Glycemic Control and Longitudinal Testing for Exercise Microalbuminuria in Subjects with Type I Diabetes

Satish K. Garg, MD

H. Peter Chase, MD

Sherrie Harris, BSN

Guillermo Marshall

Sandy Hoops, CHA

Iris Osberg, BS

Department of Pediatrics, Barbara Davis Center for

Childhood Diabetes, University of Colorado

Health Sciences Center, Denver, Colorado

Reprint requests to: Satish K. Garg, MD, Department of Pediatrics, Barbara Davis Center for Childhood Diabetes, University of Colorado Health Sciences Center, 4200 E. Ninth Ave. Box B140, Denver, CO 80262. Submitted for publication March 1990, ac- cepted in revised form June 1990.

0 1990 Elsevler Science Publishing Co., Inc. 0691-6632190/$3.50

154

ABSTRACT

There is a need fqr better and earlier markers of clinical renal damage in subjects with Type I diabetes. In this prospective study, exercise albumin excretion rates (AERs) were studied longitudinally for a 4- year period in 187 young subjects with Type I diabetes. For this time period, 54% of subjects continued to have normal overnight and ex- ercise AERs, 11% had continuously elevated exercise and overnight AERs, 11% developed an elevated exercise AER with the overnight AER remaining normal, and 12% had a normal overnight AER through- out the study, with initially elevated exercise levels later decreasing to normal. This improvement in exercise AER was associated with improved glycosylated hemoglobin (HbA,) values for 84% of the sub- jects (p = 0.0004, paired t test). Five percent of subjects, who initially had only an elevated exercise AER, developed a consistently ele- vated overnight AER. Seven of these nine subjects showed either worsening (>lO%) or no improvement in their HbA, values from the initial to the final study periods. Five percent of subjects continued to have an elevated exercise and normal overnight AER throughout the study. These results show that the elevated exercise AER rep- resents a definite transitional stage between a normal and an ab- normal (>30 pg/min) overnight AER. In addition, a “window” exists during which an elevated exercise AER may be reversed by improved glucose control, but if this improvement does not occur, progression to an increased overnight AER is likely to result. (The Journal of Di- abetic Complications 4;4:154-158, 1990.)

INTRODUCTION Diabetic nephropathy occurs in 30-40% of subjects with insulin-de- pendent diabetes mellitus (IDDM, Type I), with a peak incidence after 16 years of disease.“’ An albumin excretion rate (AER) persistently above 30 pg/min is associated with eventual development of diabetic nephropathy.3-6 Unfortunately, when this level of overnight microal- buminuria is detected, it may already be too late to reverse the process. Thus, tests that might be predictive of an even earlier stage of kidney damage are needed.

Most studies have determined AERs under basal, unstressed con- ditions.3,7-‘0 Minimal glomerular pathology, as seen on kidney biop- sies,” may need some provocative stimulus to unmask the underlying pathology. Recently, exercise has been suggested to provoke microal- buminuria that is detectable under basal conditions.‘2-‘4 Longitudinal studies of exercise AERs are not yet available, however. Similarly, the relationship of exercise to overnight AERs and to longitudinal glycemic control have not been studied.

The present prospective study was designed to determine if post- exercise microalbuminuria is a reliable early marker of an eventually increased overnight AER. To determine this, we undertook longitudinal exercise testing in young subjects with Type I diabetes. The role of glucose control in progression and/or regression of exercise microal- buminuria was also investigated.

EXERCISE MlCROALBUMlNURlA IN IOOM 155

METHODS All subjects followed in our clinic who are between 13-

22 years of age and who have had diabetes 25 years are encouraged to attend the “Eye-Kidney” clinic. As long as their first visit is before age 22, they can then attend an- nually (or more often if needed), with no upper age limit. More than 90% of the total eligible population have at- tended the clinic at least once (406 subjects). Only 187 of the 406 subjects have collected a minimum of one overnight and one exercise urine sample at least 1 year apart for AER determinations, however, and they are the subject of this report. There were no other exclusion cri- teria; five subjects (all in group 2; Table 1) were receiving medications for hypertension, and some subjects in group 2 already had persistent microalbuminuria at the time of entry into the study.

formed the 20-minute exercise test. The 95th percentile of normal for exercise AER for the 41 controls was 41 .O kg/min (range 1.4-41.0 kg/min). The 95th percentile of normal for overnight AER for the 41 controls was 7.6 pg/min (range 0.1-7.6 pglmin).

