Introduction (skip if necessary)
I'm attached to *GH Clinical Lab together with 4 others (names are omitted for confidentiality purpose). In *GH, there are 2 clinical labs. One 24hr routine lab situated in the main building for routine tests (basic chemistry, LFT, TFT, Renal function, etc), and another lab in a building that some lecturer in school has been warning us, where you gotta show your pass or risk "getting shot". Here, highly specialized tests such as specific proteins (rheumatoid factor), trace metal panel (copper, zinc) and others like G6PD, homocysteine, etc, are analyzed.
Our supervisor has kindly planned a schedule for us which indicates that for the span of 20 weeks, we will spend 10 in the 24hr routine lab, 5 purely on our MP (but still gotta report for work =/) and the last 5 at the "special" lab.
The routine lab is further divided into 5 stations, based on the type of tests performed and machines used. We will spend 2 weeks each at each station.
Background Information
This week, I'm attached to a station using the Beckman Coulter Unicel DXI (below)to conduct routine tests for serum ferritin, folate (RBC and serum), Vitamin B12 (usually done with folate as both are linked by the reaction pathway for methionine synthesis), Cortisol (24h urine free cortisol and serum cortisol), PTH, testosterone, D-HEAS (precursor of sex hormones) and beta-HcG (pregnancy hormone). The other analyzer, the Johnson & Johnson's Vitros DT60 II (image further down) tests for lipase, lactate, ammonia, lithium and cholinesterase.
Beckman Coulter Unicel DXI (taken form http://www.beckmancoulter.com/products/instrument/immunoassay/UniCel_DxI_800.asp)
Johnson & Johnson's Vitros DT60 II
Assay and Analyzer
For this posting, I will elaborate on the lactate assay of the Vitros DT60 II. (I chose the DT because its small compared to other analyzers but very, very unique.)
The beauty of the DT60 lies in the fact that unlike any other analyzer, you don't have to worry about adding or changing reagents..at all. As if that isn't enough, QC is done once a day (other analyzer needs at least two QC runs a day), and calibration is only done twice a year!
Other additional but rather significant benefits will be that minimal daily maintainence is necessary (just wipe with a cotton swab) and solid waste can be dumped of really easily.
Many of you will be wondering what kind of freak analyzer is this that does not need reagent loading. Well, that is because this machine conducts tests by using a special slide containing the required reagents! So you just have to load in that slide, drop a patient fluid sample onto it, and wait for the results. The slide will then be transported into the machine to carry out the test reactions.
The below shows the various layers of this multi-layered slide (click to enlarge).
(taken from http://www.orthoclinical.com/Products/products.aspx?id=4§ion=features)
The Vitros Slide is made up of five main layers. From the top, there is an upper slide mount (for supporting purposes). The next layer is the spreading layer, which helps to distribute the patient sample evenly to the underlying layers. The third layer is the reagent layer, which contains all the reagents needed for the photometric reaction to take place. The final layers are the transparent support layer (to aid photometric absorbance reading), and the lower slide mount (similar to the upper slide, for supporting purposes).
Test principle and reactions
Principle: Colorimetric Assay
Reaction:
In the case of the lactate assay, the reaction at the reagent layer of the dry-slide consists of two main reactions.
First, lactate is oxidized by lactate oxidase (found in the reagent layer) to pyruvate and hydrogen peroxide.
Second, the hydrogen peroxide generated oxidizes the 4-aminoantipyrine, 1, 7-dihydroxynapthalene dye system (included in the reagent layer) in a HRP (horseradish-peroxidase)-catalyzed reaction to form a dye complex (red).
The slide is incubated and the intensity of the dye complex is measured using the in-built spectrophotometer to quantitate the lactate values using its absorbance (at 555nm).
Notes:
This colorimetric assay has an approximate five minutes incubation time. When the test is complete, the results will be printed out immediately from the DT60 analyzer in the form of a narrow result slip. The results are written down on a form and filed into the LIS. The result slips are then torn off and clipped together with the result forms in a file.
Request form with attached heparinized tube in ice- Samples must be sent in ice (bag containing ice in water) to prevent anaerobic glycolysis from producing lactic acid!
