How do you report a titer result?

[Dansket]

AABB Technical Manual defines "titer" as the reciprocal of the dilution of test serum that causes 1+ agglutination with the test cells. Thus, anti-D antibody that gives 1+ agglutination at a dilution of 1:64 is reported as a titer of "64" not "1:64".

 

How does your facility report titer values?

[Malcolm Needs ☆]

We would ALWAYS report this as 64, rather than 1 in 64 or 1:64.

[Yanxia]

Me,too.

[David Saikin]

Ditto

[SMILLER]

Right

[Dr. Pepper]

Ditto to Dave's ditto.

 

Oddly, our state dept of health reports quantitative RPRs as 1:64. But that's the government for you. I imagine that's at least 2 FTEs with a nice pension after 20 years to put all those "1:"s in front of the titers.

[tbostock]

Ditto to Dave's ditto.

 

Oddly, our state dept of health reports quantitative RPRs as 1:64. But that's the government for you. I imagine that's at least 2 FTEs with a nice pension after 20 years to put all those "1:"s in front of the titers.

Ours too; yeah, good luck trying to tell them they are incorrect.

[aafrin]

We too report it as 64.

[Mabel Adams]

64.  

 

We also report a score.  Do others do that?  One of the titration procedures in the Tech Manual includes calculating a score but the other doesn't.

[Malcolm Needs ☆]

We have not calculated a score for many years now Mabel.

[Mabel Adams]

I wanted to drop the score soon after I came here but I found out that our reference lab reports scores and they felt that some physicians made use of the information so I haven't changed it.  The titer method in the Technical Manual that includes scores is the one for testing HTLA-like antibodies; the method listed in the perinatal testing methods does not include scores which is why I was going to drop them.

[StevenB]

In the current addition of the AABB Technical manual, method 3-15 Antibody Titration Procedure states the following in the Interpretation section:

 

"Titer values alone can be misleading if the strength of agglutination is not also evaluated."  It goes on to say, "The arbitrary assigned theshold for significance in comparing scores is a difference of 10 or more between test samples."

 

Although not listed under the Prenatal Titration method, in my opinion the Interpretation section of the Antibody Titration Procedure applies to all titrations.

 

If a lab is performing titration studies, but is not doing comparative studies between previous samples, then scoring and reporting the score serves no purpose.  However, if previous samples are stored frozen and then tested in parallel with a current sample, then scoring and reporting the score can provide useful information.

 

Recently, I have been working on a prenatal patient that supports this point.  The first three times we saw the patient, the antibody that was present did not react in the test phase we use for prenatal titrations (saline tube, 60 min, 37C to AGT, Heavy-chain specific IgG).  On the fourth submission the antibody had a titer of 2, score 15.  The fifth submission the results were: titer 8, score 34 for the current sample.  Tested in parallel, the previous sample's titer and score were 2, and 15.  Per the technical manual and many other resources, the titer result was considered clinically insignificant.  However, the increase in score represented a significant change (per the Technical Manual) and was reported as such.  The latest sample had the following results:  Current Titer/Score: 16/43.  Previous Titer/Score: 8/33.  At this point, both the titer, and the change in score were significant. 

 

While I'm not suggesting that "scoring" is for everybody, in this case we were able to alert the physcian that significant changes were occuring.  Although the titration results were still within the "insignificant" range, we were able to notify the physician that signficant changes were occuring two weeks prior to the titer finally reaching the "clinically significant" level of 16.

[David Saikin]

I score

[Yanxia]

The fifth submission the results were: titer 8, score 34 for the current sample.  Tested in parallel, the previous sample's titer and score were 2, and 15.  Per the technical manual and many other resources, the titer result was considered clinically insignificant.

StevenB,your post is marvelous, but I think titer 8 and 2 were significant, do I remember wrong? I t is more than 2 tube of titer.

[Mabel Adams]

I consider a 4 fold-rise in titer to be significant.  The 16 cut-off for Rh antibodies is the point at which it is recommended to follow the patient by doppler ultrasound etc. rather than just continued titers.  I don't think of that cut-off as defining "clinically significant" or not.

[AMcCord]

Definitely would report 64. I had to argue with our director (a chemist) about that, but won the argument after I showed him the Technical Manual.

[StevenB]

Per shily:

"The fifth submission the results were: titer 8, score 34 for the current sample.  Tested in parallel, the previous sample's titer and score were 2, and 15.  Per the technical manual and many other resources, the titer result was considered clinically insignificant.

StevenB,your post is marvelous, but I think titer 8 and 2 were significant, do I remember wrong? I t is more than 2 tube of titer."

 

Thanks shily.  I would have responded earlier but I'm not seeing beyond the first page in these posts.

 

We follow the Technical Manual's recommendation when determining clinically significant increases which states: "In comparative studies, a significant difference in titer is three or more dilutions."  In this instance, the first observable titer was 2.  That sample was frozen and run in parallel with the next sample that demonstrated a titer of 8.  That is a two tube increase and per the TM, not a significant change.

 

I suppose though, one could argue that when compared to the initial test results, where the antibody was "nonreactive in the test phase used for titration studies" (not <1) that the titer of 8 fell into the "three or more dilutions" increase.  Right or wrong, we only do the comparison to the previous sample.  But it is food for thought, thanks much.

 

[ANORRIS]

What do you use for positive and negative controls?

[David Saikin]

What do you use for positive and negative controls?

 

I already know the antibody; I do not run controls for this - just the previous specimen and a homozygous cell (the same for each).

[Malcolm Needs ☆]

I already know the antibody; I do not run controls for this - just the previous specimen and a homozygous cell (the same for each).

 

Why cells giving supposed homozygous expression, and not cells giving supposed heterozygous expression David?  If this is for prediction of the severity of HDFN, surely heterozygous would be closer to the in vivo situation?