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Abstract
Central diabetes insipidus (CDI) is characterized by hypotonic polyuria due to impairment
of AVP secretion from the posterior pituitary. In clinical practice, it needs to be
distinguished from renal resistance to the antidiuretic effects of AVP (nephrogenic
DI), and abnormalities of thirst appreciation (primary polydipsia). As nephrogenic
diabetes insipidus is rare in adults, unless they are treated with lithium salts,
the practical challenge is how to differentiate between CDI and clinical disorders
of excess thirst. The differential diagnosis is usually straight forward, but the
recommended gold standard test, the water deprivation test, is not without interpretative
pitfalls. The addition of the measurement of plasma AVP concentrations improves diagnostic
accuracy, but the radioimmunoassay for AVP is technically difficult, and is only available
in a few specialized centres. More recently, the measurement of plasma copeptin concentrations
has been claimed to provide a reliable alternative to measurement of plasma AVP, without
the sampling handling challenges. In addition, the measurement of thirst ratings can
help the differentiation between CDI and primary polydipsia. Once the diagnosis of
CDI is biochemically certain, investigations to determine the cause of AVP deficiency
are needed. In this review, we will outline the diagnostic approach to polyuria, revisit
the caveats of the water deprivation test and review recent data on value of adding
AVP/copeptin measurement. We will also discuss treatment strategies for CDI, with
analysis of potential complications of treatment.