[Exploration of renal tubular functions]

The vital role of the kidneys is closely related to their interior homeostatic function that provides a protection to the cells regarding the consequences of environmental variations of the organism. Any primary or secondary damage caused to the tubular functions may impair this homeostasis. Two indications justify an analysis of these functions: the search for and characterization of a primary defect of one or several tubular functions and the detection of early alterations of tubular functions in glomerular renal diseases. Following a brief overview of physiological aspects, the positive and aetiologic diagnosis of a tubular alteration is described, whatever the way the disorder have been detected, aetiologic analysis of a metabolic disorder or specific screening using a dynamic test. Main criteria used to determine the renal or extrarenal origin of the metabolic disorders are reviewed. General principles are described, together with the indication and interpretation of the most current investigation procedures for proximal tubular reabsorption (calculation or measurement of bicarbonate, phosphate, or glucose Tm), distal NaCl reabsorption (response to diuretics, hypotonic saline load test), concentration/dilution (dDAVP water restriction test, water load test) or distal urinary acidification (acid load, bicarbonate load, furosemide test). Last, as a conclusion, we highlight the possibility of performing routinely genetic diagnosis of most hereditary tubular diseases (Bartter/Gitelman syndrome, nephrogenic diabetes insipidus, distal tubular acidosis, and Lowe and Dent syndromes).