Abstract
Introduction
The calcium-PTH-vitamin D-axis has long been highlighted for its effects on bone status and much interest has been given to how this relates to the risk of sustaining an osteoporotic fracture. Little attention has on the other hand been given to how disturbances in this axis, as for example secondary hyperparathyroidism (SHPT), relate to mortality among hip fracture patients. We therefore wanted to determine if SHPT could predict mortality in this group of patients.
Methods
The study included 562 hip fracture patients (HF) (age 70 years) admitted to a Danish university hospital. Each hip fracture patient was exactly matched according to age and sex with two controls randomly chosen from a control population of approximately 248000 subjects. The control group (Con) (n=1124) consists of subjects who have had PTH, total calcium (Ca) and 25OH-vitamin D (VitD) measured at the General Practitioners Laboratory of Copenhagen after referral from their general practitioner. Of the HF's 462 had a Ca measurement, 440 had a PTH measurement and 439 had a VitD measurement.
Basic characteristics (values for age, Ca, PTH and VitD are mean (SD)): Sex (females/males) (%): 73.8/26.2. Age (years): 82.9 (5.7). Ca (mmol/l): Con 2.34 (0.13), HF 2.27 (0.13), p<0.0001 (chi-square). PTH (pmol/l): Con 6.4 (5.8), HF 6.6 (5.4), p=0.4 (chi-square). VitD (nmol/l): Con 53.3 (30.1), HF 49.3 (29.6), p=0.02 (chi-square).
Results
General 1-year mortality (dead/total): Con-female 9.2% (76/830), Con-male 17.7% (52/294), HF-female 24.6% (102/415), HF-male 33.3% (49/147), p<0.0001 (log rank).
Prevalence of SHPT defined by PTH>7.1 pmol/l and VitD<50 nmol/l: Con 18%, HF 20%, p=0.2 (chi-square).
SHPT and related 1-year mortality (dead/total): Con-nonSHPT 9.7% (89/922), Con-SHPT 19.3% (39/202), HF-nonSHPT 22.7% (78/343), HF-SHPT 34.9% (30/86), p<0.0001 (log rank).
Discussion
Our study clearly shows that SHPT is a significant predictor of mortality in both hip fracture patients and the control group as mortality is significantly higher among subjects suffering from SHPT. The effect of SHPT on mortality appears early on among the hip fracture patients after which the mortality parallels the other groups. In accordance with the literature, we found that the general 1-year mortality among hip fracture patients is significantly increased compared to an age- and sex-matched control group.
The fact that the prevalence of SHPT is not significantly higher among the hip fracture patients than in the control group in our study is a bit surprising but might be due to a higher degree of awareness of vitamin D deficiency among elderly patients at risk of hip fractures and a higher level of vitamin D supplementation in this group.
