What’s the relationship here?
In the 1990s, a paper in NEJM described
the first relationship of the two. Pseudohyponatremia has been classically described
with intravenous gamma globulins. Pseudohyponatremia is a laboratory artifact due
to hyperlipidemia or hyperproteinemia. Intravenous infusion of immune globulin
increases the protein load and as a result the protein phase of serum is higher. Depending on the type
of laboratory test used, some centers might note a low Na. Usually, the serum
osmolarity then would be normal clinching the diagnosis.
Another
mechanism that has been proposed is a form of hypertonic hyponatremia – the one
you would see in mannitol or hyperglycemia.
most IVIG preparations contain significant amounts of sucrose or maltose
leading to the increased osmolarity and leading to fluid shifts leading to
hyponatremia. The magnitude of the Na drop might depend on renal function as
well and clearance of sucrose.
Finally, a
dilutional variant has been noted as well ( Sosm would be low) and you would
have a true hyponatremia due to the volume of IVIG infusion that leads to a
form of water intoxication.
Take a look at this case series that combines the latter to mechanisms in their presentations of IVIG induced hyponatremia. Here is another case report.
