LOW SERUM LEVELS OF ALKALINE-PHOSPHATASE OF BONE ORIGIN - A GOOD MARKER OF ADYNAMIC BONE-DISEASE IN HEMODIALYSIS-PATIENTS

Background. Adynamic bone disease was recently described to be increas ingly prevalent in the dialysis population. At present the diagnosis o f this type of renal osteodystrophy can only be made by bone histomorp hometry. We assessed the value of different biochemical serum markers in the diagnosis of adynamic bone disease. Methods. In 103 haemodialys is patients a bone biopsy was performed after double tetracycline labe lling, and the serum levels of intact PTH, osteocalcin, and the bone i soenzyme of alkaline phosphatase were determined. Bone alkaline phosph atase was measured by an optimized agarose gel electrophoretic method, recently shown to have a high accuracy, precision and reproducibility , also in the lower range. Results. In 38 (37%) of the patients the di agnosis of adynamic bone disease was histologically established. Const ructing receiver operator curves optimal cut-off levels for the diagno sis of adynamic bone disease were determined, being less than or equal to 27 U/litre for the bone isoenzyme of alkaline phosphatase, less th an or equal to 14 mu g/litre for osteocalcin and less than or equal to 150 pg/ml for intact PTH. Concentrations of bone alkaline phosphatase or intact PTH below these cut-off levels, were shown to be the best p erforming tests in the detection of adynamic bone disease as indicated by a sensitivity of 78.1 and 80.6% and a specificity of 86.4 and 76.2 % respectively. Applying Bayes' theorema, it was calculated that in th e current haemodialysis population in which a prevalence of adynamic b one disease up to 35% has been described, the positive predictive valu es for the proposed cut-off values are 75% for bone alkaline phosphata se, 65% for intact PTH and 55% for osteocalcin. Moreover, in this popu lation, levels of bone alkaline phosphatase and intact PTH below the o ptimal cut-off excluded hyperparathyroid bone disease. Conclusion. In view of the relative easy and accurate methodology for bone alkaline p hosphatase determination, the closer physiological link with osteoblas t function and the lesser expense for its determination we suggest tha t this marker is a useful tool in the non-invasive diagnosis of the ad ynamic type of bone disease in the individual patient.