Gold Standards

Question 1

DX of pharyngitis

Answer 1

throat culture (although rapid strep is done FIRST)

\+ = strep, bacterial (20% of pharyngitis cases)
- = viral (80% of pharyngitis)

Question 2

DX of alpha-thalassemias

Answer 2

DNA analysis of alpha gene probes

Question 3

DX of beta-thalassemias

Answer 3

Hb electrophoresis
dec HbA, inc HbA2, slight increase HbF = minor
usu normal HbA, usu normal HbA2, elevated HbF = major

Question 4

confirmatory for gout

Answer 4

joint aspirate >90% have monosodium urate crystals

Question 5

Lyme Disease

Answer 5

ELISA (high sens) and western blot (high spec)

Question 6

detecting osteomyelitis on imaging

Answer 6

MRI - high sens

Question 7

Osteoporosis DX and management

Answer 7

DEXA

osteoporosis is < -2.5
osteopenia is between -2.5 and -1

Question 8

dx of kyphosis

Answer 8

XR

Question 9

spondylolisthesis

Answer 9

XR (AP/lateral/oblique/flex/ext), MRI to rule out nerve root compression

Question 10

DX avascular necrosis of femoral head

Answer 10

XR > if inconclusive get an MRI which is most sens and spec

Question 11

detect patellar tracking abnormalities

Answer 11

XR > CT more sensitive than XR > MRI is the most sensitive

Question 12

spinal stenosis

Answer 12

CT myelogram, but CT/MRI would also reveal narrowing of spinal canal

Question 13

dx mortons neuroma

Answer 13

MRI (87 sen, 100 spec), XRays are normal

Question 14

dx osteochondroma

Answer 14

XR usu sufficient, can also biopsy

Question 15

dx of chondrosarcoma or ewings sarcoma

Answer 15

MRI. but XR and CT are both useful

XR and biopsy is choice for osteosarcoma (also has elevated ALP)

ewings has elevated LDH

Question 16

DX of encephalitis

Answer 16

brain biopsy 96% sens, 100% spec, but it is the most invasive

Question 17

dx of meningitis

Answer 17

lumbar puncture is required for definitive

Question 18

dx of pertussis

Answer 18

nasopharyngeal swab or aspirate cultured on *Regan-Lowe agar

Question 19

strep pharyngitis

Answer 19

throat swab culture 90-95% sensitivity

Question 20

investigation for CF

Answer 20

sweat chloride test

+ = > 60 in children and > 80 in adults

Question 21

dx RSV

Answer 21

viral culture - molecular probe is most sensitive

Question 22

dx of Hirschsprungs

Answer 22

rectal biopsy > see a lack of ganglion cells

Question 23

DX of appendicitis

Answer 23

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

Question 24

DX of ITP, hemophilia A, Von Willebrand’s disease

Answer 24

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.

Question 25

what is decreased in autoimmune atrophic gastritis.

Answer 25

Intrinsic factor

Question 26

Hepatitis B lab tests explained

HBeAg?
HBeAb?
HBsAg?
HBsAb IgG? IgM?

Answer 26

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.

Question 27

Explain the difference between a cohort study, case control study, RCCT, RCDBCT?

Answer 27

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.

Question 28

DX of Cushings?

Answer 28

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.

Question 29

DX of kidney stones

Answer 29

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.