Family Practice
Vol. 8, No. 4
© Oxford University Press 1991
Printed in Great Britain
Medical Decision Making By General Practitioners and Specialists JA KNOTTNERUS
INTRODUCTION General practice in the United Kingdom and the Netherlands has deep roots in history and society;1 with increasing specialization and complexity of care, the importance of a generalist approach to health problems can only increase. For this reason, the professionals involved must have a good understanding and appreciation of one another's situation and the specific characteristics of their medical decision making. Unfortunately, in health care policy the key position of the GP does not always seem to be appreciated. However, for maintaining coherent health care, a clear recognition of principles and differences of the medical decision making of GPs and specialists is indispensible.
behaviour, and thus he has extra points of reference as regards risks and the probability and prognosis of particular disorders.7 For patients with chronic disease, the GP has a permanent responsibility in giving medical and personal support, while the specialist's involvement is specific and temporary. PROBLEM SPACE AND DIAGNOSTIC RANGE From their large problem space, GPs often have to draw up rather general diagnostic hypotheses: inflammation, malignancy, stress, or even 'organic/nonorganic' or 'pathology/no pathology'. This assessment is related to probability, severity and consequences and may or may not lead the doctor to look for a relevant disorder. Specialists are in a position to formulate more specific hypotheses, because of the GP's preparatory work and his reason for referral. Even in the assessment of identical case histories specialists more often formulate hypotheses about rare and serious organic disorders, while GPs tend to consider more psychosomatic problems.8-9 In view of a relatively large problem space, the GP needs diagnostics with a wide 'diagnostic range', to be applied even before specific hypotheses can be formulated. Thus, a broad spectrum of diagnostic possibilities can be scanned. Examples are questions about general well-being, weight changes and the development of the complaints over time, and tests such as the erythrocyte sedimentation rate.10 Time also may be used as a diagnostic prospectively, in cases where non-specific complaints might hide serious disorders but also an innocent, temporary indisposition. Sooner than the GP, the specialist will require diagnostics aimed at clearly defined hypotheses. Internists do not only apply more diagnostic tests, but also use more specific clinical-chemical parameters such as renal function, liver function and electrolytes.9 A topical matter is whether some diagnostic methods, such as cytological puncturing and gastrointestinal endoscopy, should be directly available to the GP. However, a first 'broad screening' using simple methods is often more important for reducing the
SPECTRUM OF HEALTH PROBLEMS The GP is confronted with a fundamentally different pattern of complaints and disorders than the specialist.2-3
The GP sees patients whose problems have not yet been reduced to a specific category. The 'problem space' is large, especially in cases of 'vague symptoms'. Patients seen by the specialist have usually been selected with respect to specialism or even diagnosis. Given particular complaints, serious diseases are less frequent among patients visiting their GP than among those who have been referred to a specialist.4-* The GP sees more patients in whom somatic complaints hide psychological and social problems. The GP usually encounters serious disorders at an earlier, less developed stage. Accordingly, the recognition of these disorders is more difficult for the GP. In general practice, a particular disease will, by and large, have a more favourable prognosis and be more amenable to treatment than in specialist practice, since the more difficult and intractable cases are referred. The GP more often has prior knowledge on the patient, his social situation and his care-seeking Dep»rtment of General Practice, Univerjity of Umburg, P.O. Box 616, 6200 M D Maastricht. The Netherlands.
305
Downloaded from http://fampra.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 4, 2015
Knottnerus JA. Medical decision making by general practitioners and specialists. Family Practice 1991; 8; 305-307.
306 FAMILY PRACTICE—AN GP's problem space than specific tests he may want to carry out later. At the same time, where the problem space is larger, it is more difficult to formulate diagnostic strategies than in the phase where the problem has been reduced to a small number of clearly defined hypotheses. Therefore, general protocols and algorithms are more difficult to define in general practice than in many specialties.
