Bone alkaline phosphatase besides intact parathyroid hormone in hemodialysis patients--any advantage?

BACKGROUND/AIM Bone alkaline phosphatase (bAP) is known to be an important biochemical marker of bone formation. Through the present study, we intended to find out whether there is any advantage in bAP determination, as a routine biochemical marker, besides intact parathyroid hormone (iPTH) in hemodialysis patients. METHODS In a population of 140 hemodialysis patients, bAP and iPTH were determined on four quarterly consecutive occasions. According to the values of iPTH (pg/ml) and bAP (ng/ml), patients were divided into four groups: group I: iPTH > 200 and bAP > 20, group II: iPTH > 200 and bAP < 20, group III: iPTH < 200 and bAP < 20 and group IV: iPTH < 200 and bAP > 20. Patients with higher serum phosphorus (P) (group A: P > or = 7 mg/dl) were compared with those with lower serum P levels (group B: P < 7 mg/dl). RESULTS The global correlation between iPTH and bAP (total evaluations, n = 503) was 0.32 (p < 0.001). Group IV patients tended to show a slight increase of serum aluminum (sAl) levels, which were 12.48 +/- 5.35 microg/l higher than in the patients from group I (sAl = 9.97 +/- 4.39 microg/l), group II (sAl = 10.86 +/- 4.45 microg/l) or group III (sAl = 10.92 +/- 3.92 microg/l). Significance values (Mann-Whitney) in each group, in comparison with group IV, were the following: group I: 0.004; group II: 0.062; group III: < 0.001. Group A (n = 66) showed higher iPTH levels than group B (n = 430), although bAP and sAl were both similar in these two groups of patients (Mann-Whitney): iPTH (A) = 631.0 +/- 487.7 vs. iPTH (B) = 253.3 +/- 191.6, p < 0.001; bAP (A) = 22.9 +/- 17.4 vs. bAP (B) = 20.4 +/- 13.1, p = n.s.; sAl (A) = 10.2 +/- 3.5 vs. sAl (B) = 10.8 +/- 4.4, p = n.s. For similar Al and bAP values, group A showed a much stronger iPTH/bAP correlation than group B: r = 0.67 (p < 0.001) vs. r = 0.30 (p < 0.001), respectively. CONCLUSION Although iPTH and bAP are frequently in agreement, it seems important to separate parathyroid activity given by iPTH, from bone remodelling reflected by bAP, in the presence of either a higher aluminum exposition or a well-controlled phosphatemia.