The important part which the laboratory has come to play in medical
science is generally accepted and appreciated, but the relation which
it should bear to clinical practice remains to be satisfactorily
defined. It is obvious to all clinicians of experience that the
laboratory never can become, and never should become, the predominating
factor in the practice of medicine, but it is equally evident that
sound medicine cannot be carried on without the support of the
laboratory, and that in the future the dependence of the clinic on the
laboratory will probably increase rather than decrease. Among the men
engaged in active medical practice, however, only a small minority
can ever hope to undertake extensive laboratory work in connection
with their patients, and the great majority of physicians are and will
continue to be confronted by the difficult problem of their relation
to this growing influence in medicine. To the teacher of medicine,
whose foremost duty is to prepare his students for the practice of
the future, the same problem presents itself, for the students must be
thoroughly trained in the laboratory methods that will be of practical
service, but not burdened with those that are highly specialized or of
questionable value.
The leading exponents of clinical laboratory work are the large
hospitals--especially the hospitals associated with teaching
institutions--and these exert a profound effect on private medical
practice, but the conditions existing in them are such as to demand a
separate consideration. In such hospitals, laboratory investigations
fall into one of three categories. The first includes those which
belong to the field of pure research, their object being to advance
the limits of our knowledge of disease. With this we have, at present,
no concern. The second consists of those laboratory methods that are
applied in order to obtain direct aid in the diagnosis or treatment
of individual cases of disease. This often means the use of standard
methods of proved and known value--methods which have received general
professional acceptance--but in addition it means the use of many
methods of possible value, the significance of which needs to be
thoroughly tested under conditions favorable for critical control. The
trying out of newly advocated measures for the diagnosis and treatment
of disease must always be an important function of the larger and
better equipped hospitals. Many--indeed the majority--of such methods
are found to be unreliable or of little practical value, and after
their status becomes established they are discarded. Very rarely a new
method withstands the test of prolonged observation and proves to be
of such practical significance that it can be properly advocated for
general adoption. This type of hospital thus serves as the court before
which all such new ideas must stand trial and it is astonishing, if
not depressing, to compare the enormous amount of time and labor that
is spent in gathering evidence with the comparatively meager results
that pass the tests. The burden added to the hospital laboratories by
such work is very great, but the importance of the function cannot
be overestimated, for it filters out what is useful and protects the
profession from much that is worthless.
The third category under which hospital laboratory work is carried
on depends on the fact that every hospital is, or should be, an
educational institution, and one of its primary duties is the
instruction of all the members of the staff in the nature of disease.
Many of the laboratory data, therefore, that fill the pages of
carefully compiled hospital records do not have a direct diagnostic
or therapeutic bearing on the individual case, but they contribute
information which throws light on the pathological physiology and
clarifies the disease process. In so far as the accumulation of such
accessory laboratory observations is instructive to those who are
studying the patients, the work is more than justified, but if, as
sometimes happens, particularly with the younger members of the staff,
it leads to the idea that all these observations are necessary for
the proper diagnosis and treatment of any given case, the result may
be most unfortunate. Properly used, such laboratory observations are
enlightening and broadening; improperly used, they are blinding and
narrowing. The real reason for taking an electrocardiogram on every
patient with a cardiac arrhythmia is so that after one has studied the
records of a large series of cases, he may understand the clinical
manifestations of cardiac irregularities so well that he is able
to recognize the type of arrhythmia without the electrocardiogram.
His increased knowledge should, on the one hand, emancipate him
from the need of the complicated apparatus in most cases, and, on
the other hand, help him to appreciate the occasional case in which
careful instrumental study is desirable. From this point of view,
therefore, much hospital laboratory work may be regarded as of indirect
significance for the individual patient, but aimed at the training
of better clinicians. When, as sometimes happens, it results in the
production of poor clinicians, unable to interpret disease except
through the eyes of the laboratory, its purpose has failed, and failed
seriously.
