Community nephrology: audit of screening for renal insufficiency in a high risk population

Lu Kissmeyer, Chiew Kong, John Cohen1, Robert J. Unwin, Robin G. Woolfson and Guy H. Neild

Institute of Urology and Nephrology, University College London Medical School and 1 Primary Health Care and Population Sciences, UCL, London, UK

Correspondence and offprint requests to: Professor G. H. Neild, Department of Nephrology, Middlesex Hospital, Mortimer Street, London W1N 8AA, UK. email: g.neild{at}ucl.ac.uk



   Abstract
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Background. The rate of acceptance onto dialysis programmes has doubled in the past 10 years and is steadily increasing. Early detection and treatment of renal failure slows the rate of progression. Is it feasible to screen for patients who are at increased risk of developing renal failure? We have audited primary care records of patients aged 50–75 years who have either hypertension or diabetes, and are therefore considered to be at high risk of developing renal insufficiency. Our aim was to see whether patients had had their blood pressure measured and urine tested for protein within 12 months, and plasma creatinine measured within 24 months.

Methods. This was a retrospective study of case notes and computer records in 12 general practices from inner and greater London. A total of 16 855 patients were aged 50–75 years. From this age group, 2693 (15.5%) patients were identified as being either hypertensive or diabetic, or both.

Results. Of the 2561 records audited, 1359 (53.1%) contained a plasma creatinine measured within 24 months, and 11% of these (150) had a value >125 µmol/l. This equates to a prevalence of renal insufficiency of >110 000 patients per million in this group. Forty two patients (28%) had been referred to a nephrologist. Of records audited, 73% contained a blood pressure measurement and 29% contained a test for proteinuria within 12 months.

Conclusions. There is a high prevalence of chronic renal insufficiency in hypertensive and diabetic patients. It is feasible to detect renal insufficiency at a primary care level, but an effective system will require computerized databases that code for age, ethnicity, measurement of blood pressure and renal function, as well as diagnoses.

Keywords: community; diabetes; hypertension; primary care; proteinuria, renal insufficiency; screening



   Introduction
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Renal dialysis centres in the UK are overwhelmed by the increasing numbers of patients accepted for renal replacement therapy (RRT) [1]. UK acceptance rates for RRT had increased from 20 per million population (pmp) in 1982 to 82 pmp in 1995 [2] and continue to rise in a linear manner [3]. The national acceptance rate of 82 pmp is an underestimate for London, and many major cities, where there are large populations of ethnic minorities in whom renal failure is known to be 3–6 times more common [4,5]. This is supported by variation in acceptance rates in the Thames Region (London) for 1991–1992 that were 61 pmp for white people, 175 pmp for black people and 178 pmp for Asian people [6].

The incidence of end-stage renal failure (ESRF) rises exponentially in the last decades of life from ~80 pmp at the age of 50 years to 800 pmp in 80 year olds [7,8], and much of this increased incidence is attributed to diabetes and hypertension. The age threshold of elderly patients considered suitable for dialysis has also risen continuously. In the US, 21% of those on the RRT programme are aged 65–74 and 11% are 75 years or older [7]. As yet, in our own renal unit, only 15% of our patients are 65–74 years of age and 4% >75 years, but further expansion of the numbers of elderly patients treated in the UK is likely.

Of those taken onto dialysis, 30–50% still present de novo, require dialysis within days or weeks [9] and have a greater mortality [10]. In many of these patients, early treatment can delay or prevent deterioration in renal function [1113], but this depends on earlier detection which must be achieved at the primary care level. We therefore investigated whether it is feasible to screen for patients in primary care who, as a result of their primary diagnosis, age or ethnic origin, are at increased risk of developing renal failure. Patients considered to be at high risk are those aged 50–75 years either from ethnic minorities or known to have either diabetes or hypertension, or a family history of either. In 12 general practices, we have audited case records from this group to see whether they are having their blood pressure and renal function (plasma creatinine) measured, and their urine tested for proteinuria.



   Patients and methods
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Nine inner city and three peripheral general practices from the north east Thames region of London were recruited to give us an estimated base population of ~80 000 patients.

Patients
Patients considered to be at risk of renal insufficiency were those aged 50–75 years either from ethnic minorities, or known to have either diabetes or hypertension or a family history of either. Patients' records were audited for: (i) blood pressure; (ii) proteinuria; and (iii) plasma creatinine.

Definitions
Diabetes.
Patients were considered to have diabetes, either if they were coded as having diabetes, or if they were on anti-diabetic medication.

Hypertension.
All practices followed British Hypertension Society management guidelines [14]. Patients were considered to have hypertension, either if they were coded as having hypertension, or if they were on blood pressure lowering therapy, or if they had two or more recordings >160/90 mmHg. All diabetics were excluded from this group.

