Polyuria

1. BIOCHEMICAL INVESTIGATION OF
POLYURIA
DR IDOWU, A. A
CHEMICAL PATHOLOGY,
EKSUCOM/ EKSUTH, ADO- EKITI

2. DEFINITION
• Polyuria is defined as excretion of more than
3litres of urine per day

3. CAUSES
• Drugs eg Diuretics, Lithium, Demeclocycline
• Diabetic Mellitus
• Psychogenic Polydipsia
• Diabetes insipidus: Cranial, Nephrogenic
• Syndrome of inappropriate Secretion of Antidiuretic
Hormone (SIADH)
• Metabolic: Hypercalcaemia or Hypokalaemia

4. CAUSES Contd…
• Chronic renal failure
• Thyrotoxicosis
• Iatrogenic:
Intravenous fluid, Mannitol infusion
• Cerebral trauma, tumours & infection
• Alcohol
• Massive tissue damage causing ureamia

5. INVESTIGATIONS
• Confirm true polyuria. Take 24 hours urine and measure
volume
• Serum Sodium, Potassium, Urea & creatinine
• Serum Calcium
• Plasma Glucose
• Accurate input and output chart monitoring
• Plasma osmolality
• Urinary osmolality >750mmol/Kg
• Urine/Plasma osmolality ratio >1 N

6. INVESTIGATIONS Contd
• Thyroid hormones
• Urine/Plasma Osm ratio < 1 …>>> Water
deprivation test

7. WATER DEPRIVATION TEST
PROCEDURE
• Water or food intake is stopped 8pm the night before
the test. (This must be closely supervised)
ON THE DAY OF THE TEST
• By 8am(i.e 12 hours of deprivation) The patient empties
the bladder
• -- Blood and urinary osmolalities are measured
• * If plasma osmolality is Low-Normal or Low >>>
Polyuria is appropriate
• * If plasma osmolality is HN or High, and Urinary
osmolality is > 750mmol/Kg THE TEST SHOULD BE
STOPPED

8. RESULTS AND INTERPRETATION
Post-water
deprivation
Post-water
deprivation
Post-DDAVP
Plasma
Osmolality
(mmol/Kg)
Urine
osmolality
(mmol/Kg)
Urine
osmolality
(mmol/Kg)
Interpretation
285-295 >750 >750 Normal
>295 <300 >750 Cranial DI
>295 <300 <300 Nephrogenic
DI
DDAVP=1-desamino-8-D- arginine vasopressin

9. PRECAUTIONS