Published online by Cambridge University Press: 15 February 2010
Incidental finding on blood test.
Collapse (see Chapter 13).
Plasma sodium <130 mmol/L.
Approach to the problem
To distinguish between water overload (excessive intake or inadequate output) and sodium depletion (excessive salt loss).
Other features to look for:
Pigmented scrotum (see Chapter 11) or ambiguous genitalia (see Chapters 8 and 10) suggesting congenital adrenal hyperplasia.
Plasma potassium measurement.
Palpable kidney, or mass (renal vein thrombosis, adrenal haemorrhage).
Family history of renal problems.
Blood pressure (liable to be raised in renal rather than adrenal disorders).
May be informed by consideration of:
Postnatal age (low glomerular filtration rate in the first few days of life).
Gestational age (renal immaturity resulting in salt loss).
latrogenic: This is the commonest cause, and may start before birth, i.e. secondary to excess maternal intravenous (IV) fluid administration.
Syndrome of inappropriate antidiuretic hormone secretion (SIADH) (intracranial pathology: asphyxia, meningitis; intrathoracic pathology: pneumothorax).
Immaturity (extreme preterm infant usually from the end of first week of life).
Congenital adrenal hyperplasia (usually days 4–10).
Congenital adrenal hypoplasia.
Renal impairment, e.g. polyuric phase of acute tubular necrosis (ATN), congenital nephrotic syndrome, Bartter syndrome (hyperprostaglandin E syndrome, associated with life-threatening hypokalaemia). Congenital renal abnormality (there may be a history of polyhydramnios secondary to excessive urine output in utero).