkaline phosphatase and liver function tests

Test
Result
Test

Levels vary with age. High alkaline phosphatase may represent a high bone turnover state.[5] Liver and biliary tract disease can cause abnormal vitamin D metabolism.[4]

Result

alkaline phosphatase is elevated in all types of rickets

serum creatinine and blood urea nitrogen

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Result
Test

Kidney disease causes abnormal calcium and phosphorus regulation and impaired synthesis of calcitriol.[4]

Result

elevated in rickets caused by kidney disease

urinary calcium and phosphorus

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Result
Test

Serum and urine values are used to calculate percent tubular reabsorption of phosphate (TRP). Low TRP is diagnostic of hypophosphatemic rickets in the absence of vitamin D deficiency.[25] Tubular reabsorption of phosphate is normally >80%.[24]

Result

urinary calcium is decreased and urinary phosphorus is increased in hypocalcemic rickets; urinary calcium is normal and urinary phosphorus is high in hypophosphatemic rickets

Tests to consider

1,25-dihydroxyvitamin D levels (calcitriol)

Test
Result
Test

Normal values 16.5 to 53.5 picograms/mL (43-139 picomoles/L); up to 96.2 picograms/mL (250 picomoles/L) in preterm babies.[3]​​[5]

Calcitriol may be normal, low, or high in relation to the reference range. Serum calcitriol concentration is inappropriately low for the prevailing phosphate level in patients with X-linked hypophosphatemic rickets (hypophosphatemia typically stimulates calcitriol synthesis), and very low in type I vitamin D-dependent rickets (pseudovitamin D-deficient rickets). In patients with type II vitamin D-dependent rickets (end-organ resistance to calcitriol), serum calcitriol concentration is usually very high.

Result

typically normal or elevated in hypocalcemic rickets as a result of parathyroid hormone action; usually normal in hypophosphatemic forms of rickets

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