Urine test separates nonadherent from treatment-resistant hypertensive patients

Apr 22 2014

By Eleanor McDermid, Senior medwireNews Reporter

Researchers have used a urine test to show that about a quarter of patients with supposedly treatment-resistant hypertension are actually failing to take their medications as prescribed.

As reported in Heart, the team used high-performance liquid chromatography-tandem mass spectrometry analysis of spot urine samples to detect antihypertensive medications in 208 patients with hypertension.

“Until now there has been no simple, cheap and reliable test that clinicians can use to find out whether their patients are taking their drugs”, writes Morris Brown (University of Cambridge, UK) in an accompanying editorial.

He says that the researchers’ findings and their urine test “solve at a stroke the problem of monitoring adherence and should rapidly transform practice.”

The patients included 125 who were newly referred to a specialist hypertension centre, 66 who were being followed up for a suboptimal response to medications prescribed at the centre and 17 who were referred for renal denervation due to poor response to antihypertensives.

Overall, 25.0% of the patients were at least partially nonadherent. Of these, 10.1% were completely nonadherent, having no trace of any antihypertensive or its metabolites in their urine, and 14.9% were partially nonadherent, with fewer antihypertensives detected than prescribed. The average number of medications screened for was three and the average number detected was two.

The highest rate of nonadherence occurred among the follow-up patients, at 37.9%, with this being predominantly partial nonadherence (28.8% of the follow-up group), report Maciej Tomaszewski (University of Leicester, UK) and co-authors.

Brown comments: “That most patients do not take all their drugs all the time was probably predictable.” However, he highlights that 23.5% of the renal denervation referral group were found to be completely nonadherent, describing this as “a shock”.

“These patients may be the extremes, both among those who are non-adherent and among those referred for renal denervation”, he says. “But they account for a disproportionate and wasteful use of resource in their management.”

Average 24-hour systolic blood pressure rose from 152 mmHg among adherent patients, to 159 and 165 mmHg among partially and totally nonadherent patients, respectively, after accounting for age, gender, ethnicity and clinical category. Blood pressure also rose in line with increasing difference between the number of medications prescribed and the number detected.

Brown observes that the team previously reported that the gap between prescribed and detected drugs widened as the number of prescribed drugs increased. He says: “The lesson may be that few patients truly require six or more drugs: what they require is simplification of the drug regimen, a search for a [secondary] cause—or a psychiatrist!”

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