Introducción a la evaluación de pruebas diagnósticas y preguntas sobre diagnóstico en las guías de práctica clínica

1. Las pruebas
diagnósticas en las GPC
De la evidencia a la recomendación
Carlos Cuello, MD

2. Escenario
• Estás
llevando
a
cabo
la
GPC
de
trauma
craneal
en
pediatría
• Llegas
a
la
sección
de
diagnóstico

3. Opciones
para
gradar
la
evidencia
y
recomendaciones
• CEBM
• NICE
• SIGN
• GRADE
• USPSTF

4. CEBM

5. Level Evidence
SR (with homogeneity*) of Level 1 diagnostic studies; CDR† with 1b studies from different clinical
1a
centres
Validating** cohort study with good††† reference standards; or CDR† tested within one clinical
1b
centre
1c Absolute SpPins and SnNouts††
2a SR (with homogeneity*) of Level >2 diagnostic studies
Exploratory** cohort study with good††† reference standards; CDR† after derivation, or validated
2b
only on split-sample§§§ or databases
3a SR (with homogeneity*) of 3b and better studies
3b Non-consecutive study; or without consistently applied reference standards
4 Case-control study, poor or non- independent reference standard
Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first
5
principles"

6. CEBM
-­‐
OXFORD
GRADOS'DE'RECOMENDACIÓN'
A " "Estudios"nivel"1"con"consistencia" "
B " "
"Estudios"nivel"2"ó"3"con"consistencia"o"extrapolaciones"de"estudios"nivel"1"
C " "
"Estudios"nivel"4"o"extrapolaciones"de"estudios"nivel"2"ó"3"
D " "Evidencia"nivel"5"o"estudios""problemá?cos,"con"inconsistencias"o"evidencia"
inconclusa"de"cualquier"nivel "

7. NICE

10. SIGN
• Cambios
se
vienen
• Utiliza
actualmente
sus
tablas
de
intervenciones
• Probablemente
se
adapte
al
GRADE

11. are discussed in section 5.
agnosis and management of colorectal cancer
7.1 POPULATION SCREENING
Population based trials of guaiac based faecal occult blood testing (FOBT) have consistently demonstrated
The guaiac reductions in colorectal cancer mortality andcreates a problemin a meta-analysis that indicates ++
significant test, however, is not specific for blood which are summarised with sensitivity and specificity.17
a reduction of 16% overall trial compared the guaiac FOBT with uptake.16 The majority testing reported 1
One randomised controlledand 25% when adjusted for screeningfaecal immunochemical of trials (FIT) over
one round, with the FIT set at an analytical sensitivity that gave may have caused stress or anxiety forthat of 1+
that the positive predictive value of the tests were low,16 which a positivity rate approximately twice those
receiving a false-positive result.
the guaiac test.17 This study demonstrated that participation and detection rates for advanced adenomas
and cancer were significantly higher for FIT compared with guaiac FOBT but that FIT generated more than
twice as many colonoscopies.17 |7
A multicentre randomised controlled trial (RCT) of single flexible sigmoidoscopy in a population aged between
55 and 64 who had expressed an interest in this type of screening demonstrated a significant reduction in
both colorectal cancer mortality and incidence which was maintained for up to 12 years, although no effect 1++
on the incidence of right-sided cancer was seen.18 Owing to the selected population, this was an efficacy
study and the performance of flexible sigmoidoscopy as a population screening tool will be dependent on
uptake by an unselected population.
Although FIT and flexible sigmoidoscopy may have advantages over guaiac FOBT, how these tests would
perform in the Scottish population is not yet clear.
No evidence was identified to support colonoscopy or computed tomography colonography as a primary
screening modality.
It is important to acknowledge that no screening modality is 100% sensitive, and that the guaiac FOBT has
been shown to be associated with a substantial interval cancer rate.19
A Population screening for colorectal cancer using the guaiac FOBT should continue in the Scottish
population until further evidence on other modalities is available.
A negative guaiac FOBT result is not a guarantee that no colorectal cancer is present and should not
impact on the need to investigate symptoms.

12. Grading of Recommendations Assessment, Development and Evaluation

13. ¿Por
qué
hacer
pruebas
diagnósticas
• Identificar
alteraciones
de
la
fisiología
humana
• Establecer
un
pronóstico
• Monitorizar
el
curso
de
una
enfermedad
o
la
respuesta
a
un
tratamiento
• Aumentar
la
certeza
de
la
presencia
o
ausencia
de
enfermedad

14. Pruebas
diagnósticas
• Dicotómicas
• Categóricas
• Continuas

15. El
sistema
GRADE

16. Investigar
el
campo
• Un
panel
de
una
GPC
debe
investigar
primero
¿Cuál
es
el
camino
que
toman
los
clínicos
para
esta
condición?
-­‐ Prueba
diagnóstica
actual
-­‐ Serie
de
pruebas
diagnósticas
-­‐ No
hay
pruebas
diagnósticas
para
esta
condición

17. Una
prueba
nueva
puede
funcionar
como
• Triage
(o
de
escrutinio)
• De
reemplazo
• Adición
a
un
proceso
diagnóstico

18. La
pregunta
PICO
P Lactantes con sospecha de infección urinaria
La detección de bacterias en orina con la tinción
I
Gram
C con el examen general de orina sin la tinción
evita el uso de antibióticos?
O evita el urocultivo? discutan
...