The physician engaged in the actual practice of medicine is directly
concerned, therefore, with only a small part of the laboratory work
which is carried on in the larger hospitals, for his attention must
necessarily be focussed entirely on those methods which contribute
immediately to the better care of his patients. The methods of the
teaching clinic cannot and should not be carried into extramural
practice. In the hospital all manner of tests can readily be performed
in obscure or doubtful cases, but in private practice the economic
factor usually restricts one to the tests which most obviously offer
practical assistance. Fortunately, however--and this is apparently
contrary to much present-day opinion--good medicine does not consist
in the indiscriminate application of laboratory examinations to
a patient, but rather in having so clear a comprehension of the
probabilities and possibilities of a case as to know what tests may
be expected to give information of value. Even so-called thoroughness
should be tempered by reason, and the reason that must dictate the part
which laboratory tests shall play in any given case must be the result
of a combination of clinical experience with an understanding of the
physiological significance of the available tests.
For the physician in private practice laboratory tests fall into two
main classes. The first consists of those which every educated doctor
should be able to carry out, and the second consists of tests which are
more difficult in technique and which should be attempted only by a
limited number of men who have been able to devote the time necessary
to acquire specialized training. Fortunately, the first class is by far
the more important of the two.
The laboratory tests which should be at the command of every
practitioner of medicine are those which deal with the more important
and practically useful examinations of the blood, urine, feces, gastric
contents, spinal fluids, pleural and ascitic fluids. These are the
tests that are customarily taught in the medical schools in the course
in clinical pathology, and the instruction is usually designed to
take up the laboratory methods that are absolutely necessary for good
practice and those only. An experience in teaching this subject during
the last seven years has emphasized the striking fact that in spite
of the great contributions which the laboratory has made to clinical
medicine there has been surprisingly little change in the character or
number of the technical methods which are essential for good practice.
In many instances the progress of medical science has resulted in a
clearer, broader, and more helpful interpretation of the tests, but
the actual technical procedures have not been greatly altered and they
are still available to the trained man who has a minimum of laboratory
apparatus. It has, indeed, been interesting to find how little new
material in the way of technical procedure could justifiably be added
to the course from year to year, even though the literature and the
practices of various clinics were carefully followed in the attempt
to keep the course up to date. The methods for the examination of the
urine, for instance, are taught much as they were two decades and more
ago. Certain tests, such as urea determinations, have been discarded
and others are regarded as having a different significance, but the
records still show the color, specific gravity, reaction, albumin and
sugar content, and the microscopic examination of the sediment. These
simple observations, correctly used and interpreted, are practically
all that is necessary in cases of nephritis. The modern “two hour renal
test” requires nothing more than determinations of volume and specific
gravity, and if it is combined with the phenolsulphonephthalein
test--the technique of which is entirely simple--the field is open for
the study of renal function. It is far more important to understand
the significance of these easy tests than it is to worry about the
quantitation of blood urea or blood uric acid. The situation is much
the same with regard to hematology. The technical procedures of primary
value are now as they have been for years, the counting of white cells
and red cells, the estimating of hemoglobin, and the preparation of
stained specimens of blood. Quite recently the students at the Harvard
Medical School have also been instructed in the methods of counting
platelets and of staining reticulated cells, but neither of these
procedures involves any essentially new technique. With these, and one
or two other tests, such as coagulation time and bleeding time, the
field of hematology is open. Again, the technique has been altered but
little, and little has been added to it, but modern investigations
have brought to it a greater significance. In the examination of the
spinal fluid the cell count, which is the most important point, is
merely an adaptation of the method of counting blood leucocytes, and
not a new technical process. With regard to the examination of the
gastric contents, body fluids, and feces, the same argument holds
true; none of them involves difficult or prolonged examinations or
expensive apparatus, and all of them yield information of the highest
value to the man trained in their use and interpretation. Here,
however, is the crux of the situation. All of these so-called routine
tests are easy and consume little time in the hands of a trained man,
but they are difficult, time-consuming, and of little value in the
hands of an untrained man. What is really needed in the application
of laboratory methods to the practice of medicine is not a knowledge
of more technical procedures, but a much more exact knowledge of a
few. Experience has shown that a proper degree of technical skill can
rarely be obtained during the medical school course, and it should be
the duty of every hospital to see that no house officer receives his
diploma unless he has demonstrated an ability to perform satisfactorily
all the simpler laboratory examinations and has shown a knowledge of
how to use the results in the study of his patient. If every physician
was so much at home with the technique of the simpler tests that it was
quicker for him to apply them than to wonder whether they were worth
while applying, and if he understood how to interpret these tests and
gain the maximum information from them, the problem of the relation of
the physician to the laboratory would be largely settled.
