I have several points, Helen.
1. I need to read the book "Date Formats for Dummies." It took me a while to realize these results were 1 per day, not 1 per month!!!
2. It is clear that Digibind has been cleared by the 7th and Bayer and Roche compare well in the absence of Digibind. It is also clear that Digibind was affecting the two assays differently on the 6th. The Bayer result could be close to the "free digoxin concentration," which is what I think should be measured during Digibind therapy. Obviously, the Roche result is much higher than the Bayer result (3x) and therefore nowhere near the free dig conc., but I suspect the Total Digoxin concentration is much higher than 1.8 ng/mL (probably much higher than 3.2 ng/mL) because the Digibind will draw dig out of tissues.
3. Advice from Bayer, "interpret with caution" is good advice, but very deficient if that's all they say. At least they ought to say how Digibind affects their assay and how long it might take to clear.
4. Roche's comment that "...no method for digoxin works in the presence of Digibind" is near true, but not entirely accurate, in my opinion.
5. The statement "..you can initially have a false low level and then a false high" may be accurate for some particular assay, but it would be method dependent and would depend on what false low and false high mean.
6. Although its been a number of years since I've paid a lot of attention to this issue, I think most methods give very high results in the presence of Digibind, but those results are probably underestimates of the total digoxin concentration in the blood at that time. The only value (limited) is that the high values give some suggestion that the Digibind is working, but not how well.
7. One or two (or maybe more now) methods (and I can't recall which ones right now) give low digoxin results that approximate the free (unbound) digoxin in the presence of Digibind. The argument has been made that patients on dig would be better off if the Digibind were titrated such that the free dig was in the therapeutic range (for total dig, which is essentially all unbound) in the absence of Digibind. That is that would be better than giving such patients so much Digibind that their free dig went to zero. On the other hand, if this was an accidental or intentional poisoning in a patient that shouldn't be on dig, it would be best to give enough Digibind to get free dig to zero.
8. We set up a procedure whereby Pharmacy notifies the lab if Digibind is ordered (usually by ER, or, I mean A&E).
9. Note added in proof: I agree with Graham Mould, whose note came after I started writing this.
-Jim
>>> "Grimes, Helen, UCHG" <[log in to unmask]> 7/20/2005 7:05:01 AM >>>
We were comparing digoxin results on a patient using Bayer Centaur, and Roche E Modular.
5.7.05 Digoxin 3.2 ng/mL Bayer Centaur Not analysed on Roche
6/7/05 0.6 1.8 ng/mL Roche
7/7/05 1.4 1.4
8/7/05 0.9 0.8
11/7/05 <0.5 <0.5
It turns out that the patient received Digibind on the 6/7/05. Bayer insert say to "interpret results with caution", Roche says Digibind manufacturer say no method for digoxin works in the presence of Digibind. Another reference I found states you can initially have a false low level and then a false high. Half life is 16-20 hours but dependent on renal function.
So looking at the above results, when is the first "true result" post Digibind? The literature states not to monitor digoxin post Digibind, but how long post Digibind? Also how many laboratories know samples are taken at correct time, and are also informed of Digibind treatment?.
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