Monday, August 6, 2007

 

Clincal Chemistry

Yo. It's just 14 weeks to go to the end of SIP. 14 weeks! I will be describing the blood ketones tests here.

Blood Ketones Test

Blood ketones are tested using the Optium Xceed handheld meter. The basis for this meter is electrochemical. This is a very easy gadget to use. First, a new test strip is inserted into the strip-port. An ‘apply blood’ (it shows a blinking drop) icon will show. Then, apply 1 drop of blood onto the other end of the test strip. Wait for about 30 seconds and the results will be shown on the screen. However, it must be ensured that the blood samples are sent in lithuim heparin tubes (green cap). The heparin acts as an anticoagulant. Blood delivered in any other types of blood tubes are rejected. The reference range for this test is 0.0 – 0.6 mmol/L. Critical values (> 1.4 mmol/L) must be reported immediately to the appropriate personnel, so that action can be taken by the doctor to treat the patient.

Calibration is done for every new box of test strips by inserting a CODE key into the strip-port to check for the correct CODE number.

Controls are done only when there are requests for blood ketones, mainly because there are very few requests for blood ketones (about 1 a day). There are 2 levels of controls; one of a low value and the other high. Only 1 level of control is done when there is a blood ketone test, and the controls are tested alternatively (i.e. one day use control of high value, the next time use the control of low value).

Blood ketone testing is usually done on patients with diabetes. In diabetes, there is not enough insulin or insulin activity to help the muscles to absorb glucose from the blood. When there is not enough glucose, the body will burn fat for energy. Breakdown products, or ketones, are formed. Ketones are toxic to the body. Accumulation of these acids in the body may lead to ketosis. A more serious disease is known as ketoacidosis or DKA.

Why use blood and not urine for measurement?
There are 3 types of ketone bodies – acetone, acetoacetate and β-hydroxybutyrate. β-hydroxybutyrate makes up 75% of all ketones in DKA. Therefore, it is more relevant to measure β-hydroxybutyrate in blood rather than urine ketone tests based on the nitroprusside reaction which detects acetoacetate instead. Urine ketone tests also give false positive results in the presence of some drugs and false negative results when the test strips are exposed to air for too long.

That's it for now.

Martin Ng (TG02)

0503312A


Comments:
Hi Martin!

What types of drugs gives false posititve results? and why exposing
test strips for too long will give false negative results? Thanks =)

Eugene Wong
TG02
 
Yo martin

Having been to this workstation before,i found that ketone testing is done using whole blood. Why can't we use serum/plasma? Thanks cya tml

Ci Liang
TG01
 
hi martin!
erm may i know is there an expiry date for the calibration?
What happens if the calibration expires before the reagent is used up?

Natalie
TG01
 
Yo,

Could you elaborate on the principle of the ketone test? Thanks.

Yong Yang
TG02
 
yo martin

when you say the basis for the optium Xceed meter is electrochemical? Can you elaborate more on electrochemical?

Thanks,
Randall
TG02
 
hello martin :)

why is it that only lithium heparin tube can be used? by using other anti-coagulant affects the results or the process?

phuiyuen
 
hey.. juz wondering.. Are there (or wad are the) consequences that would bring the patient if he or she had ketoacidosis?

Jia Hao
 
Hi Eugene

Drugs containing sulphydryl groups will give false results. The urine test strips will deteriorate with exposure to air, so it will give false negative results.

Hi Ci Liang

The blood ketone test strip is not designed for use with serum, plasma, arterial or neonatal blood samples.

Hi Natalie

As far as i know, there is no expiration date for calibration. Every new box of strips has a calibration strip and is used for calibration.

Hi Yong Yang and Randall

I believe that both of you are asking the same question. The blood sample will react with chemicals in the test strip, producing a small electrical current. The amount of current is proportional to the amount of β-hydroxybutyrate in the blood sample.
 
hello.

if a person is diagnosed with DKA, how can the patient be treated?

Joanne Loh
TG02
 
Hi Phui Yuen,

Only lithium-heparin tubes can be used because heparin prevents further breakdown of ketones into other products. If other tubes are used, the true value of ketones will not be measured. This would also mean that ketone specimens are usually sent in ice and immediately done upon receiving the sample.

Hi Jia Hao,

Some of the consequences include emobolism, hyperglycemia, myocardial infarction due to disseminated vascular coagulation.
 
Hi Joanne,

Treatment of ketoacidosis will include infusion of insulin (for diabetes), and infusion of dextrose saline for electrolyte balance, especially potassium.
 
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