55

CIinica Chimica Acta, 71 (1976) 55-59 0 Elsevier Scientific Publishing Company,

Amsterdam

- Printed in The Netherlands

CCA 7927

URINARY DIABETIC

ALBUMIN EXCRETION SUBJECTS

R.J. JARRETT

*, N.P. VERMA ** and H. KEEN

Unit for Metabolic Medicine, Department London, SE 1 9RT (U.K.) (Received

IN NORMAL AND

of Medicine, Guy’s Hospital, London Bridge,

March lOth, 1976)

Summary Using an albumin radio-immunoassay, urinary albumin concentration and excretion rate have been measured in diabetics and control subjects .ovemight, after several hours ordinary activity and during two successive one hour periods of recumbency. The urine albumin concentration was relatively constant throughout each of the four collection periods. Variations in albumin excretion rate were directly related to changes in urine flow. In assessing changes in urinary albumin, concentration and urine flow should be reported as well as the calculated albumin excretion rate. In the diabetics, selected for absence of clinical proteinuria, the mean concentration of albumin did notdiffer significantly from that of the controls. The overnight albumin excretion rate was higher in the diabetics, but this was due to the greater volume of urine.

Introduction Urine albumin excretion rates have been shown to be increased in newly diagnosed, untreated maturity onset diabetics and ‘borderline’ diabetics [ 11, similarly in newly diagnosed juvenile diabetics [ 21 and in patients with inadequately treated hypertension [ 31. This increase is at a level well below that recognised by routine clinical testing. In the juvenile onset diabetics treatment with insulin led to a fall in albumin excretion [2]. In treated diabetics, with urines negative to Albustix, increased albumin excretion has been observed by Balodimos et al. [4] but not by Mogensen [2]. The quantity of albumin and other proteins in the urine must depend upon the balance between glomerular filtra* To whom correspondence should he addressed. ** Present address: Department of Medicine, Maulana Azad Medical College, New Delhi - 1, India.

56

tion and tubular reabsorption and, possibly, of secretion. The factors responsible for variation in albumin excretion are ill-understood. We have, therefore, investigated the effects of posture and of rate of urine flow upon albumin excretion in diabetics and in non-diabetic controls in the hope that this might cast some light on the processes involved, and provide further information on the earliest changes in renal function in the diabetic. Procedures Subjects were instructed to empty their bladders immediately before going to bed, noting the time. A container was provided for the first urine passed next morning (or during the night); the time of this voiding was again noted. Controls and diabetics, if out-patients, brought the complete overnight urine (Ul) to the hospital by 09.00 h, when the bladder was again emptied, the urine collected and its volume measured (U2). The diabetics had their normal treatment and diet. From 09.00 to 11.00 h subjects lay supine, providing further complete urine samples at 10.00 (U3) and 11.00 h (U4). The volume of each urine sample was measured and an aliquot frozen for subsequent measurement of albumin concentration by a radio-immuno-assay method [ 51. The diabetics studied included 5 insulin-dependent and 6 maturity-onset patients and were selected to include a range of known duration of diabetes from l-10 years. Patients with proteinuria detectable by Albustix were excluded. Fluid intake at home was not controlled, but subjects were asked not to drink after 09.00 h. Results The mean concentration of urinary albumin and the calculated mean albumin excretion rates in the different collection periods are presented in Table I for both patients and controls. The albumin concentration in overnight urine was slightly lower in the diabetics. Both in diabetics and controls the changes in

TABLE MEAN

I (i

S.E.M.)

COLLECTION Collection min

periods:

periods

Collection

Controls

ALBUMIN

CONCENTRATION

AND

ALBUMIN

EXCRETION

IN THE

FOUR

1.

overnight;

2.

from

rising

to beginning

of recumbent

periods:

3 and

excretion

rate

4, successive

or recumbency.

period:

Albumin

concentration

Albumin

(mg/lOO

ml)

Wg/min)

1

2

3

4

1

2

3

15.18

4

(n = 11)

Meall

0.558

0.628

0.682

0.533

4.30

4.19

S.E.M.

0.058

0.146

0.134

0.071

0.47

1.04

Diabetics

RATE

PERIODS

2.81

12.5 2.63

(n = 12)

Mean

0.502

0.452

0.511

0.438

6.09

9.10

9.09

S.E.M.

0.037

0.044

0.062

0.039

0.72

1.54

2.27

10.09 1.71

60-

57

TABLE II RESULTS

FOR

FOR CONTROLS

EACH

COLLECTION

AND DIABETICS

PERIOD

WERE

COMPARED

USING

THE PAIRED

‘t’

TEST

SEPARATELY

The table shows the statistically significant @ < 0.05) differences.

‘t’

Comparison

value

Controls Albumin concentration. periods 3 and 4 Albumin excretion rate Periods 1 and 3 Periods 1 and 4 Periods 2 and 3 Periods 2 and 4 Periods 3 and 4

2.11 3.52 3.27 3.89 3.10 2.02

Diabetics Albumin concentration periods 1 and 4 Albumin excretion rate Periods 1 and 2 Periods 2 and 3 Periods 2 and 4

1.87 2.43 2.75 3.46

concentration in the four collection periods were small, although some of the differences were statistically significant (p < 0.05; Table II). In the control group there was a small rise in mean concentration in the urine collected during the period when the subjects were up and about (period 2) compared with the overnight and second recumbent periods, but neither difference even approached statistical significance (Table II). Only one control, and no diabetic, had a substantially increased urine albumin concentration during collection period 2, his results being 0.7, 1.88, 1.53 and 0.93 mg/lOO ml, respectively, for the four periods. Much greater variation was observed in urine volumes and hence in the calculated albumin excretion rates. The mean overnight excretion rate was significantly greater in the diabetics than in the controls, but the effect of recumbency appeared much less pronounced. This was associated with higher urine flows (Table III) as were the greater albumin excretion rates during subsequent collection periods in both groups of subjects. Albumin excretion rates thus clearly correlate with urine flow and the nature of the relationship was exam-

