94

Diagnosis of Renovascular HypertensionEIGHTEEN months ago we reviewed 1 the methods

available for the diagnosis of renovascular hypertension,with special reference to the recently proposed angioten-sin infusion test.2 Although the test looked promising,we commented that methods for the diagnosis ofcorrectable renal hypertension had an unfortunate habitof turning out less satisfactory in the end than they atfirst seemed to be, and there were theoretical dangers toangiotensin infusion. Since then the value of the angio-tensin infusion test has been both denied 3-5 and con-

firmed,6-8 and the potential danger of infusing angio-tensin has been proved by the death from cerebral

haemorrhage of a healthy person during an angiotensininfusion 9 (though the duration of infusion in this casewas much longer than that required for the performanceof an angiotensin infusion test according to the schemesuggested by KAPLAN and SILAH 2). Thus, both theefficiency and safety of the angiotensin infusion test

remain in doubt, and it cannot yet be recommendedfor routine use.

As experience with the technique of the radioactiverenogram accumulates, this method seems to have moreto offer than at first appeared. Its increasing popularityperhaps reflects its safety and relative simplicity morethan its complete reliability. In principle, the methodconsists in the intravenous injection of sodium ortho-iodohippurate labelled with 1311, and the simultaneousobservation of the changes in radioactive counting-rateover the two kidneys for 15-30 minutes. Hippurate isalmost entirely cleared from the blood during onepassage through a normal kidney. After an intravenous

injection there is an initially rapid rise of radioactivityover both kidneys as the material arrives in the blood-stream. Thereafter there is a " secretory " phase duringwhich the counting-rate rises more slowly to a peak, assuccessive recirculations of blood are cleared of hip-purate. This should theoretically produce an exponentialrise of radioactivity reaching a plateau at a rate dependenton the mean circulation-time and on the proportion ofthe cardiac output passing through the kidney. After afew minutes, however, the secreted hippuran passesdown the ureters and leaves the renal area. This"

excretory " phase causes the counting-rate to declineat a rate which is the algebraic sum of the rates of uptakeand excretion of hippurate by the kidneys. The ascend-ing limb of the curve of counting-rate plotted againsttime reflects the renal blood-flow. The moment at whichthe exponential shape of the curve is lost represents thetime taken for the first labelled hippurate to pass downthe ureter, and the slope of the falling curve of radio-activity represents mainly the rate of urine flow. All thiscan be achieved with negligible radiation hazard and no

1. Lancet, 1964, ii, 1162.2. Kaplan, N. M., Silah, J. G. New Engl. J. Med. 1964, 271, 536.3. Wax, S. H. Lancet, 1965, i, 163.4. Morgan, T. ibid. p. 1222.5. Breckenridge, A. ibid. 1965, ii, 209.6. Decot, M., Guedon, J., Trad, J. J. Urol. Nephrol. 1964, 70, 723.7. D’Amico, G., Romagnoni, M. Minerva Med. 1965, 56, 4235.8. Hocken, A. G., Kark, R. M., Passovoy, M. Lancet, 1966, i, 5.9. Ames, R. P., Borkowski, A. J., Sicinski, A. M., Laragh, J. H. J. clin.

Invest. 1965, 44, 1171.

discomfort to the patient beyond that of an intravenousinjection.

Unfortunately, there are certain difficulties in themethod. If comparisons are to be made between thetwo kidneys, the counters must be well collimated andpositioned over the centre of each kidney. Many of theearly troubles with the method were due to incorrectplacing of the counters. It is generally agreed that therenogram is not suitable for the quantitative measure-ment of renal plasma-flow and urine flow-rate, becausethe actual counting-rate is critically dependent on thedepth of the kidneys from the surface, and because theinitial slope of the curve depends on whole-bodycirculation-time as well as on renal plasma-flow. Itsvalue lies in its capaciy to reveal differences between thetwo sides. Generally these differences are not in theheight of the curves, but rather in the shape of thecurves of counting-rate obtained from each kidney. Akidney with a main renal artery stenosis that is justsignificant shows a virtually normal uptake phase,presumably reflecting a normal renal blood-flow, but adelayed fall of radioactivity, suggesting a diminished rateof urine secretion or hippurate concentration on thatside. This type of abnormality can be removed in mostcases by establishing an osmotic or water diuresis, sothat urine flow is accelerated to the same rate on bothsides. A slightly greater degree of functionally effectivestenosis produces a slower than normal rise of radio-activity, corresponding to a frank reduction in renal

plasma-flow, and the rate of fall of counting-rate isfurther delayed. With a severe lesion there is definite

flattening of both uptake and excretory phases; and withvirtually absent renal function, the counting-rate rises tothe same level as the body background after injection,and thereafter remains constant.

A new review from Glasgow by LUKE and his col-

leagues 10 critically examines the efficiency of theradioactive renogram compared with other methods ofdiagnosing renovascular hypertension. In every case

they performed intravenous pyelography first, whichhad the advantage not only of locating the kidneys (sothat the counters could be positioned correctly) but alsoof identifying non-vascular lesions such as hydro-nephrosis, asymmetrical polycystic disease, and chronicpyelonephritis, which might confuse interpretation of thetracings. With the renogram performed after intra-venous pyelography, LUKE et al. discovered no false

negatives-that is, they did not miss any cases ofunilateral renal-artery stenosis in which the stenosis wasfunctionally significant in causing hypertension (asassessed either by operative relief, or by other criteria ofunilateral ischaemia such as those provided by bilateralureteric catheterisation). Similar experiences have beenreported in other series. There has been a generally lowincidence of false-positive results (1-3%)-that is, casesin which the radioactive renogram suggested unilateralrenal ischaemia but no evidence of renal-artery stenosiswas discovered. In all such cases the renogram abnorm-

10. Luke, R. G., Briggs, J. D., Kennedy, A. C., Stirling, W. B. Q. Jl Med.1966, 35, 237.

alities were of the mildest kind. A higher incidenceof false positives has been reported only when therenogram was used alone without a preliminarypyelogram.

