Lack of correlation between two methods for the assessment of salt sensitivity in essential hypertension

The existence of a heterogeneous blood pressure (BP) response to salt intake, a phenomenon known as salt sensitivity, has increasingly become a subject of clinical hypertension research, and has important clinical and prognostic implications. However, two different methodologies are currently used to diagnose salt sensitivity. The aim of the present study was to compare the BP response to intravenous sodium load and depletion on the one hand, and to changes in dietary salt intake on the other, in order to assess salt sensitivity in a group of essential hypertensive patients. Twenty-nine essential hypertensives underwent two different procedures separated by 1 month: a dietary test consisting of a 2-week period of low (20 mmol/day) and high (260 mmol/day) salt intakes, and an intravenous test consisting of a 2 litre saline load over a 4-h period, followed by 1 day of low (20 mmol) salt intake and furosemide (40 mg/8 h orally) administration. BP was registered at the end of every period using 24-h ambulatory BP monitoring. In the whole group of hypertensive patients studied, both low salt intake and furosemide administration significantly (P < 0.01) decreased mean BP. Correlation coefficients of BP changes obtained using the two methodologies were between 0.3 and 0.4. Moreover, coefficients of agreement between the oral and the intravenous tests, using several cut points for BP changes, were systematically below 0.5, thus indicating a misclassification of salt sensitivity greater than 50%, depending on the method used. None of the cut points for BP changes during furosemide administration showed a good combination of sensitivity and specificity compared with changes in response to low dietary salt. The present results indicate that the diagnosis of salt-sensitive hypertension should be based on the BP response to changes in dietary salt intake, while BP response to saline and furosemide administration leads to a systematic misclassification of more than 50% of patients, even using different cutpoints for changes in BP.