Differential Diagnosis
- Single most likely diagnosis
- Hyperglycemia: Given the high plasma osmolality (Posm 300) and high urine osmolality (Uosm 1100) with normal serum sodium, hyperglycemia is a likely cause. The high glucose levels can contribute to increased osmolality in both plasma and urine.
- Other Likely diagnoses
- Diabetes Insipidus (DI): Although less likely than hyperglycemia due to the normal serum sodium, DI (especially central DI) could present with high urine osmolality if the patient is partially responsive to ADH or has been treated. However, the plasma osmolality being high also points towards a state of hyperosmolality which could be seen in uncontrolled diabetes mellitus rather than DI alone.
- Hypertriglyceridemia: Severe hypertriglyceridemia can cause pseudohyponatremia due to laboratory measurement issues, but with normal sodium levels reported here, it's less likely. However, it could contribute to increased plasma osmolality.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Severe Hypernatremia with Pseudonormalization: Although serum sodium is reported as normal, any condition leading to severe hypernatremia (e.g., dehydration, DI) that has been partially corrected could present with these osmolality values. Missing this could be critical.
- Mannitol or Other Osmotic Agent Intoxication: Ingestion or infusion of mannitol or other osmotic agents can increase both plasma and urine osmolality. This is a critical diagnosis to consider due to its potential for severe neurological and renal complications.
- Rare diagnoses
- Glucose-Galactose Malabsorption: A rare genetic disorder leading to malabsorption of glucose and galactose, which could potentially increase urine osmolality due to the presence of these sugars in the urine.
- Other Osmotic Diuresis Causes: Certain conditions like sorbitol or xylitol intoxication can cause an osmotic diuresis, increasing urine osmolality. These are rare but should be considered in the appropriate clinical context.