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| Diagnosis | Urine Osmo (Step 1) | Urine Osmo (Step 2) |
|---|---|---|
| Primary Polydipsia | > 600 | No change |
| Central DI | < 300 | Increases > 50% |
| Nephrogenic DI | < 300 | Increases < 10% |
| Partial Central DI | 300 – 600 | Increases 10 – 50% |
Clinical review: Current state and future perspectives in the diagnosis of diabetes insipidus.
Note: Step 1 (Water deprivation) should stop when Posm > 295 mOsm/kg or weight loss > 3%. Desmopressin (Step 2) is then given to check the kidney's response to the missing or ineffective ADH.