Overnight collections are obtained as previously de- scribed.16 The exercise consists of 20 minutes of vigorous pedaling on a standard exercise bike without a set level of kpm/min. The standard exercise bicycle was purpose- fully used so that similar testing could be easily done in any physician’s office. For a similar reason, a steady-state water diuresis was not instituted before exercise began. As with the overnight urine testing, the exercise testing is not done during the menstrual cycle or if there is evi- dence of a urinary tract infection (by history: dipstick for white blood cells and urinalysis if indicated). All partic- ipants are asked to empty their bladder before riding the exercise bike. Subjects are then given 500 ml water to drink before the test so that they can void as soon as possible after completing the exercise. The subjects were not followed for further urine collections after the initial postexercise voiding. Blood pressure and pulse are also measured during the exercise testing, and their influence on exercise AER will be the subject of a future report. The clinical data is shown in Table 1. The study protocol was approved by the University Hospital Human Subjects Committee.

Glycosylated hemoglobin (HbA,) levels were measured using affinity column chromatography (Isolab, Quik-Sep Fast Hemoglobin Test System, Akron, OH). Normal values remained the same (6.3-8.2%) throughout the study. For purposes of this study, results were expressed as the mean for all values for each year recorded between July 1979 and November 1989. The mean of all yearly values for 1979-1985 (before the first microalbumin tests), and for 1986-1989 (the follow-up period), were used for anal- yses. Depending on the amount of change (>lO% in HbA, levels), the subject’s glucose control was classified as improved or worsened. If the mean HbA, levels for the two time periods were within lo%, the subjects were clas- sified as “no change.”

Microalbuminuria levels were determined by radioim- munoassay (WA, Albumin Double Antibody Kit; Diagnos- tic Products, Los Angeles, CA): the lower limit of the assay by this method is 0.5 pg/min. Increased overnight and exercise AERs (microalbuminuria) were defined as >30 and >41 kg/min, respectively, on at least two dif- ferent urine samples. The level of >30 (*g/min was used to define abnormal on the overnight urine samples, be- cause this level has been shown to be indicative of even- tual diabetic nephropathy.3 Using this level to define ab- normal results in classifying some subjects who have AER values above the 95th percentile of normal, as nor- mal.

Forty-one age-matched young, healthy, nondiabetic controls also collected overnight urine samples and per-

Statistical Methods The SAS program package was used for all data analyses.” Statistical analyses included the x2 test, paired and two independent sample Student’s t tests, and analysis of variance (ANOVA). Tukey’s mul- tiple comparison analysis’7 was used when a significant difference was found with ANOVA. The Markov model was applied to describe the transition rates.”

TABLE 1 Longitudinal AERs and Demographic Data

Group

1 2 3 4 5 6 7

p Value

AER

Initial Final No. of

Exercise ON Exercise ON Subjects Age (yr)

Gender: M/F (Mean f SEM)

; n + + ---* : f

n 102 49153 20.3 0.3 -c 20 lo/lo 21.3 + 0.6 n 9 415 21.0 * 0.6

n + + n 20 9111 20.0 * 0.6 n + 23 12111 21.6 2 0.6 n + ; : 9 712 18.7 + 0.4

variable - - 4 o/4 19.5 1.2 2 0.306 0.115

Duration of IDDM (yr)

(Mean f SEM)

11.9 f 0.4 14.8 f 0.9 11.2 2 1.2 13.0 2 1.0 13.3 ‘- 0.8 13.0 2 0.8 14.3 2 2.6

0.042’ (x2 test) (ANOVA) (AN&A)

AER, albumin excretion rates; IDDM, insulin-dependent diabetes mellitus; ON, overnight; n normal (~30 pg/min for ON AER and 541 pg/min for exercise AER); ANOVA, analysis of variance. + = increased.

l Only groups 1 and 2 were significantly different by Tukey’s correction for multiple comparisons.

GARG ETAL.

