Urine osmolality Early morning urine sample plasma osmolality. A high plasma osmolality and inappropriately low urine osmolality –D I Both plasma and urine osmolalities are correspondingly low- psychogenic polydipsia
• Quantification of proteinuria: 24-hour urine collection;• microalbuminuria
• Microscopy and culture• 24 hour urine volume and 24 hour fluid intake should be measured to determine if urine volume is substantially increased or normal• Low urine osmolality in diabetes insipidus
• Spot urine sodium• Water deprivation test, if suspect diabetes insipidus• 24 hour urinary calcium level
24 hr urine collection• Clean, 5 liter, plastic container with 10 ml of acetic acid during normal fluid & food intake• PU is > 40 ml/kg body weight per day• Urine Osmolality < 300 mOsm/kg of water• Urine Specific Gravity <1.010• PD is water intake of > 100 ml/kg per day• Measure Plasma Sodium on that day
• Urine electrophoresis: Light-chain immunoglobulins (Bence Jones protein): myeloma may be the cause of hypercalcaemia.
Blood test• Renal function, electrolytes, calcium: Potassium deficiency, abnormalities suggesting chronic renal failure and hypercalcaemia.• Thyroid function tests
• Fasting (preferable) or random glucose• Full blood count, ESR:• Anaemia - chronic renal failure and collagen vascular diseases.• Bone marrow infiltration- myeloma.• ESR raised in collagen vascular diseases, myeloma and malignancy.
• Serum protein electrophoresis: For monoclonal immunoglobulin band in myeloma.• Hormone profile if pituitary disease is suspected. Pituitary hormones (LH, FSH, TSH, ACTH, prolactin, GH), if suspect pituitary diabetes insipidus
•Autoantibody screen: If collagenvascular disease is a possible cause ofrenal failure.•Serum lithium concentration ifrelevant.
Further investigations:– These investigations (and some of the urine and blood tests) are more likely to be part of secondary care investigations.– Imaging of the renal tract: Ultrasound, X- ray, CT scan of the abdomen.
– Renal biopsy.– Lateral skull X-ray: May show an enlarged pituitary fossa with pituitary tumours.– Calcification is common with craniopharyngiomas.
– MRI or CT scan of brain: For pituitary or other brain tumour.• Water deprivation and desmopressin test: May be performed under supervision in secondary care and is useful in distinguishing cranial and nephrogenic diabetes insipidus