Introduction Vitamin D deficiency occurring after gastric bypass procedures can predispose patients to calcium and parathyroid hormone (PTH) level abnormalities. The aim of the study is to identify pre-operative patient risk factors for post operative vitamin D deficiency.
Methods: We retrospectively reviewed patients who underwent Roux-en-Y gastric bypass (short limb= 75 cm, long limb= 165 cm) procedures at our institution from January 2005-October 2006. Patient demographics, laboratory values of calcium, vitamin D and PTH were followed at quarterly intervals for one year. Statistical analysis included paired t-test for continuous variables and Fisher’s exact test (FET) for categorical variables. A backward stepwise logistic regression model was used to predict probability of post operative vitamin D deficiency.Results 145 patients were included in the study after 50 patients were eliminated for incomplete follow up. The mean age for the group was 44 ± 10 years with an average body mass index (BMI) of 49.5 kg/m2. 86% of patients were female and 23% of the population was African American. Forty two percent of the patients had vitamin D deficiency (<20 ng/mL) either pre-operatively or at year one, with minimal change in mean values over the one year (25.7 -> 25.0 ng/mL, p=0.54). However, the mean calcium levels decreased significantly from 9.39 to 9.16 mg/dL (p<0.001) while the mean PTH levels increased significantly from 25.7 to 43.9 ng/mL (p<0.001) over the same period. On univariate analysis, post operative vitamin D deficiency was associated with higher pre-operative BMI (51.1 vs 48.4 kg/m2, p=0.037), African American race (FET, p=0.0002), long limb bypass (FET, p= 0.017), lower pre-operative calcium levels (9.27 vs 9.47 mg/dL, p=0.018) and lower pre-operative vitamin D levels (19.9 vs 30.0 ng/mL, p<0.0001). Age, sex, reduction in BMI and pre-operative PTH levels did not appear to affect post operative vitamin D values. A logistic regression model used to predict post operative vitamin D levels recognized pre-operative vitamin D levels, race and bypass limb length to be the only significant factors (p<0.05).Conclusion Our study identified several characteristics that predispose patients for vitamin D deficiency after the bypass procedures. However, only pre-operative vitamin D values, race and limb length were significant for predicting post operative vitamin D values. It is important to recognize these patients who are at risk before surgery so that early intervention could be in place to minimize further post operative deficiency.