Differentiating AVP deficiency and primary polydipsia: a clinical and biochemical perspective

Abstract

Aims: The polyuria–polydipsia syndrome encompasses three major disorders—arginine vasopressin (AVP) deficiency, AVP resistance, and primary polydipsia. This study aimed to differentiate AVP deficiency from primary polydipsia by evaluating clinical features, biochemical markers, and anterior pituitary hormone levels, using the water deprivation test as the primary diagnostic modality. Methods: This retrospective observational study included 34 adult patients with polyuria–polydipsia syndrome who underwent a standardized inpatient water deprivation test. Patients were categorized into AVP deficiency (complete or partial) or primary polydipsia based on urine osmolality responses to dehydration and desmopressin. Clinical data, daily fluid intake, and nocturia frequency were recorded. Serum electrolytes and anterior pituitary hormones (LH, GH) were analyzed. Results: AVP deficiency was diagnosed in 76.4% of patients (58.8% complete, 17.6% partial), while 23.5% had primary polydipsia. LH and GH levels were significantly higher in the primary polydipsia group (p=0.011 and p=0.028, respectively), whereas AVP deficiency was associated with lower gonadotropin levels, especially in postoperative cases. Serum sodium, chloride, and magnesium levels were significantly lower in primary polydipsia (p<0.05), reflecting dilutional hyponatremia. Urine osmolality was significantly higher in primary polydipsia (p=0.011), indicating preserved concentrating ability. Nocturia occurred in 96.2% of patients with AVP deficiency versus 12.5% in primary polydipsia (p<0.001). Conclusion: The water deprivation test remains a valuable diagnostic tool for differentiating AVP deficiency from primary polydipsia. These retrospective findings may serve as predictive indicators in the differential diagnosis, particularly in clinical settings where water deprivation tests and copeptin testing are not readily available. Incorporating nocturia frequency, serum electrolytes, and anterior pituitary hormone levels particularly LH and GH may improve diagnostic precision and facilitate individualized management.

Keywords

• Polyuria–polydipsia syndrome
• arginine vasopressin deficiency
• primary polydipsia
• water deprivation test

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