Gold Standards Flashcards
DX of pharyngitis
throat culture (although rapid strep is done FIRST)
\+ = strep, bacterial (20% of pharyngitis cases) - = viral (80% of pharyngitis)
DX of alpha-thalassemias
DNA analysis of alpha gene probes
DX of beta-thalassemias
Hb electrophoresis
dec HbA, inc HbA2, slight increase HbF = minor
usu normal HbA, usu normal HbA2, elevated HbF = major
confirmatory for gout
joint aspirate >90% have monosodium urate crystals
Lyme Disease
ELISA (high sens) and western blot (high spec)
detecting osteomyelitis on imaging
MRI - high sens
Osteoporosis DX and management
DEXA
osteoporosis is < -2.5
osteopenia is between -2.5 and -1
dx of kyphosis
XR
spondylolisthesis
XR (AP/lateral/oblique/flex/ext), MRI to rule out nerve root compression
DX avascular necrosis of femoral head
XR > if inconclusive get an MRI which is most sens and spec
detect patellar tracking abnormalities
XR > CT more sensitive than XR > MRI is the most sensitive
spinal stenosis
CT myelogram, but CT/MRI would also reveal narrowing of spinal canal
dx mortons neuroma
MRI (87 sen, 100 spec), XRays are normal
dx osteochondroma
XR usu sufficient, can also biopsy
dx of chondrosarcoma or ewings sarcoma
MRI. but XR and CT are both useful
XR and biopsy is choice for osteosarcoma (also has elevated ALP)
ewings has elevated LDH
DX of encephalitis
brain biopsy 96% sens, 100% spec, but it is the most invasive
dx of meningitis
lumbar puncture is required for definitive
dx of pertussis
nasopharyngeal swab or aspirate cultured on *Regan-Lowe agar
strep pharyngitis
throat swab culture 90-95% sensitivity
investigation for CF
sweat chloride test
+ = > 60 in children and > 80 in adults
dx RSV
viral culture - molecular probe is most sensitive
dx of Hirschsprungs
rectal biopsy > see a lack of ganglion cells
DX of appendicitis
clinical, however an abdominal CT with contrast is the most sensitive imaging study for appendicitis (95–98% sensitive). Abdominal x-rays rarely help the diagnosis of appendicitis. Ultrasound is also a very useful diagnostic choice
DX of ITP, hemophilia A, Von Willebrand’s disease
In idiopathic thrombocytopenic purpura, a platelet-associated IgG test is positive.
Factor VIII is decreased in hemophilia A.
Von Willebrand’s factor is decreased in Von Willebrand’s disease.
what is decreased in autoimmune atrophic gastritis.
Intrinsic factor
Hepatitis B lab tests explained
HBeAg?
HBeAb?
HBsAg?
HBsAb IgG? IgM?
The detection of the hepatitis B envelope antigen (HBeAg) is a sign of chronic hepatitis B infection with a high infectivity and a poor chance of spontaneous resolution. If the hepatitis B envelope antibody (HBeAb) is detected, this is a sign of low infectivity and a good prognosis. The hepatitis B surface antigen (HBsAg) is the first Ag that arises in acute hep B infection, and can be present in the incubation period. People who have had a hepatitis B vaccine, or who have had a past infection, will show immunity with detectable HBsAb IgG. The hepatitis B core antibody IgM and IgG is elevated during the convalescence period between clearance of the surface antigen and development of the surface antibody.
Explain the difference between a cohort study, case control study, RCCT, RCDBCT?
a cohort study, in which a group of people with a common characteristic are exposed to a toxin or medicine and observed over time to see the outcome. It is similar to a case control study, in which a group of people with a disease, and a control group (without the disease), are both observed over time to see if certain factors differ between the two groups. An example of a case control study is the association between tobacco smoking and lung cancer, as demonstrated by the retrospective observation of a group of people with lung cancer versus a group without lung cancer, and the recognition that the lung cancer group had a significant smoking history. The main difference between a cohort study and a case control study is that in a cohort study, all of the subjects have the same disease (or other characteristic, such as being born in the same location or in the same year). In a case control study, the “case” group has a specific disease, and the control group does not. A randomized controlled clinical trial (RCCT) is a prospective, experimental study involving a treatment group and a control group; randomization of the assignment of treatment and control groups helps to minimize bias. In a randomized controlled double-blind clinical trial, the same methods apply as for a RCCT, and in addition, neither the researchers nor the subjects are aware of the group assignment.
DX of Cushings?
This is a case of Cushing’s syndrome, which can be diagnosed with 4 accepted methods: urinary free cortisol, a low-level dexamethasone suppression test, evening salivary and serum cortisol, and a dexamethasone-CRH test. If the patient has Cushing’s syndrome, due to an adrenal tumor or exogenous corticosteroid use, cortisol will be elevated. Urinary free cortisol evaluates cortisol secretion over a 24 hour period, and therefore is very useful as an initial screening test. A low-level dexamethasone suppression test mimics the action of the pituitary gland, which should decrease ACTH production in the presence of elevated cortisol. In Cushing’s syndrome, pituitary ACTH is not suppressed by dexamethasone, and cortisol remains elevated.
DX of kidney stones
Currently, the noncontrast helical CT is the gold standard for evaluating kidney stones, however, of the options listed, plain abdominal radiography would be the best answer. Plain abdominal radiographs are useful in detecting radiopaque nephrolithiasis (calcium phosphate and calcium oxalate) and can be more accurate than CT in determining stone size and shape. MRI is not typically useful in evaluation of nephrolithiasis. Tomography may be useful in elucidating stones not clearly seen in other studies, however plain film (KUB) is a more correct answer. Nuclear imaging takes an extensive period of time and is typically not widely available.
