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FLC assays: sensistive test works well for some, not others

Posted on July 02 2014 by Pat Killingsworth | 1,983 views

It’s wonderful to have so many dear online friends looking out for you.  When suzierose commented–and then emailed me–suggesting that a FLC assay would be a more sensitive and accurate way to measure the progress that pomalidomide was or wasn’t makingm  I responded that I wasn’t familiar with that test.  Coincidentally, that’s one of the test results Danny Parker and his doctors use to monitor his myeloma levels, too.

Danny then followed up with a column about it:

More about alternative ways to monitor myeloma


Alarm bells should have been going off in my head.  How could I be a patient at top rated Moffitt Cancer Center and Mayo Clinic and not had this test done?

I’ve been so busy lately I didn’t take the time to check my own test results before responding. For me, checking certain lab numbers becomes a habit.  I often remind readers to pay attention to trends up or down.  That means monitoring the same numbers month to month.  So I follow a few key values and skim over the rest.   I learned that my doctors have been following my FLC assay ratio  for years!  FLC is an acronym for free light chains.   Moffitt’s reports doesn’t use the acronym.  Mayo Clinic does.

In a post I wrote earlier in the month, myeloma survivor and activist, Jack Aiello, called me on some inaccurate (sloppy) writing I’d done, referring to my free light chain ratio as “zero.”   Of course a ratio can never be zero.  It should have read, “one.”  What I meant to convey was that no myeloma activity was present in that test.

Blame it on chemo brain, being crazy busy with our move across the State of Florida, my pain or pain meds.  Why I failed to make the connection between my exchange with Jack, suzierose’s suggestion and Danny’s concern over his report showing a rising FLC ratio is beyond me.

Come to think about it, I’m not the only one who’s cognitively challenged here!  How many times have I written that the only reliable number my doctors have to work with is my M-spike?

Why haven’t my doctors suggested I pay more attention to My FLC ratio?  Because for me it’s  an unreliable measure.  Just as electopheresis testing of my urine always registers as normal.  I double checked.  My FLC assay ration runs in a narrow (normal) range between 1.0 and 1.7.  And it doesn’t necessarily rise when my M-spike does.  It was 1.17 when my M-spike was 0.2, 1.69 at 0.4 and  now that my spike is up to 0.7, the ratio is inexplicably down to 1.02.

Remember a while back when I wrote about trying to find a back door into several clinical trials that might have worked for me?  Each required an M-spike of at least 1.0, or an FLC ration of 10.  No go.  It’s the post I mentioned earlier that Jack commented about:

Clarification: How to qualify for a clinical trial


I spoke with Danny Parker by phone last evening.  It was great to hear his voice!  Danny wanted to remind me and our readers that often, the FLC assay isn’t necessary.  But in situations like his–where his doctors are trying to determine if his slumbering myeloma is awakening–or mine, where a more sensitive test might help determine if a new therapy is on track–FLC results can be a useful tool.  Just because it doesn’t work for me doesn’t mean it won’t work for you!

And from my standpoint, this is further evidence that Dr Alsina’s non-theory may hold some weight.  After all, it is strange that testing my urine shows nothing.  My IgG and IgA numbers are fine.  FLC ratio is OK.  My latest bone marrow biopsy (it was last year) showed no  myeloma cells.  And yet my bones are starting to look like Swiss cheese!

I’m proof that testing for–and monitoring–multiple myeloma still has a long way to go.

I do have a solution: stick me in the circus and let me entertain medical visitors with my amazing bones full of holes!  There’s an example of my long lost sardonic wit!

Feel good and keep smiling!  Pat

13 Comments For This Post

  1. Mary Says:

    Hey Pat!

    Um, so, when I have a complete Myeloma workup done, which right now is every 90 days, on the lab report I get back where it says K/L light chain ratio, free, serum …. is that the same thing as FLC assay?

  2. Holt Says:

    Thanks for the article on light chains Pat (and others who contributed). I just wanted to add a couple of points. First, just to make this measure a bit more confusing, different labs report light chains in different ways. Mayo (and probably some others) report light chains as milligrams per deciliter, that is per tenth of a liter. Many other labs report them as milligrams per full liter so results from these labs will be 10 times higher than results from Mayo. This isn’t a problem if you stay at the same lab and track your trends from month to month and it also doesn’t affect the ratio. However if you move from lab to lab or are trying to communicate your results to another MMer you have to make sure that you’re comparing apples to apples.

    Second, sometimes the light chains can be a problem in and of themselves and not just an indicator of your myeloma activity. When I was diagnosed all my immunoglobulins were normal but my kappa light chain concentration was 20 times higher than normal. The light chains clogged my kidneys resulting in kidney failure which was confirmed by a kidney biopsy (fortunately sedated). To this day, 4 years after diagnosis and treatment, my immunoglobulins remain normal but my light chains still bounce around a bit with the kappas never quite getting back to normal. My doctors don’t even have a good name for this variant of MM, further evidence that this is frustratingly diverse disease.

  3. Ron Harvot Says:


    Very interesting. I am just the opposite. I have never had a real measurable M spike on the SPEP test and my Immumofixation shows only a faint sign in the IGg Kappa area. When I was diagonsed the sFLC Assay showed that the Kappa band was way above normal and my ratio was high with Lambda band being low normal. I had some lytic lessions and was anemic. Thus I was diagnosed with stage II IgG Kappa MM. The sFLC Assay is the test I focus on.

  4. Nick van Dyk Says:

    Pat –

    Not to be a PITA — me, never, haha! — but for patients like you, regular BMB and PET may be the only way to track the disease. Was your disease resurgent a year ago when your last BMB was clean? If so, then I’m at a loss. But PET don’t lie.