results or symptoms, will show abnormal results more often.13 In other words: in general practice, sick subjects resemble healthy subjects, while in specialized practice healthy subjects resemble those with disease (or they would not have been referred!). The likelihood ratio may even be lower in specialized practice, especially for tests and symptoms which are important for the decision to refer. Part of their discrimination has been 'used up' by the referring GP. Such diagnostics yield more information in general practice than in specialized practice. In conclusion, the discrimination of tests to be applied in general practice can best be determined in patients not yet selected by referral.13'14 TREATMENT AND PROGNOSIS Preselection by the GP confronts the specialist with a different patient population with many prognostically unfavourable cases. Therefore he is forced to use more drastic therapies, which nevertheless may lead to poorer outcomes. He also needs additional investigations more often. Problems arise when specialists forget this preselection, and teach GPs on the basis of their hospital experience, in clinical sessions or textbooks. This may lead to 'overshooting' with respect to diagnostic and therapeutic interventions. Selection with respect to prognosis and susceptibility to therapy should also be taken into account in generalizing the results of randomized experiments, however well designed and executed. As such experiments are often done in specialized centres, the outcomes cannot simply be applied to general practice. More research into the effectiveness of therapeutic interventions should be done in a general practice setting. Furthermore, GP and specialist should develop a consensus about indications for referral. THE GATEKEEPING FUNCTION, OR THE GP AS EQUILIBRIST One of the most important skills for the GP is differentiating between patients who need further examination, treatment or referral, and those who do not. GPs deal with 85-90% of the presented illness episodes on their own, i.e. without referral. It is of vital importance that the GP's gatekeeping function is not unjustly discredited. Let us elaborate an hypothetical example. In Table la it can be seen that of those patients with a particular complaint X who were in need of specialized treatment, GPs referred 90% without undue delay: the sensitivity of their referral behaviour is 90%. As 10% of those patients with complaint X who did not need specialized treatment were nevertheless referred, the specificity of the referral behaviour is 100%-10% = 90%. The likelihood ratio is 90%/10% = 9. So, GPs do achieve a fairly high discrimination, compared to many individual diagnostic tests." Specialists who wish to provide feedback to GPs will urge them to reduce the number of patients (bottom left) who are initially missed and who reach the specialist 'too late'. There will be far less attention for
Downloaded from http://fampra.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 4, 2015
'DISCRIMINATION' AND PREDICTIVE VALUE The value of diagnostic tests is determined primarily by their discriminatory power, characterized by sensitivity, specificity and likelihood ratio (test characteristics)." Unfortunately, the discriminatory power of many tests has hardly been investigated, particularly in general practice.12'13 Assessment of history is very important. For example, complaints of typical angina pectoris are highly informative, and more sophisticated tests add little to this.11 History taking and physical examination may yield certain 'crucial' findings, which are of the greatest importance to the GP. The predictive value of diagnostic information depends on the prior probability of disease."-13 In this respect, the diagnostic positions of general practitioners and specialists may be characterized as follows. As a result of preselection by the GP, the prior probability (prevalence) of disorders requiring specialist care is higher among referred patients than among patients seen by the GP. Consequently, the predictive value of a particular abnormal finding is greater in specialist practice. By contrast, the predictive value of a normal test result for the absence of such disorders is greater in general practice. For diseases which are more often seen by the GP, the situation is the opposite. Examples are exanthemas in children, uncomplicated urinary tract infections and vaginal discharge, and functional abdominal complaints. Comparing the clinical performance of GPs and specialists, a higher prior probability in the referred population might erroneously suggest that the specialist is a better examiner, even if the discrimination of the examinations is the same for both. Absence of the preselection by the GP would result in many superfluous diagnostic tests, and perhaps therapeutic interventions. The prior probability of diseases is also important in choosing or recommending strategies. A certain diagnostic strategy might be optimal for the specialist, while for the general practitioner the risk of false positive findings is too high. On the other hand, the specialist might produce too many false negative results following a less aggressive, expectant strategy that would be suitable for the GP.13 Even the discrimination of tests itself may change as a result of referral to the specialist: sensitivity will often be higher in specialist practice as a consequence of selection: diseased subjects show positive results more often than in general practice, especially in cases with a more developed symptomatology. Specificity, on the other hand, will be lower in specialist practice: healthy subjects, referred because of suspicious test
INTERNATIONAL JOURNAL
MEDICAL DECISION MAKING TABLE 1 The general practitioners gateketping function: referral behaviour of GP's in relation to the necessity of immediate specialist treatment, in 1000 patients with a pattern of complaints X a. Original situation Specialist treatment Not Necessary Necessary Total 90
90
180
10 100
810 900
820 1000
prior probability of disease requiring specialist treatment = 100/1000=10%. sensitivity of referral behaviour = 90/100 = 90% specificity of referral behaviour = 810/900 = 90% likelihood ratio of referral behaviour = 90%/(100% - 90%) = 9 predictive value of referral = 90/180 = 50% b. Situation after halving the number of false-negatives Specialist treatment Not Necessary Necessary Total immediately referred not, or not immediately referred total
