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Comparing Methods of Measuring Treatment Intensification in Hypertension Care
Rose AJ, Berlowitz DR, Manze M, Orner MB, Kressin NR. Comparing Methods of Measuring Treatment Intensification in Hypertension Care. Poster session presented at: AcademyHealth Annual Research Meeting; 2009 Jun 30; Chicago, IL.
Insufficient treatment intensification (TI) is an important barrier to blood pressure (BP) control. A valid measure of TI could be useful in quality improvement efforts. However, there is uncertainty in the literature regarding how best to measure TI, and a variety of approaches have been used. Our objective was to compare the ability of different measures of TI to predict BP control (predictive criterion validity).
Patients were enrolled in this prospective cohort study starting in August 2004; follow-up was completed in January, 2008. The outcome was the final BP measurement prior to study completion. Other data collected included demographics, comorbid conditions, BP values at each clinic visit, and prescriptions. We used three different methods to calculate TI. The any/none method differentiates patients who had any medication increases from patients who had none. The Norm-Based Method (NBM) models the chance of a medication increase at each visit based on patient and visit characteristics, then scores each patient based on whether they received more or fewer medication increases than predicted by the model. The Standard-Based Method (SBM) is similar to NBM but expects a medication increase whenever the BP is uncontrolled. We compared the ability of these three measures of TI to predict each patient's final systolic blood pressure (SBP), controlling for covariates, using linear regression. Dichotomous BP control (final SBP < 140 mm/Hg) was similarly examined using multivariable logistic regression.
819 hypertensive patients managed in primary care at an academic, urban safety-net hospital. The mean follow-up time was 24 months. The mean age was 60, 66% of patients were female, and 58% were of Black race. At baseline, 25% of patients received 1 medication, 37% received 2, 25% received 3, and 13% received 4 or more. The mean baseline BP was 134/80 mm/Hg.
The any/none method produced a paradoxical result: patients with any therapy increases had a higher final SBP than those who had none (134.8 mm/Hg vs. 128.4 mm/Hg, p < 0.001). NBM was not a significant predictor of BP (p = 0.28). A categorical analysis demonstrated a U-shaped relationship between the NBM score and the final SBP (final SBP in quartiles of increasing TI: 138, 128, 131, and 134 mm/Hg). The SBM score was the best predictor of BP control; the patient's final SBP was 2.1 mm/Hg lower for each additional therapy increase per ten visits (p < 0.001). Controlling for patient-level covariates did not alter this result. Patients with the most intensive management (highest quartile) had a mean final SBP 16 mm/Hg lower than patients with the least intensive management (lowest quartile). The SBM score also predicted greater odds of a final SBP < 140 mm/Hg (OR 1.30 for each additional therapy increase per ten visits, c-statistic 0.70, p < 0.001).
The SBM score was a powerful predictor of BP control, while the NBM score and the any/none score were not valid measures of TI. The validity of SBM was robust to examining BP control as a continuous vs. a dichotomous outcome, as well as controlling for patient-level covariates.
Implications for Policy, Delivery or Practice:
Our results suggest that the standard-based method is the preferred measure of treatment intensification for hypertension care. Given its strong link to BP control in our study and prior studies, treatment intensification, as measured by the standard-based method, could serve as a quality indicator for hypertension care.
Primary Funding Source: Other
Other: National Heart, Lung, and Blood Institute