A variation in Bone Alkaline Phosphatase levels that correlates positivelywith bone loss and normal levels of aminoterminal propeptide of collagen Iin girls with anorexia nervosa

Anorexia nervosa (AN) is a very extended pathology among adolescent girls n owadays. These patients show a high degree of osteopenia; hence, study of t heir bone remodelling is of great interest. Serum bone alkaline phosphatase (bAP) and aminoterminal propeptide of procollagen I (PINP) provide good se nsitivity in the analysis of bone alterations in postmenopausal osteoporosi s. The aim of this study was to compare the usefulness of bAP and PINP in t he study of bone remodelling in AN, and their possible correlation with the degree of osteopenia in this pathology. In order to help in the interpreta tion of the results, levels of the beta-isomer of urinary carboxyterminal p ropeptide of collagen I (beta-CTX) have also been included. Serum bAP (IRMA ) Tandem R-Ostase, Hybritech), PINP (RIA, Orion Diagnostica) and CTX (Cross Laps ELISA, Osteometer) were determined in 41 girls with AN, aged 18.5+/-2. 2 years (mean+/-SD) and in 31 healthy control women, aged 19+/-2.3 years. B one mineral density (BMD) in lumbar spine was measured by DEXA in the AN gr oup. We found that 41 of the 43 patients had BMD z-scores under - 2. No sig nificant differences were found in the levels of serum bAP nor in PINP and beta-CTX levels between controls and patients, although values in the AN gr oup were highly variable. All the BMD z-score values were negative, and the ir absolute value correlates positively with bAP (P = 0.0279) and almost wi th beta-CTX (P = 0.0921) but not with PINP (P = 0.4627). Bone AP correlates with PINP in control girls (P = 0.017), but not in the AN group (P = 0.357 3). Patients with AN were divided into three groups according to their leve ls of bAP: low (I), normal (II) or high (III). Patients with the highest bA P levels also presented the highest increase in bone resorption, according to their beta-CTX levels, and the highest degree of osteopenia. However, va lues of PINP were similar in the three groups of patients. The bAP/beta-CTX ratios in subgroups I, II and III of AN patients were 0.035, 0.065 and 0.0 73, a finding that suggests that,AP is not indicating the real degree of bo ne mineralization in these patients, because it is a contradiction that the formation/resorption ratio should be higher in the patients who have the h ighest bone loss. These results could suggest that bone loss in AN is produ ced by an increase in bone resorption (beta-CTX), without variations in bon e matrix formation (PINP); bAP levels are a good marker in the follow-up of osteopenia degree, but not a real indicator of bone mineralization, a simi lar situation to that of osteomalacia. (C) 1999 Elsevier Science B.V. All r ights reserved.