Differential Diagnosis for Frequency Urine

Single most likely diagnosis

• Primary Polydipsia: This condition is characterized by excessive fluid intake leading to frequent urination. The urine osmolality (Uosm) of 1100 mOsm/kg suggests that the kidneys are able to concentrate urine, but the high fluid intake (suggested by Posm 300) is causing the frequent urination. The negative urinalysis (Ua neg) and normal electrolytes (Lytes nml) support this diagnosis.

Other Likely diagnoses

• Diabetes Insipidus (DI): Although the Uosm is not as low as typically seen in DI, a partial deficiency in antidiuretic hormone (ADH) or renal resistance to ADH could still cause frequent urination. However, the Uosm of 1100 mOsm/kg is higher than expected in DI.
• Overactive Bladder: This condition is characterized by a sudden, intense urge to urinate, often with frequent urination. However, it would not typically affect urine osmolality or electrolytes.

Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

• Diabetic Ketoacidosis (DKA): Although the Lytes are normal and the Ua is negative, DKA can sometimes present with minimal ketonuria. The high Posm could be a clue to hyperglycemia, and missing DKA could be fatal.
• Hypercalcemia: Hypercalcemia can cause polyuria, but it would typically be associated with other symptoms and abnormal electrolyte levels.

Rare diagnoses

• Nephrogenic Diabetes Insipidus: A rare condition where the kidneys are unable to respond to ADH, leading to polyuria. However, the Uosm of 1100 mOsm/kg is higher than expected in this condition.
• Psychogenic Polydipsia: A rare condition where excessive fluid intake is driven by psychological factors, rather than thirst. It could present similarly to primary polydipsia, but would require a different treatment approach.