The Fantus test was first described by J.B. Fantus in 1936.⁴ It was originally used for the diagnosis of salt and water depletion and for the differential diagnosis of edema.⁵ However, this test has been found to be particularly useful for monitoring sodium intake in individuals with blood pressure disorders, including both hypotension and hypertension.

Since 1904 when Ambard and Beaujard ⁶ first implicated salt as a major factor in the pathogenesis of hypertension, conflicting opinions and data have confused this issue. In 1944, Kempner⁷ published a classic article describing the effective treatment of essential hypertension using a salt-restricted “Rice Diet.” Many studies have subsequently demonstrated the effectiveness of salt-restricted diets in treating hypertension.⁸^–¹² Substantial evidence now exists that sodium alone does not raise blood pressure as had been previously thought, but rather that chloride also plays an important role in the elevation of blood pressure when consumed as sodium chloride, or common table salt.^13,¹⁴ Sodium bicarbonate has not been found to have the same hypertensive effect as sodium chloride.

The Fantus test is an indirect test for sodium and actually measures chloride ion concentration. Considering that sodium chloride intake, rather than sodium ion alone, is a significant factor in blood volume expansion and blood pressure elevation, the Fantus test may be more clinically useful than direct tests for urinary sodium when managing hypertension or fluid retention.^13,¹⁴

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