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CHICAGO -- Certain factors may predict whether patients with hypertension can get their blood pressure (BP) under control with medication, researchers reported here.

Theirs is the first risk prediction model to identify patients who will develop refractory hypertension -- uncontrolled BP ≥ 140/90 mmHg despite optimal treatment with five or more antihypertensive drug classes -- in the 8 months after referral to a hypertension clinic, according to Michael Buhnerkempe, PhD, and colleagues of Southern Illinois University School of Medicine in Springfield.

Derived from longitudinal data from one urban hypertension clinic, the model had an area under the curve of 0.88 (95% CI 0.82-0.92), demonstrating "good ability to distinguish those who will and will not develop refractory hypertension," Buhnerkempe's group reported in a at the Joint Hypertension 2018 Scientific Sessions of the American Heart Association and the American Society of Hypertension.

Factoring into the model were age, BMI, diabetes, how much BP is above goal, and the number of adequately dosed drug classes prescribed to the patient.

The derivation cohort consisted of the hypertension clinic's patients who had adequate drug information and had an estimated glomerular filtration rate of at least 30 ml/min/1.73 m² (n=1,142).

“Once a patient is identified as being at risk for refractory hypertension, they should for sure have a thorough evaluation for secondary forms of hypertension; such an intensive evaluation is not necessary in the majority of hypertensive patients. This also affects drug selection because one of the more common forms of secondary hypertension that should be screened for, primary aldosteronism, cannot be done in a patient taking one of our most potent blood pressure lowering drug classes,” co- author John Flack, MD, MPH, also of SIU, told 番茄社区app.

Study participants showed a 2.2% rate of developing refractory hypertension.

Having few refractory hypertension patients was a weakness for the study, the authors acknowledged, noting that their model requires external validation.

Buhnerkempe's group showed in that other risk factors may also play a role in refractory hypertension.

Patients who couldn't get elevated BP under control even with optimal medical therapy were older and poorer and more likely to be African American. They also tended to have comorbidities such as chronic kidney disease, albuminaria, and diabetes, according to eight cycles of data on adults who had BP measurements in the National Health and Nutrition Examination Survey or NHANES (n=41,552).

"Some risk factors have not been consistent -- prior studies found males and younger individuals to be at risk," the investigators noted.

Why poverty, race, and comorbidities didn’t factor in the risk prediction model is because they didn’t contribute any or enough incremental information over and above the other variables included in the multivariable regression model, Flack noted.

What did not change from before was the estimated prevalence of refractory hypertension that Buhnerkempe's group came up with: 0.6% among those on antihypertensive medications and 5.9% among those with resistant hypertension (BP ≥ 140/90 mmHg while taking three or more antihypertensives or BP <140/90 while on at least four drug classes).

"Refractory hypertension is a rare phenotype and prevalence estimates are similar to other estimates in the U.S.," the authors confirmed. Previous estimates of refractory hypertension in the U.S. could have suffered from biased sampling and reliance on international data, they said.

Another finding was that refractory hypertension became significantly less common among all treated hypertensives, the NHANES study showed from 1999 to 2014.

Even so, according to Flack, “the patient and practitioner should be alerted of the exceedingly high cardiovascular risk in the setting of refractory hypertension.” Of “paramount importance” now in lowering cardiovascular risk among these patients is the identification of other cardiovascular risk factors and their effective treatment, he stated.