Serum Chemistry: Standards/Reference Material

[DrBaboon]

I have a couple notions on this topic, but I want to put some more time into what I'll post about what I think is the way to go - so I'll save that for later.

Hypothetical Situation: You're fortunate enough to have equipment and supplies (reagents, etc.) to be able to perform a few blood/serum/plasma chemistries, and this is will be a prolonged experience.

Let's leave performing Whole Blood Glucoses (ordinary diabetic test strips & meters) out of the discussion - they have their own needs if you're going to do QA, and they are less needy from a calibration standpoint, even separate from QA.

Regular labs have materials that they buy or make that has known amounts of the substances they plan to measure, and use those materials to calibrate their instruments (generally at least as often as they run a batch of tests - might be daily, weekly or perhaps more than once a day). They also use similar materials to validate the results they are obtaining.

Since these types of supplies are not being delivered due to whatever contingency we've confronted in this situation... What do we do to get materials to calibrate our chemistry testing (at least once in a while)?

Let's say you have a jar of urea from the local school laboratory. Can you simply make up a urea solution and use it as a standard to calibrate your BUN test?

Since serum or plasma is a completely different "matrix" and not the same as a simple solution of urea in water, you're not likely to get good results doing something like this. The materials labs buy or make are essentially artificial serum/plasma to duplicate much of the "matrix" for the substance being measured.

You could use a "pool" of serum from people in your group to set up a "normal" for each test. That might help somewhat for some needs.

You could "spike" a batch of serum (pooled or otherwise) with the substance you intend to measure, but that will only give you a reference comparison.

Again - I have a suggestion for how to meet these goals, and I'll post that later.

Any discussion now?

[52bravo]

real good point drbaboo, as a medical studen i in a lot of difference hospital how have there own labs, and the lab ref mat is some times difference.
so i alway look them up the first week in a new hospital.

frank

[DrBaboon]

I'm not sure that my choice of words in english made the leap to danish. ;) Sorry. Ask my wife - she'll tell you I am confusing at times... :D

Let's say that we had some supplies and a Bausch & Lomb Spectronic 20 from a high school chemistry lab, and intended to do a wet measurement of serum BUN (urea nitrogen - or the analgous urea itself). I don't know the SI norms for urea nitrogen in mmol/L. Common units in the US are mg/dl. Depending on the lab - US expected ranges might be 7-23 mg/dl more or less.

So suppose we got that assay operating. How do we calibrate or standardize our assay on a day we run specimens? How do we convince ourselves that we can rely on the results that we have obtained on BUN?

You can ask similar questions for any other substance being measured in blood.

Under austere circumstances - we would not have a standard "serum" to calibrate the assay nor would we have a similar supply of material to show that we are able to agree with a known BUN in a proficiency standard.

I can think of 2 ways to do this.

Anyone heard of "standard additions?" It's a technique commonly used in natural water chemistry or analyses of complex substrates such as sewage/sludge. The problem with these types of materials, is similar to analysing serum or plasma - they are a specific matrix which affects results, so you can't compare them to simple aquaeous solutions of the substance being analysed.

The other thing about "standard additions" is that the assay itself becomes the standard/calibration/result, and to some extent the proficiency/validation. It takes a few more steps, but seems to be a way to "solve" some of the challenges we'd face in chemistries done under austere circumstances.

The other way I can think to do this, would be similar to standard additions, but would be done on pooled serum, and then compare our unknown serum sample to the pooled serum.

The standard additions method might consume more supplies, but would give a result that is an actual number. The 2nd approach would tell you that the unknown serum result was x amount over (or perhaps under) the pooled serum value. It would not end up telling an actual result, since we probably would not know the exact BUN in the pooled serum. However, this would probably consume less total supplies if we did a fair number of BUN measurements daily.

If we were only doing 1-2 BUNs per day - it would not be a big difference.

I can fill out some of the details on this if it would help. Let me know.

Again - I simply mention BUN as an example. This really is meant to be a discussion of calibration and validation of blood chemistry results when you have to commercially available standards.