    The reason Barlogie requires BMB and PET from patients that have normal serum under immunofixation and normal light chains is precisely what you are encountering: when MM returns, it can come back in a form that doesn’t secrete in protein or urine. I’ve not heard of MM that doesn’t show up under bone marrow, but as we all know bone marrows can come up clean in one area and polluted with MM in another. I would think it would be odd for one to have disease that appears to be progressing pretty rapidly in your bones and have clean bone marrow, but I’m not a doctor.

    It all points to regular advanced imaging. Another area where UAMS used to be accused of major over testing (and this still happens — a Mayo Scottsdale doctor made fun of UAMS in a recent MMRF-hosted event) but centers are coming around. After that Mayo doctor left, the five other doctors on the panel all talked about how PET and MRI are needed to assess the disease.

  5. Nancy Shamanna Says:

    Hi Nick, From my admittedly limited knowledge of myeloma testing, I think that all ‘non-secretory’ type patients are tracked by MRI, PET and BMB’s. But possibly the difference between the UAMS and other medical institutions (especially here in Canada) is that you are being regularly tested with the more invasive tests even if you have no symptoms, and are generally thought to be in a good remission, or even have no MRD.

    I know I am just tracked right now with serum tests, but have no CRAB symptoms in particular. Probably there is more that could be done that way, but we work under constraints in a publicly funded system that you may not have encountered! When I read posts like yours I can’t help but worry though!!

  6. DougC Says:

    The Huntsman also conducts extensive testing. I’ve been in CR since Jan 08. However, I receive FLCA every three months with bone marrow biop every six months and an alternating MRI or PET/CT every six months. The first two years I had labs and biopsy every two months if I remember right.

  7. nil desperandum Says:


    you mention an FLC ratio of 10 for clinical trial eligibility. So this would need to be the “involved/uninvolved” ratio, not be the standard kappa/lambda ratio. I.e. if one is a lambda secreter then the lambda/kappa ratio, and if one is a kappa secreter then kappa/lambda ratio.

    A commonly used FLC-based eligibility requirement for RRMM trials is: “involved FLC >=10 mg/dL (>= 100 mg/L) provided serum FLC ratio is abnormal”

    Dr. Libby provides definitions of both clinical relapse and “paraprotein relapse” for those not demonstrating clinical relapse at this link:

    including both M-protein and FLC-based criteria.

  8. Danny Parker Says:

    Great discussion. However, Nil Desperandum’s comments are very much on target.

    Note that the FLC definition of relapse is quite rigorous and the involved free light chain (iFLC) must be >= 100 mg/L (or in other cases 200 mg/L) for two consecutive tests with an abnormal FLCR.

    For context, my current iFLC is 22! One reason why there’s not much reason to be too excited (yet).

    Still, as Nick mentions, there are those where they exhibit no signs of MM in serum or urine. That’s why BMB, MRI, PET and clinical evaluations are so important.

    Unfortunately, meyloma is a complex disease and that’s good reason to be treated by those with a solid understanding of the many nuances of diagnosis and treatment.

  9. Pat Killingsworth Says:

    I was traveling yesterday; back on the Gulf Coast to pick up one of the last loads of stuff from the house we’re selling there. Where are we going to put all the stuff?

    Anyway, I missed the opportunity to address all of the helpful comments and questions one by one.

    Since its become crystal clear that this isn’t my strongest myeloma related area (I should have taken more math and science instead of opting out for my lucrative career as a social studies teacher), I’m going to step aside and let our brilliant readers address “milligrams per deciliter.”

    But I did want to answer Mary’s question with a resounding, “Yes, I believe so.”

    And I wanted to remind Nick that I’ve now had a pair of PETs in the past five months. Unfortunately, each has shown more activity than the last. My myeloma was not active during my last BMB.

  10. Nick van Dyk Says:

    Pat –

    Thanks for the reminder. So the answer is more frequent PET and BMB for you, unfortunately, to stay on top of this.

    As a means of comparison (for you and others), here was the PET schedule for me at UAMS.

    Upon presentation (January, 2009) — to confirm diagnosis

    Prior to beginning therapy (early February, 2009) — for staging before commencing therapy

    After one week of therapy (February, 2009) — measured tumor response to therapy; there is strong correlation between success of therapy and immediate reduction in tumor activity

    Before first transplant (April, 2009) — restaging plus full measurement of impact of induction

    Before second transplant (~ June, 2009) — restaging plus measurement of impact of transplant one

    Following consolidation (~August, 2009) — measurement of transplants and consolidation (CR reached)

    Thereafter annually while in remission.

    So twice in five months doesn’t sound that aggressive to me! 😉

    Have a great 4th!

  11. Pat Killingsworth Says:

    Let’s put it this way. I’m guessing if we try in another four months my insurance company will fight back! Unfortunately, insurance too often dictates how often–and what type of test–we get. I think they get our doctors “trained,” too. PETs are a relatively new thing for myeloma patients out in the “real world.” But they’ve obviously caught on–and for good reason. You have a great holiday weekend, too!

  12. Leigh McCulloch Says:

    My FLC ratio has stayed stable for the last year with the Kappa/ Lambda ratio around 8. I have had 3 BMB’s during that time and each time the level of myeloma cells has gone up (in total around 20%. I will have to ask my specialist why this is happening!

  13. Pat Killingsworth Says:

    Good example of how myeloma indicators aren’t always on the same page. Good idea to ask your doctor about it…

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