95
495
590
5 100
405 900
410 1000
bottom left category. In the end, all 1000 patients will be immediately referred, the GP's gatekeeping function has completely disappeared, and the problem of distinguishing between the two categories has been shifted entirely to the specialist. However, the specialist lacks the all-round expertise of the GP, and many diagnostic hypotheses are outside his scope. What if all patients with unexplained fatigue, which may indicate hypothyroidism but usually result from non-somatic problems, were immediately referred to the endocrinologist! Additional, often unnecessary investigations and treatments will put a great strain on specialist, patients and society. Clearly, general practice is a cornerstone of our health care system. The training of, and scientific backup for this equilibrist, who balances between the 'disciplinary committee category' (bottom left) and the 'medicalisation category' (top right), is a sine qua non. 1
2
3
4
3
sensitivity of referral behaviour = 95/100°95% specificity of referral behaviour = 405/900 = 45% likelihoodratioof referral behaviour = 95%/(100%-45%) = 1.7 predictive value of referral = 95/590= 16%
6
patients who were referred correctly and in time (the top left-hand category) and for those who have been unnecessarily referred (top right). No attention at all is given to those who were not referred and did not need to be (bottom right); this category is of no concern to the specialist, although it highlights one of the primary tasks of the GP: preventing unnecessary referrals. Suppose, that the exaggerated attention given to the bottom left group leads to a new situation in which five of the 10 patients in this group are immediately referred. Since the symptoms do not allow these patients to be distinguished from those in the bottom right category, half of the 810 patients who originally ended up here will now also be immediately referred (Table lb)! The sensitivity of the referral increases from 90 to 95%, but the specificity decreases from 90 to 45%! The likelihood ratio is reduced from 9 to 1.7, and the predictive value has decreased from 50 to 16
Vol. 8, No. 4
© Oxford University Press 1991
Printed in Great Britain
Medical Decision Making By General Practitioners and Specialists JA KNOTTNERUS
INTRODUCTION General practice in the United Kingdom and the Netherlands has deep roots in history and society;1 with increasing specialization and complexity of care, the importance of a generalist approach to health problems can only increase. For this reason, the professionals involved must have a good understanding and appreciation of one another's situation and the specific characteristics of their medical decision making. Unfortunately, in health care policy the key position of the GP does not always seem to be appreciated. However, for maintaining coherent health care, a clear recognition of principles and differences of the medical decision making of GPs and specialists is indispensible.
behaviour, and thus he has extra points of reference as regards risks and the probability and prognosis of particular disorders.7 For patients with chronic disease, the GP has a permanent responsibility in giving medical and personal support, while the specialist's involvement is specific and temporary. PROBLEM SPACE AND DIAGNOSTIC RANGE From their large problem space, GPs often have to draw up rather general diagnostic hypotheses: inflammation, malignancy, stress, or even 'organic/nonorganic' or 'pathology/no pathology'. This assessment is related to probability, severity and consequences and may or may not lead the doctor to look for a relevant disorder. Specialists are in a position to formulate more specific hypotheses, because of the GP's preparatory work and his reason for referral. Even in the assessment of identical case histories specialists more often formulate hypotheses about rare and serious organic disorders, while GPs tend to consider more psychosomatic problems.8-9 In view of a relatively large problem space, the GP needs diagnostics with a wide 'diagnostic range', to be applied even before specific hypotheses can be formulated. Thus, a broad spectrum of diagnostic possibilities can be scanned. Examples are questions about general well-being, weight changes and the development of the complaints over time, and tests such as the erythrocyte sedimentation rate.10 Time also may be used as a diagnostic prospectively, in cases where non-specific complaints might hide serious disorders but also an innocent, temporary indisposition. Sooner than the GP, the specialist will require diagnostics aimed at clearly defined hypotheses. Internists do not only apply more diagnostic tests, but also use more specific clinical-chemical parameters such as renal function, liver function and electrolytes.9 A topical matter is whether some diagnostic methods, such as cytological puncturing and gastrointestinal endoscopy, should be directly available to the GP. However, a first 'broad screening' using simple methods is often more important for reducing the
SPECTRUM OF HEALTH PROBLEMS The GP is confronted with a fundamentally different pattern of complaints and disorders than the specialist.2-3
The GP sees patients whose problems have not yet been reduced to a specific category. The 'problem space' is large, especially in cases of 'vague symptoms'. Patients seen by the specialist have usually been selected with respect to specialism or even diagnosis. Given particular complaints, serious diseases are less frequent among patients visiting their GP than among those who have been referred to a specialist.4-* The GP sees more patients in whom somatic complaints hide psychological and social problems. The GP usually encounters serious disorders at an earlier, less developed stage. Accordingly, the recognition of these disorders is more difficult for the GP. In general practice, a particular disease will, by and large, have a more favourable prognosis and be more amenable to treatment than in specialist practice, since the more difficult and intractable cases are referred. The GP more often has prior knowledge on the patient, his social situation and his care-seeking Dep»rtment of General Practice, Univerjity of Umburg, P.O. Box 616, 6200 M D Maastricht. The Netherlands.
