The European Uremic Toxin Work Group has defined the term middle molecule to be between 500 Daltons - 60 kD. There is still a strong thought that as-yet-unidentified unfiltered middle molecules may be a major reason for the unusually high cardiovascular mortality rate of ESRD patients.
Here is a helpful list of molecular weights of some common substances:
BUN (0.06 kD). Obviously, not a middle molecule; small, cleared rapidly.
Creatinine (0.113kD). Same as BUN: cleared rapidly.
Vitamin B12 (1.355 kD). A middle molecule of lower MW which is cleared by most modern dialyzers.
B2-microglobulin (11.8kD). One of the few middle molecules whose accumulation has been shown to be associated with a real medical condition: b2-amyloidosis. Newer generation dialyzers provide good clearance of b2-microglobulin and have made the clinical entity of b2-amyloidosis much more rare.
light chain (25kD). Light chains are small enough to get dialyzed--providing some rationale for dialyzing patients with paraproteinemias (though the clinical evidence for this being effective is not very good).
albumin (66kD). Albumin is not a middle molecule--it is not appreciably dialyzed off, nor would it be desirable to do so.
3 comments:
Molecular weight of light chains is 25 kDa, but this is mainly referred to kappa light chains, that are monomeric; lambda light chains are usually dimeric, thus their MW is 50 kDa, not dialyzable with most membranes (super-flux membranes cut-off is around 50 kDa), except with high cut-off membranes.
You need a large pore membrane to dialyze paraproteinemias.
Thanks for the comment!
That makes sense regarding having to use a super-flux membrane for dialyzing paraproteinemias.
My understanding is that the reason this is not that effective in treating myeloma kidney is because the antibody is rapidly re-synthesized and thus one would need nearly constant dialysis in order to prevent renal damage from occurring.
It is not useful to dialyze a myeloma kidney without chemotherapy treatment; but if you stop the paraprotein production with chemotherapy (whatever protocol it is) you can dialyze with a large pore dialyzer in order to avoid further kidney damage.
There some trial working in that area. We will see the results
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