[Piasa]

Which free light chain metric is more meaningful?

by Piasa on Tue Apr 19, 2016 12:49 pm

I have been diagnosed with IgG kappa MGUS.

I have test results from a serum Freelite assay and from an "Immunofixation Panel, Serum".

The former shows a standard kappa free light chain range of 0.33 to 1.94, and the latter 170 - 370.

One result went up from the previous, the second went down.

Which is more significant, and why? Which might be part of an myeloma-defining event (MDE) decision?

[Multibilly]

Re: Which free light chain metric is more meaningful?

by Multibilly on Tue Apr 19, 2016 2:43 pm

Hi Piasa,

This can get to be confusing.

First, it would be helpful if you included the units of measure and the title of the lab test.

The standard range for serum FREE light kappa is 3.3–19.4 mg/L. I'm guessing the other range you referenced is from a TOTAL kappa light chain measurement.

You really want to use the FREE light chain number when talking about multiple myeloma. TOTAL light chain test results aren't that useful when it comes to tracking multiple myeloma.

Secondly, a myeloma defining event (MDE) wrt free light chains is based on the following:

https://myelomabeacon.org/news/2014/10/26/new-multiple-myeloma-diagnostic-criteria/

"...Serum involved / uninvolved free light chain ratio of 100 or greater, provided the absolute level of the involved free light chain is at least 100 mg/L (a patient’s “involved” free light chain – either kappa or lambda – is the one that is above the normal reference range; the uninvolved light chain is the one that typically is in, or below, the normal range)"

[Piasa]

Re: Which free light chain metric is more meaningful?

by Piasa on Tue Apr 19, 2016 3:02 pm

Multibilly,

The units for the ranges I mention in the opening post are mg/dL.

The titles at the tops of the reports are, respectively,

"FREE LIGHT CHAIN - Details"

and

"IMMUNOFIXATION PANEL, SERUM ­ Detail".

Since the standard range units are in mg/dL, the Freelite 0.33 - 1.94 converts nicely to your

3.3–19.4 mg/L.

But the IF Panel's 170 - 370 mg/dL seems to be in a different universe.

My questions are, with regard to the IF Panel, Serum, and its higher absolute values.

How do the IF Panel results relate to the MDE definition? And,

Which of the two test results are more meaningful, FLC from Freelite, or FLC from IF Panel, given that one went up, the other down?

Regards,

Piasa

[Multibilly]

Re: Which free light chain metric is more meaningful?

by Multibilly on Tue Apr 19, 2016 3:40 pm

Piasa,

Again, I would disregard the total light chain results. You want to track and use the serum free light chain results. Total light chain results (which include the combination of bound and free light chains) aren't generally used in tracking multiple myeloma.

[Jer610]

Re: Which free light chain metric is more meaningful?

by Jer610 on Sun May 01, 2016 1:40 pm

I have observed a correlation between my uninvolved immunoglobulins and uninvolved light chain results. From my first immunofixation results, when they were all flagged as low, they have steady gone down almost in lockstep. This has happened even though my abnormal free light chain results have bounced around, though not by a lot. I believe that these results give a clearer picture of progressive bone marrow suppression, something that would probably be confirmed by a Hevylite assay.