305
Downloaded from http://fampra.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 4, 2015
Knottnerus JA. Medical decision making by general practitioners and specialists. Family Practice 1991; 8; 305-307.
306 FAMILY PRACTICE—AN GP's problem space than specific tests he may want to carry out later. At the same time, where the problem space is larger, it is more difficult to formulate diagnostic strategies than in the phase where the problem has been reduced to a small number of clearly defined hypotheses. Therefore, general protocols and algorithms are more difficult to define in general practice than in many specialties.
results or symptoms, will show abnormal results more often.13 In other words: in general practice, sick subjects resemble healthy subjects, while in specialized practice healthy subjects resemble those with disease (or they would not have been referred!). The likelihood ratio may even be lower in specialized practice, especially for tests and symptoms which are important for the decision to refer. Part of their discrimination has been 'used up' by the referring GP. Such diagnostics yield more information in general practice than in specialized practice. In conclusion, the discrimination of tests to be applied in general practice can best be determined in patients not yet selected by referral.13'14 TREATMENT AND PROGNOSIS Preselection by the GP confronts the specialist with a different patient population with many prognostically unfavourable cases. Therefore he is forced to use more drastic therapies, which nevertheless may lead to poorer outcomes. He also needs additional investigations more often. Problems arise when specialists forget this preselection, and teach GPs on the basis of their hospital experience, in clinical sessions or textbooks. This may lead to 'overshooting' with respect to diagnostic and therapeutic interventions. Selection with respect to prognosis and susceptibility to therapy should also be taken into account in generalizing the results of randomized experiments, however well designed and executed. As such experiments are often done in specialized centres, the outcomes cannot simply be applied to general practice. More research into the effectiveness of therapeutic interventions should be done in a general practice setting. Furthermore, GP and specialist should develop a consensus about indications for referral. THE GATEKEEPING FUNCTION, OR THE GP AS EQUILIBRIST One of the most important skills for the GP is differentiating between patients who need further examination, treatment or referral, and those who do not. GPs deal with 85-90% of the presented illness episodes on their own, i.e. without referral. It is of vital importance that the GP's gatekeeping function is not unjustly discredited. Let us elaborate an hypothetical example. In Table la it can be seen that of those patients with a particular complaint X who were in need of specialized treatment, GPs referred 90% without undue delay: the sensitivity of their referral behaviour is 90%. As 10% of those patients with complaint X who did not need specialized treatment were nevertheless referred, the specificity of the referral behaviour is 100%-10% = 90%. The likelihood ratio is 90%/10% = 9. So, GPs do achieve a fairly high discrimination, compared to many individual diagnostic tests." Specialists who wish to provide feedback to GPs will urge them to reduce the number of patients (bottom left) who are initially missed and who reach the specialist 'too late'. There will be far less attention for
Downloaded from http://fampra.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 4, 2015
'DISCRIMINATION' AND PREDICTIVE VALUE The value of diagnostic tests is determined primarily by their discriminatory power, characterized by sensitivity, specificity and likelihood ratio (test characteristics)." Unfortunately, the discriminatory power of many tests has hardly been investigated, particularly in general practice.12'13 Assessment of history is very important. For example, complaints of typical angina pectoris are highly informative, and more sophisticated tests add little to this.11 History taking and physical examination may yield certain 'crucial' findings, which are of the greatest importance to the GP. The predictive value of diagnostic information depends on the prior probability of disease."