calcium-phosphate product, ie the calcium and phosphate concentrations in mmol/l multiplied together, is diagnostically less than 2.4; normal value is 3.0
the level of 25 OH vitamin D is the best indicator of disease (1)
concentration of 25OHD below around 25nmol/L (10µg/L) is probably consistent with vitamin D deficiency in children, in which both clinical and biochemical abnormalities (e.g. rickets or symptomatic hypocalcaemia) may occur.
concentrations of 30-50nmol/L (12-20µg/L) are frequently associated with biochemical disturbances (particularly raised PTH, which is considered a sign of vitamin D insufficiency), but not clinical problems
if there is any suspicion that a child has vitamin D deficiency or rickets, the GP should measure serum concentrations of 25OHD and send the child for appropriate X-rays. If a child is found to have rickets then s/he should be referred to a paediatrician for further monitoring and treatment
Radiology:
Looser's zones are characteristic but not always present
commonly there is a picture of general skeletal deformity which may include:
crush fractures of the vertebrae
trefoil pelvis
spontaneous fractures of the ribs, pubic rami, femoral neck or the metaphyses above and below the knee
bowing of the long bones
in children - increased depth and width of the epiphyseal growth plate, and a 'cupped' appearance of the adjacent metaphyses
Bone biopsy:
decreased rate of bone turnover with excessive unmineralised osteoid - the biopsy is normal in osteoporosis
Reference:
Chanchlani R et al. An Overview of Rickets in Children. Kidney Int Rep. 2020 Apr 11;5(7):980-990
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