Bone Abstracts (2014) 3 PP365 | DOI: 10.1530/boneabs.3.PP365

Alkaline phosphatase bone isoform B1x: a marker of impaired osteoblastic function in patients with renal osteodystrophy

Mathias Haarhaus1,2, Marie-Claude Monier-Faugere3, Per Magnusson2 & Hartmut Malluche3


1Division of Clinical Chemistry, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden; 2Department of Nephrology, Karolinska University Hospital, Stockholm, Sweden; 3Division of Nephrology, Bone and Mineral Metabolism, Albert B. Chandler Medical Center, University of Kentucky, Lexington, Kentucky, USA.


Renal osteodystrophy encompasses the bone histologic abnormalities seen in patients with chronic kidney disease (CKD). The bone-specific alkaline phosphatase (BALP) isoform B1x is exclusively found in serum of some CKD patients. The aim of this study was to examine the relationship between serum BALP isoforms and histologic abnormalities of bone in patients with CKD on chronic dialysis (CKD-5D).

Anterior iliac crest bone samples from 40 CKD-5D patients were selected from the IRB approved Kentucky Bone Registry based on the level of bone turnover. There were samples from 40 patients with low and non-low bone turnover. Bone histomorphometry was performed using the Osteoplan system. BALP levels were measured by an ELISA assay. BALP isoforms (B/I, B1x, B1 and B2) were determined by HPLC. Parathyroid hormone (PTH) levels were measured using an electrochemiluminescence assay.

B1x was found in 21 patients (53%). BALP, other BALP isoforms, PTH, osteoblast number (NOb/BPm), and activity (Obv) were lower in these patients compared to patients without B1x (Table). B1x correlated inversely with osteoblast number and activity (r=−0.30 and −0.26 respectively, P<0.05).

BALP (U/l)B/I (μkat/l)B1 (μkat/l)B2 (μkat/l)PTH (pg/ml)NOb/BPm (#/100 mm)Obv (%/day)
B1x+24.3±3.240.13±0.020.53±0.091.57±0.24141±38.3*77.1±19.40.27±0.07
B1x−69.6±14.00.24±0.031.44±0.305.72±1.81484±106333±94.30.50±0.09
Mean±S.E.M.; *P<0.05; P<0.01.

This study shows that the release of B1x from bone into serum is a sign of perturbed osteoblast activity. Measurement of B1x may provide a valuable tool for the assessment of patients with renal osteodystrophy.

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