Proteinuria.
Persistent proteinuria of a trace or more on Dipstix was considered as significant, but it was recommended that this was confirmed by sending a spot urine sample to the laboratory for estimation of the protein/creatinine ratio (normal range 0–12 mg protein/mmol creatinine).

Renal insufficiency.
This was defined as a plasma creatinine concentration >125 µmol/l.

Plan of investigation
Audit.
The 12 practices had a base population of 71 091 patients of whom 23.7% (range 16–31%) were aged 50–75 years. Case notes were audited of those aged 50–75 years identified as having hypertension or diabetes. Notes were reviewed to see whether, in the past 12 months, patients had had their blood pressure measured, their urine tested for protein, or in the past 24 months their plasma urea and creatinine concentration measured.



   Results
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 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Audit of hypertensive patients (Figure 1Go)
A total of 1880 patients aged 50–75 years were recorded as having hypertension, which represented 11.2% (range 5.8–14%) of that age group.



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Fig. 1. Hypertensive audit.

 
Measurement of blood pressure in the past 12 months was audited in 973 patients in seven practices. Of these 714, 73.4% (range 33–94%), had had their blood pressure checked, of whom 245, or 34.3% (range 30–64%), had a blood pressure >160/90 mmHg (see Figure 1Go).

Proteinuria was audited in 901 of these 1880 hypertensive patients in six practices. Of these, 202, or 22.4% (range 7–36%), had had their urine tested in the past 12 months. Thirty one of these 202 patients, or 15.3% (range 10–75%), had proteinuria and, of these 31 patients, 25 (81%) had also had their plasma creatinine measured within 24 months.

Creatinine was audited in 1800 patients in 11 practices. A total of 958 patients, or 53.2% (range 20–70%), had had their plasma creatinine checked in the previous 2 years, and 102, or 10.6% (range 3–26%), were found to have a plasma concentration >125 µmol/l. This is equivalent to a prevalence of renal insufficiency of 106 000 pmp in this hypertensive population. Only 27 of these 102 patients (26%) had been referred to a nephrologist.

Audit of diabetic patients (Figure 2Go)
A total of 813 patients aged 50–75 years were recorded as having diabetes, which represented 4.8% (range 2.9–10.7%) of that group.



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Fig. 2. Diabetic audit.

 
Measurement of blood pressure in the past 12 months was audited in 304 patients in six practices. Of these, 223, or 73.3% (range 46–86%), had had their blood pressure checked, and 57, or 25.6% (range 0–41%), had a blood pressure >160/90 mmHg.

Proteinuria was audited in 240 of these 772 diabetic patients in five practices. Of these, 127, or 52.9% (range 10–77%), had had their urine tested in the past 12 months. Seventeen of the 127 (13.4%) had proteinuria and 15 out of the 17 (88%) had also had their creatinine measured.

Creatinine was audited in 761 patients in 11 practices. Of these, 401, or 53% (range 37–89%), had had their plasma creatinine checked in the previous 2 years, and 48, or 12% (range 9–25%), were found to have a plasma concentration >125 µmol/l. This is equivalent to a prevalence of renal insufficiency of 120 000 pmp in this diabetic population. Eleven of these 48 patients (23%) had been referred to a nephrologist.

Combined audit of all hypertensive and diabetic patients at risk of developing ESRF
A total of 2693 patients aged 50–75 years were recorded as having hypertension and or diabetes. In total, 1277 records were audited for blood pressure and 937 of them (73%) had had a blood pressure recorded in the past 12 months. Proteinuria was audited in 1140 records and, in 329 (29%) of them, the urine had been tested in the past 12 months. Creatinine was audited in 2561 patients; 1359 of them (53%) had had their plasma creatinine checked in the previous 2 years and 150, or 11%, were found to have a plasma concentration >125 µmol/l. This is equivalent to a prevalence of renal insufficiency of 110 000 pmp in this population. Only 38 of these 150 patients (25%) had already been referred to a nephrologist.



   Discussion
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
This audit of 12 general practices in north east London confirms the high prevalence of chronic renal insufficiency in patients with diabetes and hypertension. The overall prevalence of renal insufficiency in this selected population was 110 000 patients pmp, and only 25% of those patients identified had been referred for nephrological assessment. Referral of all appropriate patients would overwhelm available renal services. This large population could be managed in the community, but clinical care pathways need to be developed to screen, investigate and manage these patients at risk. Realistically, such protocols could be supervised by practice and community nurses.

