Osteocalcin and specific markers of bone resorption in sickle cell disease

Sickle cell disease commonly causes avascular necrosis of bone. Plain radiographs are not useful if obtained early in the disease. Radionuclide scans do not appear to increase the sensitivity of the diagnosis. Magnetic resonance imaging can detect disease but this is expensive and hard to employ on a routine or regular basis. The determination of the following new biochemical markers of bone metabolism has not been previously performed in sickle cell disease: serum osteocalcin (S-BGP), urinary cross-linked aminoterminal telopeptide of type I collagen (INTP or NTx) and urinary deoxypyridinoline (U∼DPD). As a first step or preliminary study we evaluate the usefulness of these biochemical markers of bone metabolism, by measuring the plasma or serum and urine levels of these markers in 20 adult patients with sickle cell disease. There was no change in S-BGP (p<0.9) a biochemical marker of bone formation. The two markers of bone resorption, urinary NTx (p<0.002) and U-DPD (p<0.001) increased highly significantly. Although the mean values of urinary NTx and U-DPD were significantly elevated in five patients with clinical evidence of bone complications, only two of these subjects had values above mean +2 SD of normal (control) mean values. Hence the sensitivity and specificity of these measures need to be further investigated with a larger sample size. There was significant correlation (P < 0.001) between NTx and U-DPD. These preliminary findings indicate that urinary NTx and U-DPD should be further investigated as possible biochemical markers of skeletal changes in SCD.