It now seems reasonable to suggest that radioactive

renography should enter the routine clinical practice ofthose departments investigating and treating largenumbers of hypertensive patients. With careful atten-tion to detail in both tests, an intravenous pyelogramfollowed by a radioactive renogram should normally besufficient to exclude main renal-artery stenosis. Such a

screening procedure may miss the occasional case ofsegmental renal artery stenosis, perhaps occasionally amild main renal artery stenosis, and very rarely a

bilateral stenosis; but this seems to be a small price topay for the avoidance of potentially more dangerous ordifficult tests such as aortography, bilateral uretericcatheterisation studies, angiotensin infusion, and assayof pressor material in arterial or renal vein blood.Research units will doubtless continue to explore themore elaborate techniques. Of these, scanning of thekidneys after the injection of chlormerodrin labelled

with radioactive mercury 11 12 has already shown

promise. By means of this test the position and shape ofthe kidneys can be determined, and the uptake phase ineach kidney assessed without the complication of the radio-active tracer material leaving the kidney at a fast rate.

Unfortunately, once a clinician has excluded " func-tionally significant " renal artery stenosis by his favour-ite test, he then regards it as unethical to perform areconstructive remedial operation. It would be good tosee a careful trial mounted by a team uncommitted toany particular investigative technique. Every patientwould be submitted to every available diagnostic tech-nique, and all those with remediable renal arterystenosis would be operated on. We could then be

reasonably certain what screening or special proceduresshould be recommended for use in any situation. Such

aninvestigation, however, perhaps demands a more single-minded devotion to science than we can expect of

patients and most doctors. For the present we must

keep an open mind and change our techniques accordingto what common sense dictates.11. Reba, R. C., McAfee, J., Wagner, H. N. Medicine, Baltimore, 1963, 42,

269.12. Sodee, D. B. J. Urol. 1965, 84, 313.

Annotations

INDEPENDENT DISSERVICE

ON July 1 Independent Medical Services Ltd. launchedits plans for private family-doctor care in Britain. Theresult of this company’s efforts may well influence thepattern of medical care in this country for a long time tocome-and it may have its impact in other countries too.I.M.S., which has the support of the British MedicalAssociation, offers a general practitioner a contract which,it is estimated, will provide from a practice of 2000patients a gross income of El 4,000 a year: the cost of thedrugs his patients need will be deducted (an estimatedE5400) and practice expenses are put at E2600, leaving anet taxable income of 1;6000-from 2000 patients. Patientswill pay a basic subscription of E7 10s. a year, save thoseup to the age of 17 and those over 65, who will pay onlyE4 10s. Additional mileage payments will be charged topatients living more than 2 miles (12s. a year) or more than5 miles (El 4s.) from the doctor’s surgery. For each

surgery consultation a patient will pay 2s. 6d., for eachdomiciliary visit between 8 A.M. and 8 P.M. on a weekday5s., and for other visits 1Os. I.M.S. also offers a

"

drugs forprivate patients " scheme which (for E4 a year) will coverthe cost of drugs prescribed for a patient who chooses topay his doctor by the old private method. The dispensingside of all these arrangements has been organised in

cooperation with the Pharmaceutical Society. To providethe capital to establish I.M.S., doctors were asked to giveE10 each, and the expectation was that a minimum ofE80,000 would be needed. In the event, about 6000 doctorshave supplied money, but the company decided to goahead on E60,000 and offer the new service to these 6000and their patients. Last week the number of generalpractitioners who had actually signed a contract withI.M.S. Ltd. stood at about 300.The objection to the independent service is that no

general practitioner who encourages his N.H.S. patients

to subscribe to I.M.S. can legitimately offer those whodo so anything more than time taken from those who donot. For that reason alone, we cannot support the doctorswho now embark with I.M.S. in an organised attemptto extend private practice at a time when the countrylacks doctors, and who yet retain substantial N.H.S.lists. As an increasing number of N.H.S. practitionersadopt appointment systems, this solitary attraction ofI.M.S., with its heavy hint of buying the doctor’s time atothers’ expense, may abate. Surveys of public opinion,quoted in support of I.M.S., have indicated that 30%(maybe more) of people in Britain would prefer to makeprivate provision for their medical care. But the numberwho have responded to the general-practitioner schemeoffered by the British United Provident Association

(though admittedly the offer is restricted to the 11/4 millionsubscribers and dependants who already pay B.U.P.A. tohelp them with private hospital treatment) suggests that30% is not the true figure: in fact, only 22,000 people arecovered by the original B.U.P.A. scheme for generalpractice, which has operated since 1959. (This scheme isnow to be extended, also from July 1, to offset the cost ofprescribed drugs and in other ways.)Though the independent service is presented by its

advocates as a manifestation of traditional British freedom,as a pacemaker to the National Health Service, and evenas its saviour (by discouraging the emigration of doctors),it is plainly recognisable as the work of that powerfulfaction in the B.M.A. whose bitter dislike of the N.H.S.has always prevented them from giving their full supportto what is incontrovertibly best for the patient-namely,a service which cares for him strictly according to hismedical needs and takes no account of how he pays for it.It hardly needs saying that every doctor has the right topractise under whatever arrangements he chooses; and heis utterly free to withdraw as an individual from the N.H.S.But just as organised withdrawal, being a threat behind apay claim, was wrong, so is the B.M.A.’s latest action tobe deplored, for the Association is supporting a concerted