Olfactory function has been shown to be affected in chronic kidney disease; however, studies are contradictory and little is known on the effects of dialysis. To resolve these issues we tested olfactory function in 24 healthy controls and in 28 patients with chronic kidney disease receiving hemodialysis (20 patients) or peritoneal dialysis (the other 8). As assays for olfactory function we measured smell identification, n-butanol and acetic acid thresholds, Kt/V urea, percentage reduced urea, and weights before and after dialysis. Olfactory function was also self-rated by the participants. Compared to healthy controls, predialysis olfactory function was moderately but significantly decreased in the two dialysis groups, with hemodialysis patients being more affected. Patients self-rated olfactory function similar to that of healthy controls, suggesting that patients are unaware of the olfactory decrease. Olfactory function was significantly improved by one hemodialysis session. Neither body mass index, total volume loss, nor any other dialysis parameter correlated with olfactory function or its restitution following hemodialysis. The observed pattern of improvement suggests underlying mixed peripheral and central mechanisms. Thus, olfactory dysfunction in patients with chronic kidney disease is readily reversible by hemodialysis.

Better retronasal than orthonasal olfactory function seems to be associated with the presence of mechanical obstruction in the anterior portion of the olfactory cleft. In turn, these data indicate that olfactory loss in NP seems to be caused by regional mechanical or inflammatory factors.

Olfactory function and nNO concentration correlate in chronic rhinosinusitis patients but not in healthy subjects. This suggests that both parameters do rather not directly influence each other but it might be the inflammatory processes found in chronic rhinosinusitis that affects olfaction and nNO. Nasal nitric oxide produced by the paranasal sinuses seems not to directly influence olfactory function.

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The majority of patients with olfactory disorders seek medical advice before presenting to a specialist Olfaction Clinic. However, the majority reported receiving no or poor information about their diagnosis and prognosis. Considering the significant prevalence and potential consequences of olfactory disorders, it is our duty as specialists to improve the knowledge and communication of our medical colleagues about these diseases, so that patient education or referral can be improved.