Clinical Significance of Lactate test
Reference Range: 0.90 -1.70mmol/L
Elevated lactate levels indicates lactate acidosis. Lactate levels increase in many conditions and may aid the monitoring of conditions such as diabetes mellitus. In diabetes mellitus, renal failure may result, causing metabolic acidosis. Elevated lactate levels are also useful in diagnosis of tissue hypoxia, in which there is cellular glycolysis, hence causing respiratory acidosis.
Finally a raised lactate level may be used in the screening of malignancies.
Last Words
Hope you've "enjoyed" reading the post. Do feel free to ask questions. Thanks!
P.S. Answer turnaround time: About 24hrs (from the next working day).
Signing off!
Kent Lieow
TG01
0503261J
15 comments:
Hi Kent,
You mentioned that increased lactate levels can be used in the screening of malignancies right, how does malignant tumors increase the lactate level?
Ming Boon
Tg01
Hello Kent,
You mentioned QC for Vitros DT60 II is done once a day while other analyzer needs at least two QC runs a day. Why is this so?
Since the reagents are found on the glass slides, are there any QC done on them?
Thanks!
Royston
TG02
Hello!
Just want to ask you, is this lactate test very popular? I mean is this test part of a package, just like B12 and folate are? or is it a solely ordered test?
Sally
heyheys kent,
is there any case where the lactate level dropped below the reference range? and what does it indicates?
you mentioned that the colorimetric assay has an approximate five minutes incubation time. why does it need to be incubated? at what temperature?
thanks!
dorothy
tg01
hey,
Just want to find out something, what happens when, lets say you receive a sample that is leaking water from it? do you request for a new sample or continue with the test and just add a note that the bag was leaking?
Randall
TG02
0503272G
HELLO Kent,
the Johnson & Johnson's Vitros DT60 II tests for lipase, lactate, ammonia, lithium and cholinesterase.
May i know that's the clinical significants of testing lithium, ammonia and cholinesterase? What will the results imply if it's not within reference range?
Heyy guys! Thanks for spending time to read thru the blog posting! As of now, I’ll answer some queries first. As for the rest, I ain’t too sure of my answer so do be patient. Thanks! =)
To Ming Boon,
As you know, the fastest way to kill tumour cells is to expose them to oxygen. Malignant cells grow in an oxygen-deprieved location thus they only and can only make use of anaerobic glycolysis. The by-product of anaerobic glycolusis is lactic acid, hence the elevated lactate levels.
To Royston,
Erm, I think it’s a mistake on my part to put running of only 1 QC a day as a benefit of the Vitros DT. QC is usually done twice on other analyzers which are running for 24 hrs. One in the morning and the other in the afternoon (abt 3pm) for the staffs on night-shift. However the Vitros DT is not running 24 hrs, so QC is done once only in the morning.
QC’s are done as a whole to evaluate the analyzer, calibration, reagent purity, etc. Since the reagents are on the slide and are only opened from the packaging just before use, we can rule out reagent contamination if QC fails.
To Dorothy,
A decrease in lactate points to an improved lactate utilization, such as in the use of a combined clofibrate-biguanide treatment for selected diabetic patients. (Recall: diabetics have a high lactate level due to metabolic acidosis). I haven’t come across such a case though.
Incubation allows for both chemical reactions to take place completely and the measurement of absorbance. The incubation temperature is 37 degrees C.
Hello kent,
Having been to this workstation before, i realise that ammonia samples are also sent in ice. Why is this so? And why lipase, lithium and cholinesterase samples no need sent in ice? Thanks. Cya tml
Ci Liang
TG01
Heyy people,
Here are the remaining answers for those who have been waiting patiently!
To Sally,
Lactate tests are usually ordered as a sole test. It is usually used as a confirmatory test to evaluate acid-base balance, the primary method being ABG (Arterial blood gases- pO2, pCO2, etc). However, lactate tests can be used to monitor a seriously sick patient together with other panel tests, in such case they will provide another sample in a serum-separating tube (gold-capped) for serum chemistry measurement.
