Investigations

1st investigations to order

x-ray of a long bone

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Result
Test

X-rays 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@55c91277

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's zone (pseudofracture)

serum calcium

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Result
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Normal values 2.3 to 2.7 mmol/L; as low as 1.9 mmol/L in neonatal period.[3]​​[5]

Result

may be decreased in hypocalcaemic rickets; normal in hypophosphataemic rickets

serum inorganic phosphorus

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Result
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Normal values vary with age.

Neonatal period: 1.6 to 3.0 mmol/L; adolescence: 0.9 to 1.5 mmol/L.[3]​​[5]

Result

may be decreased in hypocalcaemic rickets; decreased in hypophosphataemic rickets

serum parathyroid hormone level

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Result
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Normal values vary with age and method: 1 to 6 picomoles/L.[3]​​[5]

Result

high with hypocalcaemic rickets and normal with hypophosphataemic rickets

25-hydroxyvitamin D levels (calcidiol)

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

Result

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

alkaline phosphatase and liver function tests

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Result
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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 rickets

serum creatinine and urea

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Result
Test

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

Result

raised 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 hypophosphataemic rickets in the absence of vitamin D deficiency.[25] TRP is normally >80%.[24]

Result

urinary calcium is decreased and urinary phosphorus is increased in hypocalcaemic rickets; urinary calcium is normal and urinary phosphorus is high in hypophosphataemic rickets

Investigations to consider

1,25-dihydroxyvitamin D levels (calcitriol)

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Result
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Normal values 43 to 139 picomoles/L; up to 250 picomoles/L in pre-term 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 hypophosphataemic rickets (hypophosphataemia 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 hypocalcaemic rickets as a result of parathyroid hormone action; usually normal in hypophosphataemic forms of rickets

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