Instructions to patient

Why do we do this test?

This test is done to exclude Diabetes insipidus, a condition in which your kidneys cannot concentrate urine.

Where will the test be done?

Medical Day Unit (PARK UNIT) Trafford General Hospital 0161 7462279

The test will take the whole day. Please bring in some food if you have any special requirements). It is important that you let the nurse know if you feel unwell in any way. You will be closely monitored through the test Please bring some reading material

On day of water deprivation test: No tobacco/alcohol for 24 hrs before the test Avoid caffeine on day of test. If you are on any regular medications, please ask your doctor. You can take regular medications but avoid DDAVP and diuretics ( Water tablets) for 24 hours. You must take all prescribed hormones (eg Hydrocortisone, Estrogen, Testosterone – if any)

Have your normal breakfast around 6 AM.

You will be able to have dry foods (eg nuts, bread through the day when you are hungry).

Have normal amounts of fluids as you normally do BEFORE the test. do not dehydrate yourself.

You will be given an injection/ Nasal spray at 4:30 AM. Please let the nurse know if you have any allergies

Directions Water Deprivation test morning only

  1. Week before test
  2. Notify biochemistry department regarding urgent processing of urine and blood samples.. They are not to be batch sampled! You need instructions in real-time. Please email duty biochemist
  3. Write out a prescription for Desmopressin 2 mg IM as a stat dose Alternative would be Intranasal spray (20 mcg spray to be administered)
  4. Ring patient to ensure that if they have diabetes, their diabetes is reasonably well controlled ( Average blood glucose <10 mmol/l) (HbA1c <69 mmol/mol)
  5. Day of the test
  6. An F1/ F2 needs to be present nearby to monitor and supervise.
  7. Label samples correctly incorrect labelling makes the test difficult to interpret.
  8. Weighing scales need to be present
  9. A measuring jug for urine volume
  10. Urine osmolality containers.
  11. Bleep duty biochemist at Trafford to inform.
  12. What do you need to watch for?
  13. Any patient symptoms
  14. Blood pressure and pulse ( Signs so f dehydration)
  15. Weigh the patient and ( >3% weight loss ) eg. 100 kg down to 97 kg is significant – ABORT TEST
  16. Plasma osmolality >300 mosm / l at any point
  17. Ensure Samples reach laboratory
  18. Patient should not smoke, or drink water unobserved. No unsupervised visits to toilet
  19. When should you not proceed with test
    1. Baseline sodium >145, serum osmolality >295 mosm/l,
    2. Patient unwell (low blood pressure, tachycardia
    3. Any infection/ Stress
    4. When anterior pituitary hormones have not been replaced (eg hydrocortisone)
    5. Renal failure/ Uncontrolled diabetes
  20. What are you looking for?
    1. Urine ability to concentrate >750 before DDAVP – Normal
    2. Urine between 300 – 750 mosm/l – Psychognic polydipsia /Partial DI
    3. Urine <300 mosm – Diabetes insipidus
    4. Response to DDAVP
      1. Rises to >750 Cranial DI
      2. Rises to 350 – 750 Nephrogenic DI

 

  1. Schedule for the test – Test Starts at 7:30 AM Abbreviated Test
Time Urine Vol Weight Sodium Urine Osm Serum osm
7:30 AM Discard

 

 

 * * * *
Test Starts 8 AM Stop water Abort if Na>145 Abort if osm >300
9 AM
9AM

 

 *

 

 

 * * * *
10 AM * * * * *
11 AM * *
12 Noon * *
1 pm

 

 *

 

 

 * Notify if weight loss >3 % * *
2 PM

 

 *

 

 

 *
3 PM * * Notify if weight loss >3  % * *

4 PM Administer 20 mcg Desmopressin Nasal spray

5 PM Collect last specimen for urine osmolality and Blood osmolality

6 PM Collect urine osmolality, Blood osmolality urea and electrolytes

7 PM patient can be discharged if well

 

  1. You must get the result of each blood and urine test within 1 hour (from the lab) from 8 AM to 12:30 PM
  2. Ask patient to monitor urine volume hourly for next 3 hours after discharge and keep a record.
  3. Please notify Dr. George if there are significant changes (eg symptoms, rise in Serum osmolality>300, rise in sodium >145 , drop in weight >3%)
  4. Please keep a record of the numbers above and notify Dr. George by email (egress switch/ encrypted)
  5. Do not discuss “possible diagnosis” with the patient unless you are certain of the diagnosis. Some tests return inconclusive results due to washout of renal medullary osmolality in compulsive water drinking. The results can be discussed with Dr. George and you can call to discuss results on the next day.