Download Slide ()

Algorithms for differentiating the three major types of diabetes insipidus (DI). In a patient with polydipsia and polyuria, a 24-hour urine osmolarity less than
300 mOsm/L and a negative test for glucosuria, there are two ways to determine the type of DI. One is to measure plasma arginine vasopressin (AVP)
under conditions of unrestricted fluid intake. If it is high (>2.5 pg/mL) when the urine is dilute, the patient has renal (nephrogenic) DI and an MRI of the
brain is not necessary. However, if plasma AVP is low (<1 pg/mL), a brain MRI to determine if the hyperintense signal (“bright spot”) normally emitted by
the posterior pituitary (PP) is present or absent will indicate whether the patient has primary polydipsia or pituitary DI. It may also reveal evidence of
pathology responsible for the disorder. The other way to differentiate DI is to perform a fluid deprivation test with hourly measurements of urine osmolarity
Source: Disorders of Water Metabolism, Pediatric Endocrinology and Inborn Errors of Metabolism, 2e
as well as plasma osmolarity or plasma sodium. If the urine osmolarity does not rise above 300 mOsm/L before plasma osmolarity or sodium reach the
Sarafoglou
K, range,
Hoffmann
GF, polydipsia
Roth KS. Pediatric
Endocrinology
Inborn Errors
Metabolism,
20172 Available
at:the injection of
upper limit ofCitation:
the normal
reference
primary
is excluded
and repeat and
measurements
of of
urine
osmolarity2e;
1 and
hours after
http://mhmedical.com/
Accessed:
June
10,
2017
desmopressin suffice to determine if the patient has severe pituitary or severe nephrogenic DI. However, if fluid deprivation results in concentration of the
© 2017 McGraw-Hill
Education.
All rights
urine before Copyright
plasma osmolarity
or sodium reach
the upper
limit reserved
of normal, repeat measurements of plasma AVP as well as plasma and urine osmolarity
before and after an infusion of 3% saline will be necessary to reliably distinguish between primary polydipsia, partial pituitary DI, and partial nephrogenic DI