-13 In this respect, the diagnostic positions of general practitioners and specialists may be characterized as follows. As a result of preselection by the GP, the prior probability (prevalence) of disorders requiring specialist care is higher among referred patients than among patients seen by the GP. Consequently, the predictive value of a particular abnormal finding is greater in specialist practice. By contrast, the predictive value of a normal test result for the absence of such disorders is greater in general practice. For diseases which are more often seen by the GP, the situation is the opposite. Examples are exanthemas in children, uncomplicated urinary tract infections and vaginal discharge, and functional abdominal complaints. Comparing the clinical performance of GPs and specialists, a higher prior probability in the referred population might erroneously suggest that the specialist is a better examiner, even if the discrimination of the examinations is the same for both. Absence of the preselection by the GP would result in many superfluous diagnostic tests, and perhaps therapeutic interventions. The prior probability of diseases is also important in choosing or recommending strategies. A certain diagnostic strategy might be optimal for the specialist, while for the general practitioner the risk of false positive findings is too high. On the other hand, the specialist might produce too many false negative results following a less aggressive, expectant strategy that would be suitable for the GP.13 Even the discrimination of tests itself may change as a result of referral to the specialist: sensitivity will often be higher in specialist practice as a consequence of selection: diseased subjects show positive results more often than in general practice, especially in cases with a more developed symptomatology. Specificity, on the other hand, will be lower in specialist practice: healthy subjects, referred because of suspicious test
INTERNATIONAL JOURNAL
MEDICAL DECISION MAKING TABLE 1 The general practitioners gateketping function: referral behaviour of GP's in relation to the necessity of immediate specialist treatment, in 1000 patients with a pattern of complaints X a. Original situation Specialist treatment Not Necessary Necessary Total 90
90
180
10 100
810 900
820 1000
prior probability of disease requiring specialist treatment = 100/1000=10%. sensitivity of referral behaviour = 90/100 = 90% specificity of referral behaviour = 810/900 = 90% likelihood ratio of referral behaviour = 90%/(100% - 90%) = 9 predictive value of referral = 90/180 = 50% b. Situation after halving the number of false-negatives Specialist treatment Not Necessary Necessary Total immediately referred not, or not immediately referred total
95
495
590
5 100
405 900
410 1000
bottom left category. In the end, all 1000 patients will be immediately referred, the GP's gatekeeping function has completely disappeared, and the problem of distinguishing between the two categories has been shifted entirely to the specialist. However, the specialist lacks the all-round expertise of the GP, and many diagnostic hypotheses are outside his scope. What if all patients with unexplained fatigue, which may indicate hypothyroidism but usually result from non-somatic problems, were immediately referred to the endocrinologist! Additional, often unnecessary investigations and treatments will put a great strain on specialist, patients and society. Clearly, general practice is a cornerstone of our health care system. The training of, and scientific backup for this equilibrist, who balances between the 'disciplinary committee category' (bottom left) and the 'medicalisation category' (top right), is a sine qua non. 1
2
3
4
3
sensitivity of referral behaviour = 95/100°95% specificity of referral behaviour = 405/900 = 45% likelihoodratioof referral behaviour = 95%/(100%-45%) = 1.7 predictive value of referral = 95/590= 16%
6
patients who were referred correctly and in time (the top left-hand category) and for those who have been unnecessarily referred (top right). No attention at all is given to those who were not referred and did not need to be (bottom right); this category is of no concern to the specialist, although it highlights one of the primary tasks of the GP: preventing unnecessary referrals. Suppose, that the exaggerated attention given to the bottom left group leads to a new situation in which five of the 10 patients in this group are immediately referred. Since the symptoms do not allow these patients to be distinguished from those in the bottom right category, half of the 810 patients who originally ended up here will now also be immediately referred (Table lb)! The sensitivity of the referral increases from 90 to 95%, but the specificity decreases from 90 to 45%! The likelihood ratio is reduced from 9 to 1.7, and the predictive value has decreased from 50 to 16
