From the Guidelines
To evaluate rickets, a comprehensive laboratory workup should include serum calcium, phosphorus, alkaline phosphatase, 25-hydroxyvitamin D, parathyroid hormone (PTH), and renal function tests. Begin with these basic tests to assess bone metabolism and vitamin D status. According to the K/DOQI clinical practice guidelines for bone metabolism and disease in chronic kidney disease 1, if plasma intact PTH is above the target range, serum 25-hydroxyvitamin D should be measured at first encounter.
Key Laboratory Tests
- Serum calcium: may be normal or low
- Phosphorus: typically low in vitamin D deficiency rickets
- Alkaline phosphatase: usually elevated, reflecting increased osteoblastic activity
- 25-hydroxyvitamin D: levels below 30 ng/mL suggest deficiency, as per the guidelines 1
- Parathyroid hormone (PTH): often elevated due to secondary hyperparathyroidism
Additional Tests
- Urinary calcium and phosphorus excretion: to evaluate renal handling of these minerals
- Fibroblast growth factor 23 (FGF23) levels and genetic testing: may be warranted in suspected cases of hereditary forms
Diagnosis and Treatment
Radiographs of wrists and knees can confirm the diagnosis by showing characteristic widening and cupping of metaphyses. This workup helps distinguish nutritional rickets from hereditary forms and guides appropriate treatment, which typically involves vitamin D supplementation, such as vitamin D2 (ergocalciferol) 1, along with calcium supplementation in deficiency cases. The use of ergocalciferol therapy should be integrated with the serum calcium and phosphorus levels, and these levels should be measured at least every 3 months 1.
From the Research
Ricket Lab Work Up
- The diagnosis of rickets should be confirmed with characteristic radiographic abnormalities, and lab work up should include tests for serum calcium, inorganic phosphorus (Pi), liver function, 25-hydroxyvitamin D (25OHD), parathyroid hormone, creatinine, and potassium 2.
- In cases of refractory rickets, assessments should be conducted for spot urine calcium, Pi, creatinine, and blood gas analysis 2.
- In children with rickets and metabolic acidosis, tests for glycosuria, uricosuria, aminoaciduria, low molecular weight proteinuria, and albuminuria should be conducted 2.
- 1,25(OH)2 D and fibroblast growth factor 23 estimation is useful for certain forms of phosphopenic rickets 2.
- Management of rickets includes close monitoring of growth, the degree of leg bowing, bone pain, serum phosphate, calcium, alkaline phosphatase, parathyroid hormone, 25-hydroxyvitamin D3, and calciuria 3.
- An adequate calcium intake and normal 25-hydroxyvitamin D3 levels should be assured in all patients, and children with calcipenic rickets require supplementation or pharmacological treatment with native or active vitamin D depending on the underlying pathophysiology 3.
Biochemical Analysis
- Biochemical analyses should include tests for serum alkaline phosphatase, which is a surrogate marker of osteoblast activity and thus degree of rickets 3.
- Serum levels of calcium, phosphorus, and 25-hydroxyvitamin D should be monitored to assess the effectiveness of treatment 4.
- Urine tests should include spot urine calcium, Pi, and creatinine to assess renal function and phosphate reabsorption 2.
Genetic Testing
- Genetic tests may be necessary to diagnose hereditary causes of rickets, such as X-linked hypophosphatemic rickets (XLH) 5.
- Genetic testing can help identify mutations in genes involved in vitamin D metabolism or action, renal phosphate reabsorption, or synthesis, or degradation of the phosphaturic hormone fibroblast growth factor 23 (FGF23) 4.