switching from rabbit to monoclonal IgG

[WALTERJ]

I need to know what kind of testing is required when you switch IgG products. We currently use rabbit IgG and have to switch to murine monoclonal IgG due to manufacturing reasons. Of course we are still in the dark ages using tube-methods! Please help...

[Dawn]

It is the opinion of some that validation of a new reagent is not required unless as long as you use it according to manufacturer's directions. Of course, QC is required.

[Kochman]

It is critically important to read the ENTIRE package insert for reagents and not just the "directions for use part" when making decisions about switching reagents and validation. The brand of anti-human globulin has not been mentioned but, did you know that Gamma's monoclonal Anti-IgG will not detect antibodies that are subclass 4 whereas rabbit Anti-IgG does? Probably not a big deal and maybe even desirable but you should know these kinds of things BEFORE you put a reagent into use so you don't have to figure them out during testing.

A thought - "doing nothing" (for any issue) is usually not acceptable.

[Cliff]

Kochman,

Welcome to our forum, and thanks for your thoughtful contributions.

Would you have suggestions on a validation plan for a situation such as what Walter presented?

We are caught in a tough place ourselves. We will use a specimen up to 28 days from the time of collection (in some cases), yet the manufacturers directions state that we can only type them for 10 days (with our tube type). Where would one turn for validation suggestions? Our first thought was the manufacturer, but they could not offer any advice accept to validate our methods.

In FDA's opinion, what would be considered a valid validation? In both examples, Walter's and ours, would we run 10 tests, 20, 100? For us time is clearly a factor so we'll need to ensure that the same results are obtained up to 28 days. There is no "rule" on in-house validation and we obviously want to do the right thing. Suggestions are always welcome.

[Kochman]

First, keep in mind that the concept of validation is based on the fact that no two testing facilities are exactly alike. Validation is supposed to show that you can make the reagent work properly (meet performance specifications/expectations) in your own facility, with your own staff, your own instruments, your own adjunct reagents (for example - saline), following your SOPs, etc.

It is difficult to give detailed guidance on validation when someone asks since, as stated above, every situation is different. In general, you should think about your extremes and test at each extreme. For example, if you know your "room temperature" varies between 18 and 25 C, you should test at 18 and at 25. If testing works at both extremes, it is presumed it will work in between. Likewise you should consider things like run/batch sizes (smallest and largest), incubator temperature variability/stability, size/volume and number of sample drops, sample age (freshest and oldest), etc. The list is too long to cover here and not all variables are applicable to each validation situation. That's why you should sit down and develop a validation plan first and then go about your testing.

In this specific case (validation of change to monoclonal anti-human globulin), consider doing parallel antibody screening and identification using the range of antibodies you normally see or "worst case" antibodies like anti-Fyb, anti-Jka and anti-Jkb. Also consider parallel DATs and weak D tests. If you do both hand washing and machine washing, test using both methods. And use samples that are the oldest your SOP allows.

[Kochman]

Back in February, I posted this:

It is critically important to read the ENTIRE package insert for reagents and not just the "directions for use part" when making decisions about switching reagents and validation. The brand of anti-human globulin has not been mentioned but, did you know that Gamma's monoclonal Anti-IgG will not detect antibodies that are subclass 4 whereas rabbit Anti-IgG does? Probably not a big deal and maybe even desirable but you should know these kinds of things BEFORE you put a reagent into use so you don't have to figure them out during testing.

A thought - "doing nothing" (for any issue) is usually not acceptable.

This response was based on information provided to FDA by the manufacturer (Gamma) at the time of licensure (1992). Specifically, the manufacturer included the following limitation in it's package insert: "Examples of pure IgG4 subclass antibodies may not be detected by this reagent. Note, however, that pure IgG4 antibodies are very uncommon."

For the most up-to-date information on the specific performance characteristics of any reagent, consult the current package insert or contact the manufacturers' technical support group.

[sharol]

Re: the use of Gamma clone murine anti-IgG lacking the ability to detect IgG 4 subclass, these types of antibodies (mostly JMH and some Chido) are not clinically significant and are more of a nuisnance anyway...

Sharol

[Lcsmrz]

True words of wisdom on validation. I remember in my early years on the bench -- when I had at least some hair -- that changes would be made based on what was presented as some seminar and on what the medical director would sign-off. We got off easy and learned the rest afterwards.

Occasionally, it's because the mfr will no longer make the product or is having lot-release problems, as may be the case here. Things get sticky when time is a critical issue, and there is no other option, other than shutting down the transfusion service.

In validation plans, I also like to see the (hopefully scientific) reasoning behind your choices: why 10,12,24,500 specimens? Makes me comfortable knowing you seriously thought out and researched what you're doing. Risk assessment information with the strengths/weaknesses of the new and the old methods/reagents allows customizing the validation plan, rather than relying on one SOP. I also would expect more from a 550-bed full-service community hospital, than a brand new 50-bed ortho-only specialty facility.

[cathy s rawcliffe]

Keeping in mind that thought that each facility has it's unique situation, am sharing some observations using Monoclonal IgG. We implemented Monoclonal IgG not long sfter it first came out...and yes it was a relief not having so many "cold" antibodies showing up at coombs, requiring panels! We had AOT! Down the road tho, we still has "stuff" showing up at coombs very weakly that was indeterminate. After much investigating this issue, we determined it was unique situation involding HIV/AIds patients. We had ALOT of those kind of patients. Since their autoimmune system is totally shot, we also figured out over 17 years, we never had one AIDs patient ever develope a clinically significant antibody! Just sharing some info that might be useful!

[johna]

It is the opinion of some that validation of a new reagent is not required unless as long as you use it according to manufacturer's directions. Of course, QC is required.

I have to along with Dawn on this one (assuming that her "opinion of some" also refers to her opinion). Personally I can't see that a validation study related to a change from rabbit to monoclonal antiglobulin reagents is going to give you any relevant information. The reagents are strictly quality controlled by the manufacturer, FDA approved and the direction circular clearly spells out the protocol to follow. In addition the reagent is included in daily in-house QC. I'm not sure that anything more is necessary.

[Kochman]

I still maintain (very strongly) that some sort of comparison study, whether you call it validation or not, is neccessary in this situation, particularly if you are a transfusion service. Yes, the reagents are approved by FDA (in my Branch) but FDA requirements are minimum requirements. Some manufacturers simply meet those minimums, others exceed them.

If you are used to a certain performance level, you need to know if you can expect that same performance level with the new reagent.

For example, if treatment decisions are based on the strength of an antibody titrated and tested by the AHG method, you need to know if the new reagent will give the same endpoints as the one you have been using. If what you were using exceeds FDA's minimum standards, you might see a higher titration endpoint with your old reagent than you would with a new reagent that simply meets minimum requirements. So, if you intervene at a particular titration endpoint, this endpoint might have to be revised to be appropriate for the new reagent.

I'm happy to talk or correspond with anyone who wants additional rationale on this topic in the interest of improving their operations.

Sheryl Kochman

Chief, Devices Review Branch

OBRR/CBER/FDA

301-827-6123

kochman@cber.fda.gov