TABLE 2 Overnight and Exercise AER

AER (Geometric Mean f 1SEM)

Exercise’ Overnight*

Group Initial Final initial Final

1 8.0 + 0.4 10.0 f 0.8 2

5.5 * 0.3 5.8 f 399.0

0.2 f 111.7 582.9 f 203.8 230.4 k

3 58.9 315.1 f

82.1 88.2

2 13.8 83.1 k 21.8 9.3 f 4

1.8 9.8 + 15.0

2.8 k 3.2 84.7 ‘-’ 22.8 7.2 f

5 0.9 10.1 k 1.1

83.4 ‘- 9.3 13.4 k 2.2 8.5 2 6

1.1 6.8 f 52.7

0.9 2 24.5 155.5 -+ 48.1 19.0 ‘- 5.1

7 51.2 f

72.7 17.9

k 66.1 36.9 f 40.3 9.0 2 2.3 10.80 f 8.9

Values expressed in micrograms per minute. The groups and number of subjects are the same as in Table 1. l Values are the geometric mean of the mean values for each subject for initial (1986-1987) and final (1988-1989) determinations.

RESULTS

Six hundred and eight post exercise urine samples were collected longitudinally from 187 subjects with Type I di- abetes. Similarly, 638 overnight urine collections for AER determinations were collected for 4 years (1986-1989) from the same 187 subjects. The subjects were divided into seven groups, depending on the results of their ex- ercise and overnight AER values (Table 1). The mean age and gender distribution were not significantly different between the seven groups (Table l), and duration of di- abetes was only significantly different between groups 1 and 2, using ANOVA and Tukey’s correction for multiple comparisons.

One hundred-two subjects (54%; group 1) had normal exercise and overnight AERs throughout the 4-year study period (Table 2). in contrast, 20 subjects (11%; group 2) had elevated exercise and overnight values throughout the study, and 9 subjects (5%; group 3) had elevated ex- ercise and normal overnight values initially and on follow- up, whereas 20 subjects (11%; group 4) changed from having normal values for both exercise and overnight AER, to having an elevated exercise value with the over- night value remaining normal. Twenty-three subjects (12%; group 5) initially had an elevated exercise and nor- mal overnight AER but later improved, with both values becoming normal. Nine subjects (5%; group 6) pro- gressed from having elevated exercise and normal over- night values to having increased exercise and overnight

AERs. Four subjects (2%; group 7) had variable AERs for overnight and exercise collections and could not be clas- sified in any of the above groups.

The mean HbA, value for all years before 1986 (time of initial testing) was compared with a mean value for 1986 through 1989 (follow-up testing; Table 3). Mean HbA, val- ues were significantly different between the seven groups (global ANOVA) on both initial (1979-1985), and follow- up (1986-1989) testing (Table 3). Mean HbA, values be- fore 1986 were significantly higher only for groups 2 and 4 as compared with group 1 (ANOVA using Tukey’s cor- rection for multiple comparisons). In contrast, there were no significant differences in mean HbA, values between individual groups for the 1986-1989 period. Mean HbA, values decreased significantly (p = 0.004-0.0004; paired t test) from the initial to the follow-up period for groups 2, 4, and 5.

Fourteen of the 22 subjects in group 5 (64%) showed improvement in their mean HbA, values by ~10% (Table 4), but mean HbA, values improved for only two of the nine subjects (22%) in group 6 who developed overnight microalbuminuria on follow-up.

Markov’s model, applied to all subjects with normal overnight AERs at the time of entry to the study, was used to evaluate the transition rates between the three groups: normal exercise and overnight AERs, elevated exercise/ normal overnight AERs, and abnormal exercise and over- night AERs (Figure 1). Two hundred fourteen transitions were available for 138 subjects. Figure 1 shows that the

TABLE 3 Mean HbA, Values for Initial (1979-1985) and Follow-up (1988-1989) Periods

Group* No. of Subjects 1979-l 985 1988-l 989 p Value+

1 98 11.2 2 0.2* 10.9 2 0.2 0.183

z 19 9 12.4 13.1 2 f 0.3 0.7 11.6 11.9 k -+ 0.3 0.6 0.004 0.311 : 22 19 12.2 12.7 i 2 0.4 0.4 10.9 11.1 2 ” 0.3 0.3 0.0004 0.005

6 9 12.8 + 0.7 12.5 2 0.4 0.811 7 4 12.8 + 0.8 13.3 2 1.0 0.355

p Value 0.0001~ 0.0025”

* The groups are as in Table 1. The number of subjects is slightly different, as seven subjects did not have pre-1986 HbA, values. + Comparison of initial (1979-1985) and follow-up (1986-1989) values by paired Student’s t test. * Values are mean 2 SEM. * Global analysis of variance for the entire group.

