Diabetes Insipidus, Part 2

Diagnosing DI

Polyuria = urine vol > 3L in 24 hrs - there are many causes of polyuria and it is important to figure out if the cause is DI or something else prior to establishing treatment

Urine osmolality (osm) of > 300 mOsmol/kg + high serum glucose --> think diabetes mellitus
Urine osmolality (osm) of > 300 mOsmol/kg + high serum urea --> think renal dz
Urine osmolality (osm) of < 200 mOsmol/kg + polyuria --> think DI

So you have a patient that has urine ohm < 200 + polyuria and you are thinking DI... how do you differentiate between central DI and nephrogenic DI?

Answer: water deprivation test

Findings:
Central DI
urine osm < plasma osm after dehydration
after ADH injections urine osm increases by >50%

Psychogenic DI

urine osm > plasma osm after dehydration

after ADH injections urine osm increases minimally

Nephrogenic DI

urine osm < plasma osm after dehydration

after ADH injections urine osm increases by <50%

Source: 
Makaryus/Mcfarlane. DI: diagnosis and treatement of a complex disease Cleveland Clinic Journal of Medicine Jan 2006 Vol 73:1
pic source: medicaltextboks.blogspot.com

Calculating and Interpreting ABI

http://www.strokescaninc.com/abi.htm

First things first...
What does ABI stand for? 

Ankle-Brachial Index

What arteries are you examining?

Brachial and Dorsalis pedis

How do calculate ABI?

R ABI = highest avg ankle pressure (R dorsalis pedis)/ highest avg arm pressure (either arm)
L ABI = highest avg ankle pressure (L dorsalis pedis)/ highest avg arm pressure (either arm)

http://www.mayoclinic.com/health/medical/IM04412

How do you interpret the #s?

ABI                     Interpretation

>0.90                   Normal LE flow

<0.89 - >0.60      Mild PAD

<0.59 - >0.40      Moderate PAD

<0.39                   Severe PAD

See more about the technique of gathering ABI data in an older ABI post of mine...



Source: Bates Pocket Guide of Physical Examination 6th Ed