This document discusses investigations for urine and blood tests to evaluate potential causes of polyuria or renal disease. Urine tests can check for diabetes, renal disease, and diabetes insipidus. Blood tests evaluate renal function, electrolytes, calcium, thyroid function, and look for signs of myeloma, collagen disease, or pituitary disorders. Further investigations may include imaging of the renal tract, renal biopsy, and imaging of the brain to identify tumors. Water deprivation and desmopressin tests can help distinguish cranial vs nephrogenic diabetes insipidus.

1. Investigations

2. Investigations
• Urine tests:
• Blood tests:
• Further investigations:

3. Urine tests:
 Diabetes -glucose, ketones)
Renal disease- Protienuria
 Specific gravity -diabetes insipidus
psychogenic polydipsia

4. 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

5. • Quantification of proteinuria: 24-hour urine
collection;
• microalbuminuria

6. • 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

7. • Spot urine sodium
• Water deprivation test, if suspect diabetes
insipidus
• 24 hour urinary calcium level

8. 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

9. • Urine electrophoresis: Light-chain
immunoglobulins (Bence Jones protein):
myeloma may be the cause of hypercalcaemia.

10. Blood test
• Renal
function, electrolytes, calcium: Potassium
deficiency, abnormalities suggesting chronic
renal failure and hypercalcaemia.
• Thyroid function tests

11. • 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.

12. • 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

13. •Autoantibody screen: If collagen
vascular disease is a possible cause of
renal failure.
•Serum lithium concentration if
relevant.

14. 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.

15. – Renal biopsy.
– Lateral skull X-ray: May show an enlarged
pituitary fossa with pituitary tumours.
– Calcification is common with
craniopharyngiomas.

16. – 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