Re: Good info re: avoiding falsely elevated potassium results in the lab setting

[Guest guest]

I belive that many that draw blood don't do it right. Don't know if it is poor

training or they forget what they learned.

On sat. I went to ED for an infection. the ED nurse and Dr tried to draw my

blood between the two of them it took 5 tries before getting blood.

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> My husband gets such grief when he asks the lab tech to release the tourniquet

before drawing the K and he always has to explain why he shouldn't make a fist

during the draw...shouldn't they know this??

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http://www.bd.com/vacutainer/pdfs/VS7048_troubleshooting_erroneous_potassiums_po\

ster.pdf

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[Guest guest]

Yes the should. He should complain to the lab supervisor and maybe take a copy of one of our papers in our files on this issue.CE Grim MDMy husband gets such grief when he asks the lab tech to release the tourniquet before drawing the K and he always has to explain why he shouldn't make a fist during the draw...shouldn't they know this??http://www.bd.com/vacutainer/pdfs/VS7048_troubleshooting_erroneous_potassiums_poster.pdf

[Guest guest]

Paramedics also draw blood for K not sure how well they are trained for this. I

think many don't do the order of draw right.

Since I am hard to get blood from I don't think any one has done it right on me.

Ed likes to try getting blood from my hands so this means they use smaller

needle.

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> > My husband gets such grief when he asks the lab tech to release the

tourniquet before drawing the K and he always has to explain why he shouldn't

make a fist during the draw...shouldn't they know this??

> >

> >

http://www.bd.com/vacutainer/pdfs/VS7048_troubleshooting_erroneous_potassiums_po\

ster.pdf

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>

[Guest guest]

I have had my B/P taking a few times where the cuff comes partly undone and the

nurse holds it in place. Easier to do this then use right size cuff.

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> > > > My husband gets such grief when he asks the lab tech to release

> > the tourniquet before drawing the K and he always has to explain why

> > he shouldn't make a fist during the draw...shouldn't they know this??

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http://www.bd.com/vacutainer/pdfs/VS7048_troubleshooting_erroneous_potassiums_po\

ster.pdf

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[Guest guest]

How about taking B/P over a Shirt sleeve? This is very commonly done.

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> >> > > My husband gets such grief when he asks the lab tech to release

> >> the tourniquet before drawing the K and he always has to explain

> >> why he shouldn't make a fist during the draw...shouldn't they know

> >> this??

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> >> > >

http://www.bd.com/vacutainer/pdfs/VS7048_troubleshooting_erroneous_potassiums_po\

ster.pdf

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[Guest guest]

Uesing small needles causes something called Hemolysis. may be the reason you

have never had low K show up in your tests.

Hemolysis of red blood cells releases large amounts of potassium into the

surrounding plasma. Erythrocytes contain 23 times as much potassium as the

plasma. The most common causes for hemolysis are related to mechanical factors

during the collection process:

Use of a syringe with excessive suction applied to the plunger is by far the

most common cause of hemolysis, with almost 80% of hemolyzed

samples associated with use of a syringe rather than an evacuated tube for

collection. (2) Nineteen percent of syringe-collected specimens were hemolyzed

in one study, as compared to 3% of specimens that were collected in evacuated

tubes. (3)

Forcibly squirting the blood from a syringe into an evacuated tube causes shear

forces on the red cell membrane, resulting in rupture of the cell. (4) Evacuated

tubes should be allowed to fill slowly from the vacuum in the tube, without

pressing on the syringe plunger.

Drawing the blood through a small needle or catheter also ruptures red cells as

they pass through either. The narrower the needle or catheter, the greater is

the hemolysis. (5,6) Blood collected with a 23-gauge needle has higher potassium

concentrations than blood from the same individual collected with a 19-gauge

needle. (6) The hemolysis rate is inversely proportional to the diameter of the

needle or catheter, with the highest hemolysis rates in 24- to 20-gauge

catheters. (5)

Using a large-diameter needle that causes the blood to enter the evacuated tube

with great force also can rupture red cells. Becton-Dickinson recommends using a

special low-vacuum evacuated tube in this situation.

Drawing the blood through an IV tube or catheter where the diameters of the

catheter, tube adapter device, and cap-piercing needle are mismatched can cause

turbulence of the blood, with cell rupture.

Inverting the tube too vigorously to mix the blood with anticoagulant also

causes turbulence.

Some authors have listed prolonged application of a tourniquet as a cause of

hemolysis, or elevation of the potassium without hemolysis. Statland (7) studied

the effect of tourniquet application for three minutes and found no significant

change in potassium concentrations. Likewise, in Don's study of fist clenching,

(8) tourniquet application for three minutes without fist clenching had no

effect on the potassium.

Because the major cause for hemolysis is the use of a syringe rather than an

evacuated tube system for blood drawing, it is mostly a problem in areas where

blood is drawn by non-laboratory personnel, such as in emergency departments and

ICUs. It tends, therefore, to be seen in clusters. It is reasonable to expect a

hemolysis rate of less than 2%. (2,4)

But are we, unknowingly, likely to test a hemolyzed sample? And if it is

hemolyzed, is it going to raise the potassium very much? Several studies have

shown that hemolyzed serum or plasma containing 1 gram/Liter of hemoglobin will

have an increase of .27 mmol/L to .33 mmol/L potassium. (9,10,11,12,13) In one

study in which 100 patients were examined, the K:Hgb ratio was very variable,

ranging from .20 to .35. It is not possible to correct the potassium of

hemolyzed blood by applying a correction factor. Other cellular constituents,

such as lactrate dehydrogenase, ALT, AST, and CK are also increased. Figure 1

relates the appearance of the hemolyzed serum to the resulting elevation of

potassium.

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> > > My husband gets such grief when he asks the lab tech to release the

> >tourniquet before drawing the K and he always has to explain why he shouldn't

> >make a fist during the draw...shouldn't they know this??

> > >

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>http://www.bd.com/vacutainer/pdfs/VS7048_troubleshooting_erroneous_potassiums_p\

oster.pdf

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