The second group of laboratory methods having a direct bearing on
the practice of medicine consists of those which involve highly
specialized technique and complicated apparatus. Electrocardiography,
basal metabolism determinations, the Wassermann reaction, clinical
bacteriology, and the various types of chemical analysis of the blood
fall into this category. The information to be elicited from these
and other analogous methods is often extremely valuable, but their
application is necessary only in a comparatively limited number
of cases. As a whole, these methods do not have the broad general
significance and importance that characterize the simpler tests just
referred to. It is, of course, highly desirable that they should
be available to practicing physicians, so that they may be used in
the cases in which they are particularly indicated, but fortunately
there is no necessity for the great majority of physicians to bother
themselves about the details of technique. This should be relegated to
a small number of men who are devoting their attention to specialized
fields. Simplified technical procedures, supposed to be adapted to
the use of practicing physicians, are continually being advocated as
substitutes for the recognized standard methods employed in performing
some of these tests, but they are frequently unreliable, or reliable
only in the hands of one who has a thorough knowledge of all the
sources of error, so that it is far wiser to avoid them and to obtain
the dependable observations of experts. The clinician may, therefore,
neglect the technical side of these more elaborate tests with a clear
conscience, but in so doing he should not feel that he may drop the
matter entirely. If he is ever to make use of them--and this the
welfare of his patients may demand--he must have an understanding
of their significance and of the physiology underlying them. He
must know when they are indicated and when they cannot be expected
to give important evidence. A little insight into the fundamental
principles of metabolism, for instance, and a recognition of the common
relationship between increased heat production, pulse rate, and certain
other symptoms are of the greatest help in deciding in what cases an
observation of the basal metabolism may be of diagnostic significance,
and in what cases it is entirely superfluous. It is much more important
to know in what particular case a determination of the basal metabolism
may be of value than it is to know the details of the performance of
the test. Then again, the physician should be able to interpret the
results of the test in the light of his individual patient. A basal
metabolism which is reported as 15 per cent above normal may or may not
be significant, and an electrocardiogram showing a prolonged conduction
time may be due to one of several factors, but in either case the
physician should not be forced to depend for the interpretation on the
man who does the laboratory work and who presumably has a less intimate
knowledge of the clinical condition of the patient. The clinician
himself should be able to appraise the laboratory findings if the
patient is to derive the greatest benefit.
It is frequently alleged that many of our medical schools and teaching
hospitals are producing “laboratory men” instead of clinicians. If it
is true that the graduates of these institutions enter the practice
of medicine handicapped by their dependence on the laboratory, then
the system of training is wrong or--what seems more probable--it is
imperfectly carried out. When schools and hospitals do their full
duty their graduates will have had an opportunity to study disease
intensively, checking and controlling their bedside observations by a
variety of exact laboratory investigations. Such an experience will
enable them to correlate the clinical manifestations of disease with
the underlying physiological processes, so that they can subsequently
understand and interpret disease without recourse to all the laboratory
procedures which were necessary in their student days. They will
enter practice trained so thoroughly in a limited number of simple
technical methods that they will not hesitate to use them, and they
will understand all of their significance. They will also know when
more complicated tests are indicated and how to interpret the results.
In spite of the extraordinary influence which the laboratory has had on
the development of medical science there is as yet no cause for the
physician to feel that he cannot keep up with the requirements of the
best modern practice. All of the more important elements are easily
within his grasp. The need in clinical medicine continues to be, not
for men trained in many laboratory methods but for men well grounded in
a few methods--not for better technicians, but for better clinicians.