EXERCISE MICROALBUMINURIA IN IOOM 157

TABLE 4 Number of Subjects with Improved or Worsened HbA, Values From Initial (1979-1985) to Follow-up (1988-1989) Values

Group’ Improved* Worsened* No Change Total

1 26 (26.5) 24 (24.5) 48 (49.0) 98 2 10 (52.6) 2 (10.6) 7 (36.8) 19 3 3 (33.3) 1 (11.1) 5 (55.6) 9 4 8 (42.1) 1 (5.3) 10 (52.6) 19 5 14 (63.6) 2 (9.1) 6 (27.3) 22 6 2 (28.6) 2 (28.6) 5 (42.8) 9 7 0 (0) 1 (25.0) 3 (75.0) 4

* The groups are as in Table 1. The number of subjects is as in Table 3. Improved or worsened is defined as a change of >lO%. The percentage distribution for each group is shown in parentheses.

transition rate between normal exercise and overnight AERs and elevated exercise/normal overnight AERs is 0.033, indicating that it would take a mean of 30 months for an individual subject to progress from normal exer- cise and overnight AERs to elevated exercise/normal overnight AERs. The transition rate for progression from elevated exercise/normal overnight AERs to abnormal ex- ercise and overnight AERs is 0.021, indicating that it would take a mean of 47.6 months to progress from ele- vated exercise/normal overnight AERs to abnormal ex- ercise and overnight AERs. The regression transition rate from elevated exercise/normal overnight AERs to normal exercise and overnight AERs is 0.138, which is 6.6 times greater than the progression from elevated exercise/nor- mal overnight AERs to abnormal exercise and overnight AERs. These data suggest the elevated exercise AER to be an “unstable” stage before development of consis- tently abnormal exercise and overnight AERs. The tran- sition rate between elevated exercise/normal overnight AERs and abnormal exercise and overnight AERs was significantly higher (p < 0.002, X2 test), however, than the direct transition rate between normal exercise and overnight AERs to abnormal exercise and overnight AERs. The median time to develop abnormal exercise and overnight AERs from normal exercise and overnight AERs was 192 months. Similarly, the median time to progress from elevated exercise/normal overnight AERs to abnormal exercise and overnight AERs was 162 months. These data show the elevated exercise AER to be a definite intermediate stage before development of consistently elevated overnight AERs. Transition rates

I #

FIG. 1 Transition rates between normal exercise and overnight albumin excretion rates (AERs), elevated exercise/normal over- night AERs, and elevated exerciseand overnight AERs. The tran- sition rate from elevated exercise/normal overnight AER was

considerably higher than from normaf exercise and overnight AERs, to abnormal exercise and overnight AERs (p < 0.0002; x2 test).

predicted elevated exercise microalbuminuria progress- ing to abnormal overnight AERs in 25% of subjects in 4.5 years, in 50% of subjects in 13.0 years, and in 75% of subjects in 28.8 years.

DISCUSSION An initially increased exercise AER was detected in 61 of 187 (33%) of this young population with Type I diabetes (groups 2, 3, 5, and 6; Table 1). If tested frequently, exercise microalbuminuria almost always is detected be- fore an increased overnight AER. Exercise microalbu- minuria is not highly sensitive as a predictor of perma- nent proteinuria, however; in the current study, 23 of the 61 subjects (39%) who initially had elevated levels had normal values on later testing. Improvement in exercise AERs was usually associated with improvement in glu- cose control (14 of the 22 subjects in group 5; Table 2).

Mean HbA, values in the 6 years before the exercise studies were started in 1986 were also likely to have an important influence on the results of this study. Thus, the two groups with significantly higher prestudy HbA, val- ues in comparison to group 1 (continued normal AERs) were group 2, which had high overnight and exercise AERs throughout, and group 4, which progressed from normal overnight and exercise AERs to elevated exercise AERs. Development of an excessive exercise AER, de- spite improvement in blood glucose control in the pa- tients in group 4, suggests that other factors besides glu- cose control are important in development of exercise albuminuria. Group 6 subjects, in whom overnight AERs progressed from normal to abnormal, had similarly high prestudy mean HbA, values, but the number in the group was too smalt to result in statistical significance. The con- fidence interval (using Tukey’s multiple-comparison test) for comparison of groups 1 and 6 was -0.14-3.62, which was close to statistical significance.

