Investigations

Biochemistry:

• reduced serum calcium and phosphate
• increased alkaline phosphatase
• decreased urinary calcium
• 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
• with respect to site of impaired mineralisation:
  • the distal ulna is the site that best demonstrates the early signs of impaired mineralisation, and the metaphyses above and below the knees are more useful sites in older children (2)

Bone biopsy:

• decreased rate of bone turnover with excessive unmineralised osteoid - the biopsy is normal in osteoporosis

Reference:

1. Chanchlani R et al. An Overview of Rickets in Children. Kidney Int Rep. 2020 Apr 11;5(7):980-990
2. Nield LS, Mahajan P, Joshi A, et al. Rickets: not a disease of the past. Am Fam Physician. 2006 Aug 15;74(4):619-26.