Hypertension
Since 1990, it has been recommended that blood pressure should be measured and urine tested for albumin and glucose by general practitioners at 3 yearly intervals in patients aged 16–74 years [15]. British Hypertension Society guidelines recommend that blood pressure is kept below 160/90 mmHg [16], and all hypertensive patients should undergo urine analysis (Dipstix) and measurement of serum electrolytes, urea and creatinine [16,17] In addition, those patients suspected of having hypertension secondary to renal disease should be referred for specialist advice [16]. Once controlled, blood pressure should be measured at 3 monthly intervals, although it is recognized that currently only half the patients achieve a target blood pressure of <160/90 mmHg [16,18]. Our audit showed that blood pressure had been measured within the last 12 months in 73% of hypertensive patients but, encouragingly, the pressure was >160/90 mmHg in only 34% of them. This may reflect the lower pressures that are measured in the community compared with hospital clinics [19]. The percentage of our hypertensive population who had had a follow-up blood pressure measurement was similar to that reported in a 3 year follow-up study of three general practices in Oxford [20] and one in Ireland [21]. Urine had been tested for protein in only 22.4%, and plasma creatinine measured within 24 months in 53.2% of the hypertensive patients. We have not found comparable published data. A frequent reason for measuring creatinine was starting an angiotensin-converting enzyme (ACE) inhibitor.

Diabetes
The British Diabetic Association `Report on renal disease in diabetes' recommends that all diabetics should have their urine tested for albumin excretion and blood pressure measured at least once a year [22]. Blood pressure should be kept below 140/90 mmHg. Patients with proteinuria should be monitored on average three times a year, and renal function should be checked `regularly' [22]. Blood pressure had been measured within the last 12 months in 73% of our diabetic patients, and the blood pressure was >160/90 mmHg in only 26% of diabetic patients. Urine had been tested for protein in 53% and plasma creatinine measured also in 53% of the diabetic patients.

The practices that have taken part are a typical cross-section of practices in the north Thames region. Only one practice did not have a computer, but even the two practices most comprehensively computerized felt that the individual records had to be reviewed if data were not to be missed. All computerized practices had recorded the identity details and diagnoses of patients; however, no practice kept data on the ethnic origin of their patients. Details of family history were not recorded on the computer in any reliable manner, and no practice had computerized records of urine testing, blood tests or blood pressure measurement for more than 12 months. In individual practices, standardized protocols for entering data into the computer often did not exist, with different doctors recording different data. Audit of blood tests (plasma creatinine) was generally the easiest and most reliable as samples were all sent to hospital pathology departments. Since >90% of the practice population aged between 50 and 75 years will be seen in a 3 year period, it is imperative that protocols are in place for the routine screening at these random visits. Ideally, results would be recorded on the practice computer, and patients who had not been screened within a given period would be invited to come. Surveillance of patients from ethnic minority groups and those with a family history of hypertension or diabetes should be even more rigorous. Epidemiological studies suggest that only half of the hypertensive population is recognized.

Plasma creatinine concentration is an excellent index of renal function but is related to muscle mass. Although most laboratories in north London quote an upper normal limit of 125 µmol/l, this would only be achieved in a few healthy young muscular males. In the population we have studied, values of urea or creatinine consistently above the upper limit of normal would indicate a glomerular filtration rate of <50 ml/min/1.73m2. Of those hypertensive patients who had had their plasma creatinine measured, 11% had a concentration >125 µmol/l, and the corresponding figure for diabetic patients was 12%. Early detection of renal insufficiency is vital as careful control of hypertension is known to slow or prevent the progression of many forms of renal failure. This has been clearly established for insulin-dependent diabetic patients (IDDM) [23,24], and for NIDDM and in non-diabetic renal failure [13,25,26]. ACE inhibitors seem to be particularly effective in preserving renal function if there is significant proteinuria [12,13], but careful control of hypertension by whatever drug regimens is the overriding aim.

In summary, established guidelines already indicate that any patient with hypertension or diabetes should have their urine tested for proteinuria and positive tests quantitated, and their renal function determined by measurement of plasma creatinine and urea. Whenever possible, such patients should be investigated appropriately, good control of their blood pressure achieved and advice given regarding diet and life style. An effective system of surveillance and treatment will require computerized databases that code for age, ethnicity, family history, measurement of blood pressure and renal function.


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Table 1. Demographic details of general practices audited
 


   Acknowledgments
 
We are very grateful to all those general practitioners and their staff who took part in the study, and to Zenecca pharmaceuticals for their support without which this study would not have been possible. We would also like to thank Drs H. S. Cairns, F. D. Thompson and P. J. Roderick for their advice and comments, and Merck, Sharpe and Dohme for their support for C.K.



   Notes
 
Editor's note

Please see also Editorial Comment by Jungers (pp. 2082–2084) in this issue.



   References
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 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 

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Received for publication: 15. 9.98
Accepted in revised form: 8. 1.99