No subject with initially increased AERs on two or more exercise and two or more overnight urine samples (group 2, 11% of this young population) had normal AERs on later testing. In this group, even with improvement in mean HbA, values (p < 0.004) microalbuminuria per- sisted. Nine subjects were observed to change from in- creased exercise/normal overnight AERs to both in- creased exercise and overnight AERs (Group 6, Table 1). This type of individual is of greatest interest in predicting the course of nephropathy, as all of these nine subjects had an elevated exercise AER detected before develop-

155 GARG ETAL.

ing increased overnight AERs. Worsened or unchanged glucose control was observed in seven of the nine sub- jects.

The period of increased exercise with normal overnight AERs appears to offer a “window” during which im- proved glucose control may reverse the exercise mi- croalbuminuria and possibly delay or prevent onset of consistent overnight microalbuminuria. If glucose con- trol does not improve, the individual is more likely to progress to an increased overnight AER, with a 95% chance3 of developing diabetic nephropathy.

Andersen AR, Sandahl Christiansen J, Andersen JK, Dreiner S, Deckert T: Diabetic nephropathy in type I (insulin-depen- dent) diabetes: An epidemiological study. Diabetologia 25:496-501, 1983. Knowles HC: Magnitude of the renal failure problem in di- abetic patients. Kidney Int l(Suppl 1):2-7, 1974. Viberti GC, Jarrett RJ, Mahmud U, Hill RD, Argyropoulos A, Keen H: Microalbuminuria as a predictor of clinical nephro- pathy in insulin-dependent diabetes mellitus. Lancet 1:1430-1432, 1982.

Exercise microalbuminuria is the major factor causing variability in 24-hour or timed daytime urine collections (unpublished observations). As exercise microalbumi- nuria decreases with improved glucose control, daytime microalbumin excretion also will decrease. Therefore, we believe that overnight urine collections are more consis- tent and consequently are the preferred samples for pre- dicting diabetic nephropathy.

Parving HH, Oxenboll B, Svendsen PA, Christiansen JS, An- derson AR: Early detection of patients at risk of developing diabetic nephropathy: A longitudinal study of urinary albu- min excretion. Act Endocrine/100:550-555, 1982. Mogensen CE: Microalbuminuria predicts clinical protein- uria and early mortality in maturity-onset diabetes. N Engi J Med 310:356-360, 1984.

An increased AER after exercise is a well-recognized entity,14 even though the exact pathophysiology is un- clear. Even the 41 non diabetic controls had a higher upper limit of normal for AER after exercise (41 kg/min) as compared with overnight (7.6 kg/min); it may be partly related to the increased blood flow and pressure in the kidney as the pulsed and systolic blood pressure in- crease. Concurrent hormonal changes need further elu- cidation. The exaggerated urinary excretion of albumin during exercise may result from either increased trans- glomerular passage, decreased tubular reabsorption, or both. Future studies simultaneously measuring PP-mi- croglobulin excretion as a reflection of tubular function may determine the source of this phenomenon.

Mathiesen ER, Oxenboll 8, Johansen K, Svendsen PA, Deck- ert T: Incipient nephropathy in Type I (insulin-dependent) diabetes. Diabetologia 26:406-410, 1984. Nathan DM, Rosenbaum C, Protasowicki VD: Single-void urine samples can be used to estimate quantitative microal- buminuria. Diabefes Care 10:414-418, 1987. Sochett E, Daneman D: Screening tests to detect microal- buminuria in children with diabetes. J Pediatr 112:744-748, 1988. Brodows RG, Nichols D, Shaker G, Kubasik NP: Evaluation of a new radioimmunoassay for urinary albumin. Diabetes Care 9:189-193, 1986. Mogensen CE, Christensen CK: Predicting diabetic nephro- pathy in insulin-dependent patients. N Engl J Med 311:89- 93, 1984. Viberti GC, Jarrett RJ, McCartney M, Keen H: Increased glo- merular permeability to albumin induced by exercise in di- abetic subjects. Diabetologia 14:293-300, 1978. Mogensen CE, Vittinghus E: Urinary albumin excretion dur- ing exercise in juvenile diabetes. Stand J C/in Lab Invest 35:295-300, 1975.

Elevated exercise AERs (with a normal overnight AER) were shown, using the Markov model, to represent a defi- nite translational stage between normal overnight and exercise AERs, and abnormal exercise and overnight AERs. Most important, exercise microalbuminuria is de- tectable at a stage when reversal by improved glycemic control is still possible.

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ACKNOWLEDGMENT

This work was supported in part by Children’s Diabetes Foundation and by Grant No. RR69 from the General Clin- ical Research Program of the Division of Research Re- sources, National Institutes of Health, Bethesda, MD.

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