normal when a person is spilling a lot of sugar in the urine, and even- tuaUy lower than normal when the kidneys have been damaged by years of elevated blood sugars.
It is not surprising to seean appropri ate drop in creatinine clearance when blood sugars are normalized and urine glucose vanishes.
The creatinine clearance test requires a 24-hour urine coUection, and your doctor wiU drawa smaU amount of bloodto measure serum creatinine.The most common causeof abnormaUy lowvaluesfor this test is failure of the patient to coUect aU the urine produced in a 24-hour period.Therefore, if other kidneytests are normal, testswith low values for creatinine clearanceshould be repeated for verification.
A low creatinine clearancewithout excess urinary protein suggests a nondiabetic cause of kidney impairment.
When it is impractical to makea 24-hour urine collection, as for small children, a new test requiring a smaU amount of blood, crystatin-c, can be performed.
Crystatin-c is beUeved to be a more accurate mea sure of kidney function than creatinine clearance, but unfortunately many insurers still consider this test to be "experimental" and won't pay for it.
Serum beta2 microglobulin.
This is a verysensitive test for injury to the tubules ofthe kidneys,which pass urine filtered from the blood.
As with fibrinogen levels, elevatedvaluescan also result from inflam mation or infection anywhere in the body.
Thus an isolated elevation of serum beta2 microglobulin without the presence of urinary kappa Ught chains or microalbumin is probably due to some sort of infec tion, not to diabetic kidney disease.
Such elevation is commonplace in people with AIDS, lymphoma, and immunodeficiency disorders.
24-hour urinary glucose. This test too requires a 24-hour coUection 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.
Tests: Baseline Measures 61
As indicated under "Cardiac Risk Factors," significant kidney dam age is also accompanied by elevations of serum homocysteine and fi brinogen.
OTHER TESTS
Insulin-like Growth Factor 1 (IGF-1) Rapid correction of veryhighbloodsugars can,on occasion, cause ex acerbation of a common compUcation of diabetes caUed proliferative retinopathy.
This condition cancause hemorrhaging inside theeye and blindness.
Such exacerbations are usuaUy preceded by an increase in serumlevels of insulin-like growth factor 1.Abaseline level of IGF-1 in theblood should bemeasured in people with proliferative retinopathy.
Repeat determinations shouldbe made every two to three months.
If levels increase, bloodsugars should thenbe reduced moreslowly.
R-R Interval Study The purpose of this studyis to test the functioning of the vagus nerve, and it should be part of your initial diabeticphysical examination.
It is performed like an ordinary electrocardiogram, but it requires fewer electrical leads (i.e.,only on the limbs, not the chest).
The vagus nerve is the largest nerve in the body, running from the brain to the lower body.
It's the main neural component of the parasympathetic nervous system, or that part of the nervous system that takes care of vegetative, or autonomic, functions, the functions that run more or less on "automatic pilot" and which you don't ac tively have to think about to make happen.
These include heart rate and digestion.
Like any other nerve in the body, the vagus nerve can be injured by long-termexposure to highbloodsugars, but since it plays sucha cen tral role in bodily function, damage to it can cause many more disor ders than damage to most other individual nerves.
The vagusplaysa major role in a number of diabeticcompUcations involving the autonomic nervous system, including rapid heart rate, erectile dysfunction in men, and digestive problems,particularly gas- troparesis, or delayed stomach-emptying (which we wiU discuss in de tail in Chapter 22).
The good news is that when you'vehad your blood sugars normalized over an extended period, it can slowly recover
62 Before You Start
proper function. (Many ofmy male patients who have been unable to achieve or maintain an erection report that after blood sugars have been normalized,that abiUty has returned.) This nerve is unique in that its function canbe investigated simply and cheaply.
If thevagus nerve isworking properly, there should be a considerable difference in heart rate between inhaling and exhaling.
By measuring thevariation ofyour heart rate with deep breathing, we canget a picture ofjusthow much thefunction has been impaired.
In nondiabetics, the heart rate increases when they inhale deeply and slows when theyexhale fully.
So a twenty-one-year-old nondiabetic's heart ratemight typicaUy slow asmuch as75 percent from inhaling to exhaling.
This may drop to about 30 percent for a seventy-year-old nondiabetic.
Ayoung type 1diabetic withtenyears ofvery highblood sugars maynot have anyheart rate variation at aU. (Thevariation is measured by lookingat the interval between "R-points," or peaks on the tracing of the electrocardiogram.
As you're probablyaware, each time your heart beats, the electrocardiograph traces a shape resem blinga mountain.Thetip of the mountainisthe R-point, sothe physi cian measures the intervals between R-points.) I consider this test an important, reproducible, quantitative mea sure of an important diabetic compUcation and perform it on aU of my new patients beforeblood sugars have been stabUized.
I repeat it about everyeighteen months, for several reasons.