19. Outcomes
• OJO:
los
valores
diagnósticos
(sensibilidad,
especificidad,
VPP,
VPN,
etc.)
son
desenlaces
subrogados
• ¿Cuáles
serían
desenlaces
importantes
para
el
paciente?

20. Identifica
la
evidencia
• De
preferencia
en
revisiones
sistemáticas
• Busca
ensayos
clínicos
aleatorios
sobre
una
prueba
diagnóstica)
y
que,
de
preferencia,
evalúe
un
desenlace
importante
para
el
paciente
• Lo
más
probable
es
que
no
lo
encuentres
:(

21. Evalúa
la
calidad
de
la
evidencia
• ¿Qué
diseño
de
estudio
es?
• ¿Qué
factores
pueden
disminuir
la
calidad
de
la
evidencia?

22. Disminuyen
la
calidad
de
la
evidencia
• El
diseño
o
ejecución
del
estudio
(riesgo
de
sesgo)
• Evidencia
indirecta
• Inconsistencias
• Imprecisión
• Sesgo
de
publicación

23. Riesgo
de
sesgo
• En
cuanto
al
diseño
del
estudio:
-­‐ Estudios
de
diagnóstico
(transversales
o
cohortes)
en
pacientes
con
incertidumbre
diagnóstica
y
comparación
directa
de
los
resultados
de
las
pruebas
con
un
adecuado
estándar
de
oro,
serán
catalogados
como
de
alta
calidad
-­‐ Estos
estudios,
sin
embargo,
son
raros
de
encontrar

24. QUADAS
assessment if it is impossible for any studies to meet a particular quality criterion. In such
instances it is essential to report that all studies were at risk of the associated bias.
Quality
criteria
of
Diagnostic
Accuracy
Studies
Table 9.1 Recommended quality items derived from QUADAS tool (Whiting 2003)
1. Was the spectrum of patients representative of the patients who will receive the test in
practice? (representative spectrum)
2. Is the reference standard likely to classify the target condition correctly? (acceptable
reference standard)
3. Is the time period between reference standard and index test short enough to be
reasonably sure that the target condition did not change between the two tests?
(acceptable delay between tests)
4. Did the whole sample or a random selection of the sample, receive verification using the
intended reference standard? (partial verification avoided)
5. Did patients receive the same reference standard irrespective of the index test result?
(differential verification avoided)
6. Was the reference standard independent of the index test (i.e. the index test did not form
part of the reference standard)? (incorporation avoided)
7. Were the reference standard results interpreted without knowledge of the results of the
index test? (index test results blinded)
8. Were the index test results interpreted without knowledge of the results of the reference
standard? (reference standard results blinded)
9. Were the same clinical data available when test results were interpreted as would be
available when the test is used in practice? (relevant clinical information)
10. Were uninterpretable/ intermediate test results reported? (uninterpretable results
reported)
11. Were withdrawals from the study explained? (withdrawals explained)

25. Evidencia
indirecta
• Similar
a
los
estudios
de
tratamiento
• Estudios
que
proveen
solo
de
sensibilidad
y
especificidad,
proveen
de
evidencia
indirecta
• En
este
caso,
usualmente
queda
en
“low
quality”

26. Evidencia
indirecta
• También
se
puede
disminuir
la
calidad
por
diferencias:
-­‐ entre
la
población
en
estudio
y
a
la
que
se
aplicaría
la
prueba
en
la
vida
real
-­‐ entre
la
experiencia
de
los
sujetos
en
el
estudio
y
los
que
usarían
la
prueba
en
la
vida
real
• Si
comparas
dos
pruebas
diagnósticas
entre
ellas,
que
usan
un
solo
estándar
de
oro,
pero
en
dos
estudios
separados
(para
c/u),
es
evidencia
indirecta

27. Inconsistencia
• Igual
que
en
estudios
de
tratamientos
• Disimilitudes
en
la
sensibilidad,
especificidad,
LRs

28. Imprecisión
• Amplios
intervalos
de
confianza

29. Sesgo
de
publicación
• Si
existe
solo
un
estudio
con
muy
poco
tamaño
de
muestra
• Asimetría
en
“funnel
plots”
(gráficos
de
embudo)

30. Gracias