Ask the Doctor

Ask the Doctor

ASK THE DOCTOR

by Wesley W. Wilson, MD

Artwork: Medical caduceus

NOTE: If you have any questions for "Ask the

Doctor," please send them to the VOICE editorial office. The only questions Dr.

Wilson will be able to answer are the ones used in this column.

Wesley W. Wilson, MD, has retired as an Internal

Medicine practitioner at the Western Montana Clinic in Missoula, Montana. Dr. Wilson was

diagnosed with type 1 diabetes in 1956, during his second year of medical school. He

remains interested and involved in diabetes education for patients and professionals.

Q: I've had diabetes for years now, and all that

jabbing of my fingers (for the blood tests) is making them go numb. Is there another place

I can use to get an adequate blood sample?

A: I have some concerns about your numb fingers.

Are you sure it's from the testing? Persons with diabetes can develop problems with nerve

function, that can cause numb fingers. Are all the fingers numb, or just the ones you use

to take blood samples? Any numbness of the toes? Has your doctor evaluated this problem? A

simple test of nerve function in the toes is the monofilament test, and that test can be

carried out by patients themselves. Information about this test can be found in

"Diabetes Forecast," or by calling the American Diabetes Association. Could this

numbness be a manifestation of Carpal Tunnel Syndrome? It seems important to decide what

is causing the numbness.

Despite my uncertainty as to the cause of your

numb fingers, I also have concerns about using the fingers for testing. Certainly, I've

seen persons who test a lot with rough, callused, and scarred fingers. Not only are there

more sensory nerves in the fingers than in most other parts of the body, but the fingers

are certainly more in contact with the environment than are most other parts of the body.

As I am a physician frequently in contact with persons who may have infectious diseases, I

have concerns about any penetration of the protective barrier the skin provides. Careful

hand-washing and glove use can minimize exposure to infections such as hepatitis or HIV,

but it has seemed prudent to further minimize exposure where possible.

I have used the area just above the knee for

blood sampling for years. It is much less painful than the finger, and appears to be

accurate. About five years ago, I decided to test that assumption.

I ran an experiment to see if blood tests from

the knee area were as accurate as those taken from the finger. My experiment consisted of

40 blood sugar tests, done in triplicate. Each test consisted of a sample taken from the

area just above the knee, another sample taken from a finger, and then, within ten

minutes, a venous blood sample from which a plasma glucose was done in the Western Montana

Clinic's clinical laboratory. I wished to compare the accuracy of the knee sample with

that of the finger-stick sample, and I used the laboratory as the referent, a "gold

standard." The results showed excellent agreement between the knee and finger, and

both knee and finger compared closely with laboratory (venous blood) results. The area

just above the knee is an accurate, painless site for blood sugar testing.

There are some problems with knee testing. Women

seem to have more trouble than men getting an accurate sample. Skinny persons such as I am

can get a fold of skin to squeeze it to milk a drop of blood to the surface easier than

can persons whose skin is more tightly filled. Some meters do not allow the tester to

invert the meter over the puncture site and touch the reaction pad to the drop of blood.

I've had excellent results with the Precision QID and the AccuChek Advantage (using its

Comfort Curve test strips).

As an inconvenience, there is sometimes the

tendency for a bit of blood to ooze, after the test, and this may stain the knee of your

trousers.

Blood sampling from above the knee can provide an

accurate and painless alternative to finger-stick blood glucose monitoring.