It's a very good in dex of how,with aggressive blood sugar control, neurologic compUca tions can and do reverse, and it gives both patient and doctor good, concrete evidence of the success of treatment, and encouragement to keep it up.
Additionally, the digestive disorder of gastroparesis, which I mentioned above, can be and frequently is one of the most difficult barriers to blood sugarnormalization, and can evenmakeblood sugar control virtuaUyimpossiblein some people who require insulin.
A low heart rate variabiUtyon the initial test can be a good indicator that the patient is likely to have a problemwith delayed stomach-emptying.
It can alsogive the doctor clues as to causes of other problemsthat a pa tient maybe experiencing , sexual dysfunction, faintingupon stand ing when arising from bed, and so on.
Neurologic Examination In addition to a standard physical examination,it is desirable (but not essential) that a routine neurologic exam be performed before blood sugars are corrected, and again everyfew years thereafter. These tests
Tests: BaselineMeasures 63
arenot painful. They should include checking forsensation in thefeet, reflexes oflimbs and eyes, short-term memory, and muscle strength. In my experience, performance on a number of the neurologic tests improves after many months of essentiaUy normal blood sugars. Per formance tends to deteriorate ifblood sugars remain high.
Eye Examination One of the most valuable retinal studies, the Amsler grid test,can be performedby anyphysician or nurse in less than a minute without di lating your pupUs. Since chronicaUy high blood sugars frequently cause a number of disorders that can impairvision, your eyes, if nor mal, shouldbe examined carefuUy byan ophthalmologist every oneto two years. The ophthalmologist wiU evaluate the retina, lens, and anterior chamber in each eye, and you can expect to have your pupils dilated with special drops.A proper retinalexamrequires the use of both di rect and indirect ophthalmoscopes and a sUt lamp.If an abnormaUty is found, certainexaminations mayhave to be performedby a retinol- ogist every few months.
Examination of the Feet Because ulcers of the diabetic foot are avoidable, even when blood sugar is not weU controUed, you should askyour physicianto examine your feet at every routine office visit. Foot problems that aren't pre vented or treated properly can lead to serious compUcations, even am putation. Your physician should train you in foot self-examination and preventive care. In Appendix D, I have reproduced the same in structions I give my own patients on how to care for their feet.
Oscillometric Study of Lower Extremities This inexpensive test utilizes a simple blood pressure cuff connected to a small instrument that should be in everydoctor's office.It givesan index of the adequacy ofpulsatilecirculation to the legsand feet.Since long-standing, poorly controUed diabetes can seriously impair pe ripheral circulation, this test is fairly important.
AU diabetics should take special care of their feet, but if you have an abnormal osciUomet- ric study, you have to be extra careful.
People who have diminished circulation in the legs usuaUy also have significant deposits in the ar teries that nourish the heart and brain and the arteries necessary for penile erection.
Therefore, if this study shows impaired circulation,
64 Before You Start
your doctor may want you to undergo tests thatwould help diagnose coronary artery disease and, if you have certain symptoms, diagnose impaired circulation to the brain. OsciUometry canbe performed by anytrainedphysician in but a few minutes. It is taughtat manymed ical schools throughout the world but rarely in the United States, where hands-on care is diminishing.
Musculoskeletal Examination Prolonged high blood sugars can cause glycation of tendons.
Glyca tion is the permanent fusing of glucose to proteins, and the simplest analogy is bread crust.
Think of the soft inside of the bread as your tendons as they should be,and the crust aswhat happens when they're exposedto elevated blood sugars overa long period of time.
Glycation of tendons occurs in such common diabetic complications as Du- puytren's contractures of the fingers, frozen shoulders, triggerfingers, carpal tunnel syndrome, and iliotibial band/tensor fascialata syn drome of the hips and upper legs.
All of these conditions are easily treated if caught early and blood sugars are controUed.
A muscu loskeletal examination can identify these in their early, treatable stages.*
When to Perform These Tests As valuable as they can be to you and your physician, none of the abovetests is crucial to our central goal of achieving blood sugar nor malization.
If you are without medicalinsurance, or if your insurance won't pay for these tests,and financial considerations are a top prior ity, aU can be deferred.
If, however, you are experiencing problems, such as impairment of vision, you should be tested immediately.
Also, examination of your feet, and learninghow to care for them properly, is vital and can prevent or forestall serious problems.
The most valuable of these tests for our purposes is the HgbAlc, because it alerts your physician to the possibility that your self- monitored blood sugardata maynot reflect the average blood sugarfor the prior three months.
This can occur if your blood sugar-measuring technique or supplies are defective.
More commonly, some patients, with a scheduled visit to the doctor approaching, wiU improve their
For information on the proper treatment of these conditions, visit www. diabetes-book.com; select"Articles" and then the article tide that begins "Some Long-TermSequelaeof PoorlyControlled Diabetes."