TABLE III MEAN (k S.E.M.) URINE FLOW DURING THE FOUR COLLECTION

PERIODS

Urine flow (ml/min) Collection period:

1

2

3

4

Controls

0.96 + 0.09

Diabetics

1.39 ? 0.18

0.91 + 0.27 0.77 + 0.14

3.48 + 0.77 2.06 + 0.27

3.42 _+0.89 3.34 f 0.53

58

3.5

2

2.5

5 2 0

2.0

i ._s f ;

1.5

d

1.0

0.5

0

1

r

0

1

1

;

j

4’ Urine

; Flow

d

7

;r

b

lb

Rate (ml/min)

Fig. 1. Correlation between excretion rate and urine flow rate for each collection period in patients and controls. The regression lines were calculated using a least squares method. The correlation coefficients were 0.885 (controls) and 0.782 (diabetics).

ined in diabetics and controls. The best fit for the data is curvilinear, where the function is cubic or quadratic in form, though the data can be almost as readily fitted to a linear function (Fig. 1). Discussion Most previous reports on micro-albuminuria in diabetics and others have paid little attention to urine flow rates in the evaluation of albumin excretion. Mogensen [2] states that albumin excretion rates were ‘not correlated with diuresis’ in his diabetic patients, but does not present the data nor define ‘diuresis’. Our present results indicate that albumin concentration in the urine is held within a fairly narrow range, at least under the special conditions of this study. The considerable variation in calculated albumin excretion rates is directly related to urine flow rates, suggesting that the mechanisms responsible for tubular reabsorption of albumin tend to control the final concentration. This may ultimately depend mainly upon the concentration of albumin in the glomerular filtrate, which itself is determined by the glomerular filtration rate and the permeability of the glomerular capillary membrane. If albumin is removed in equal quantities with water by reabsorption down the tubules, the final concentration in the urine would be approximately equal to that in the glomerular filtrate and the amount secreted would then be determined, at least at a low level of excretion, by the urine flow rate.

59

In our subjects, there was no significant change in urine albumin concentration during the period of activity and predominantly upright posture compared with the overnight urine. In the normal subjects there was also no change in albumin excretion rate; in the diabetics there was a significant increase, but this was related to an increased urine flow. It would be desirable, in order to complete the comparison, to provoke an equal increase in urine flow in control subjects and note the effect on albumin concentration. Mogensen [2] reported a higher albumin excretion rate during the day (9.7 (ug/min) than during the night (5.1 I.cg/min), but this might be explicable by the greater diurnal urine output. Our results are consonant with those of Mogensen [2] in that the albumin concentration and excretion rate were not significantly greater in the diabetics selected for absence of ‘clinical’ proteinuria, even though half of them had known diabetes of duration exceeding five years. Mogensen’s view that the glomerular basement membrane thickening which can be demonstrated after 3-4 years of diabetes [6] does not have a necessary influence upon albumin excretion may thus be true when the amount of albumin presented to the tubules is within their reabsorptive capacity. Nevertheless, it may be possible to provoke increased albuminuria by a variety of methods, and Mogensen and Vittinghus [7] have recently shown that a given level of exercise will increase the albumin excretion rate in diabetics, but not in controls. This increase is unlikely to be related to changes in GFR, for although changes in total protein excretion have been shown to be directly related to changes in GFR [8] the GFR falls with exercise [9]. Changes in tubular reabsorption are more likely to be responsible, for exercise has been shown to diminish tubular reabsorption of certain urinary proteins [9]. The increased albumin excretion rate which we demonstrated in newly found diabetics and borderline diabetics [l] was not due to greater urine volumes; similar differences were also observed in albumin concentrations in urine. The apparent discrepancy between these and the present observations may be due to a long period of unrecognized hyperglycaemia in the middle-aged and elderly subjects detected in the Bedford Survey, a view supported by the observation that 7% of the newly found diabetics had evidence of diabetic retinopathy at the time of detection. Acknowledgments We thank Mrs. S. Pinney and Miss K. Stringer for performing the assays, and Dr. D.A. Pyke and Dr. P.J. Watkins for allowing us to study patients under

their care. Dr. N. Veal1 kindly provided

the labelled albumin.

References

5 6 7 8 9 10

Keen, H.. Chlouverakis. C., Fuller, J. and Jarrett. R.J. (1969) Guy’s Hosp. Rep. 118. 247-254 Mogensen. C.E. (1971) Stand. J. Clin. Lab. Invest. 28, 183-193 Pawing. H.-H., Jensen. H. AE., Mogenson. C.E. and Evrin,P.-E. (1974) Laneet i, 1190-1192 Balodimos. M.C.. Chlouverakis. C.. Gleason, R.E.. Jarrett. R.J., Kahn, C.B.. Keen, H. and Soeldner, J.S. (1971) Lancet ii, 239-242 Keen, H. and Chlouverakis. C. (1963) Lancet ii, 913-914 &&by, R. (1975) Acta Med. Stand. 191. Suppl. 574 Mogensen, C.E. and Vittinghus, E. (1975) Stand. J. Clin. Lab. Invest. 35, 295-300 Sharma, B.K., Gandhi, V.. Pillay. V.K.G., Smith. E.C. and Dunea, G. (1971) Lancet i. 369-371 Wesson. L.G. (1969) in Physiology of the human Kidney, pp. 96-108, Grune and Stratton. New York Poortmans. J.R. (1972) Clin. Sci. 43. 115-120