Lactate tests may even be done with tests of other disciplines. Its all up to the doctor. We as lab technologists just perform the test! =P
To Randall,
That’s an interesting question. Usually we do not order for fresh samples in such situations. This is because the ice bag is double-bagged and some water will remain in the sample bag even though one might be leaky.
The ice may have melted but as long as the water that remains with the tube is cold, we will continue doing the test. In such situations, we will report the results with a comment, “sample not sent in ice”.
To (unidentified),
Erm.. actually, I do remember saying in my posting that I will cover only on the lactate test? But since you asked, I’ll briefly touch on the other 3 chemistries.
Lithium is used in the treatment of bipolar (manic-depressive) illness. Lithium measurements are used to monitor patient compliance and therapy and to diagnose potential overdose. Symptoms of lithium intoxication include sluggishness, drowsiness, muscle weakness, and ataxia.
Ammonia is a waste product of protein catabolism; it is potentially toxic to the central nervous system. Increased plasma ammonia may be indicative of hepatic encephalopathy, hepatic coma in terminal stages of liver cirrhosis, hepatic failure, acute and subacute liver necrosis, and Reye’s syndrome. Hyperammonemia may also be found with increasing dietary protein intake.
There are two types of cholinesterase. First, Acetylcholinesterase, which is found in red blood cells and nerve tissues. Next, Cholinesterase, which is found in plasma, liver, heart, and other tissues. These measurements are useful in the diagnosis of pesticide poisoning, liver diseases and sensitivity to succinylcholine administration.
Btw, please identify yourself!
To Ci Liang,
Lipase and cholinesterase are enzymes and are resistant to metabolic processes. Lithium ions are stable too. However, ammonia and lactate are actually able to metabolized into other metabolites. For example, lactate into pyruvate. Hence, both lactate and ammonia have to be sent in ice to inhibit the metabolic enzymes from degrading these products.
Samples for lactate and ammonia are sent in EDTA-tubes for the same purpose- to prevent metabolism by inhibiting clotting mechanisms. (yes, clotting mechanisms also assist in metabolism of these substances). Similar to the above scenario, lithium, lipase and cholinesterase can be sent in a plain tube as they are enzymes and are resistant to clotting factor metabolism.
Do feel free to clarify if still in doubt. Thanks!
Hey hey!
Just want to ask, why can QC be done only once a day unlike the other analyzers in the lab?
Take care!
Charmaine Tan
TG01
Hi Charmaine,
Hm.. This qn sounds familiar. Royston had actually asked it in the earlier post, and I've posted a reply.
However, u might also be curious to know why calibration is done only twice a year. The answer is because the immunoassays run on this machine are very stable.
hi kent,
about the QC. the QC is run during each change of reagent or anytime of the day. and is it run automatically or maually.
Lizzie
hello!
i've been to this station as well and its my fave. its straightforward, simple and mess free!
Each chemistry uses a different slide.. and they have to be thawed for 15 mins before use.
why is this so ?
Jo-anne Loh
TG02
To Lizzie,
Before, I explain, I would like to re-emphasize that the slides for each of the chemistries are ALL different due to the different reagents at the reagent layer of the multi-layered slide. In addition, EACH slide comes in a separate packaging, and is fit for only one test. Thus, there is no reagents packs involved.
QC is run at the start of the day in the morning using pre-prepared controls (pooled serum). Like patient’s samples, we will spot a drop of control onto each type of slide (lactate, ammonia, cholinesterase, lipase, etc). The results are checked with the control limits provided to us. If not within control limits, the affected chemisty’s control is re-run.
To Joanne,
I think the slides are the coolest part of this station, though it doesn’t seem environmentally-friendly! =)
As mentioned to Lizzie, the slides for each of the chemistries are different due to the different reagents at the reagent layer of the multi-layered slide. Different reactions, different reagents. As for the need for thawing, the immunoassay reaction and photometric absorbance measurement only take place at 37 degrees C in the analyzer. Thus, it is absolutely necessary to warm up the slide (after retrieval from refrigerator storage) to prevent possible machine errors or inaccuracy of test results.
Hope these answers clarify your doubts! =)
OMG. The unidentified is me. hees. Jiaxin, TG01.
Post a Comment