A BASELINE MEASURE OF YOUR DISEASE
AND RISK PROFILE
Part 3
Excerpted from Chapter 2: TESTS
Continued:
Renal
Risk Profile
Chronic blood sugar elevation for many years can cause slow deterioration
of the kidneys. If caught early, it may be reversible by blood sugar
normalization, as it was in my own case. Unless you think frequent hospital
visits for dialysis might be a nice way to meet people, it’s wise
to have periodic tests that reflect early kidney changes. It is also
wise to have all these periodically performed together, as the results
of each can clarify the interpretation of all.
Several factors cause false positive results in some of these tests,
so you should keep them in mind when your doctor schedules the tests.
You should avoid strenuous or prolonged lower-body exercise (which would
include motorcycle or horseback riding) in the 48 hours preceding the
tests. Additionally, if on the day the tests are to be performed
you are menstruating or have a fever, a urinary tract infection, or
active kidney stones, you should postpone the tests until these conditions
have cleared.
A basic renal risk profile should include the following:
Urinary kappa light chains
If early diabetic kidney disease is present, this test reports “polyclonal
kappa light chains present.” This means that small amounts of
tiny protein molecules may be entering
the urine, due to leaky blood vessels in the kidneys. Because these
molecules are so small, they are the first proteins to leak through
tiny pores in the blood vessels of the kidneys that may have been affected
by disease.
This test requires a small amount of fresh urine. If the test report
states “monoclonal light chains present,” there is a possibility
of treatable malignancies of certain white blood cells.
Microalbuminuria
This less costly test can now be performed qualitatively (by dipstick)
in your doctor’s office, or quantitatively at outside laboratories.
It, like the urinary kappa light chain test, can also reflect leaky
vessels in the kidneys, but at a later stage, since albumin is a slightly
larger molecule.
A quantitative measurement requires a 24-hour urine specimen, which
means you’ll need to collect all the urine you produce in a 24-hour
period in a big jug and deliver it to your physician or laboratory.
Given the potential embarrassment of carrying a jug full of urine around
at work, you might want to schedule your test on a Monday and collect
the urine while at home on Sunday. Many of my women patients report
that it’s easier to collect urine initially in a clean paper cup,
and then pour it into the jug. An easier screening test is the measurement
of the albumin-to-creatinine ratio in a first morning urine sample.
24-hour urinary protein
This test detects kidney damage at a later stage than the preceding
two tests; it also requires a 24-hour urine collection. As with the
other tests, false positive results can occur following strenuous lower-body
exercise, as previously noted.
Creatinine clearance
Creatinine is a chemical by-product of muscle metabolism, and is present
in your bloodstream all the time. Measuring the clearance of creatinine
from the body is a way of estimating the filtering capacity of the kidneys.
Test values are usually higher than normal when a person is spilling
a lot of sugar in the urine, and eventually lower than normal when the
kidneys have been damaged by years of elevated blood sugars. It is not
surprising to see an appropriate drop in creatinine clearance when blood
sugars are normalized and urine glucose vanishes.
The creatinine clearance test requires a 24-hour urine collection,
and your doctor will draw a small amount of blood to measure serum creatinine.
The most common cause of abnormally low values for this test is failure
of the patient to collect all the urine produced in a 24-hour period.
Therefore, if other kidney tests are normal, tests with low values for
creatinine clearance should be repeated for verification.
A low creatinine clearance without excess urinary protein signifies
a nondiabetic cause of kidney impairment. When it is impractical to
make a 24-hour urine collection, as for small children, a new test requiring
a small amount of blood, crystatin-c, can be performed.
Serum beta2 microglobulin
This is a very sensitive test for injury to the tubules of the kidneys,
which pass urine filtered from the blood. As with fibrinogen levels,
elevated values can also result from inflammation or infection anywhere
in the body. Thus an isolated elevation of serum beta2 microglobulin
without the presence of urinary kappa light chains or microalbumin is
probably due to some sort of infection, not to diabetic kidney disease.
Such elevation is commonplace in people with AIDS.
24-hour urinary glucose
This test too requires a 24-hour collection of urine, and is of value
for proper interpretation of the creatinine clearance.
Note: If, as you’ve been reading about these tests, you’ve
imagined yourself lugging around multiple jugs of urine, most of us
only need one 3-liter jug. This should give you an adequate specimen
for your physician to perform creatinine clearance, microalbumin, 24-hour
protein, and 24-hour glucose. Nevertheless, it’s wise to bring
home two empty jugs, just in case your urine output is very high.
As indicated under “Cardiac Risk Factors,” significant kidney
damage is also accompanied by elevations of serum homocysteine and fibrinogen.
Part 4 Tests Continued
Part One,
Part Two,
Part Four
We would like to thank the publisher Little Brown and Company and
Dr. Richard K. Bernstein, for allowing us to provide excerpts from Diabetes
Solution.
Copyright © 2003 by Richard K. Bernstein, M.D.
All rights reserved. No part of this book may be reproduced in any form
or by any electronic or mechanical means, including information storage
and retrievalsystems, without permission in writing from the publisher,
except by a reviewer who may quote brief passages in a review.
Author’s Note
This book is not intended as a substitute for professional medical care.
The reader should regularly consult a physician for all health-related
problems and routine care.
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