RAT1

Question 1

Which of the following statements regarding radiological studies is FALSE?

A. CT scans use x-rays to generate an image of the human body.
B. Ultrasoud scans can assess direction of blood flow using the Doppler effect.
C. Muscles and blood have different observable densities on radiographs.
D. MRI scans do not use ionising radiation to generate images.
E. CT scan studies typically take a shorter time to perform than MRI scans.

RAT 1 practice quiz Q1

Answer 1

C. Muscles and blood have different observable densities on radiographs.

Muscles and blood have similar (soft tissue) density on conventional radiography and cannot be differentiated on such studies.

Question 2

Which is the classical ratio of aspartate aminotransferase (AST) over alanine aminotransferase (ALT) in alcoholic hepatitis?

A. 1:1
B. Less than or equals to 1:2
C. 1.5:1
D. 5:1
E. More than or at least 2:1

RAT 1 practice quiz Q2

Answer 2

E. More than or at least 2:1

The reasons for a classical excess of serum AST activity compared to serum ALT activity in alcoholic hepatitis have been attributed to:
(i) decreased ALT activity most likely due to B6 depletion in the livers of alcoholics,
(ii) mitochondrial damage leading to increased release of mitochondrial AST in serum. This is supported by the finding that normally most of the AST activity in serum is the cytosolic isoenzyme, however in alcoholism, mitochondrial AST is prefernetially released.

Question 3

A test with high sensitivity will not miss many patients who have the disease. The sensitivity of a clinical laboratory test is defined as the number of true positive test results divided by the sum of true positive and fale negative test results. What does ‘sensitivity’ mean in this context?

A. Sensitivity is the probability that a disease-free individual will test negative.
B. Sensitivity is the probability of being disease-free, given a negative result.
C. Sensitivity is the same as precision.
D. Sensitivity is the probability that an individual with the disease will test positive.
E. Sensitivity is the probability of having a disease, given a positive test result.

RAT 1 practice quiz Q3

Answer 3

D. Sensitivity is the probability that an individual with the disease will test positive.

• Sensitivity is the probability of getting a positive result in a diseased patient.
• Specificity is the probability of getting a negative result in a disease-free individual.
• Precision refers to the closeness of measurements that are repeated under similar conditions.
• Positive predictive value and negative predictive value are used to describe the probability of the presence/absence of a disease given a test result.
• PPV = probability of having a disease, given a positive test result.
• NPV = probability of being disease-free, given a negative test result.

Question 4

In the treatment of dehydration due to vomitting in gastric outlet obstruction, which of the following best describes the benefit of using intravenous 0.9% NaCl solution for fluid replacement?

A. Increase exchange of Na+ and H+ at the collecting ducts in the kidney.
B. Increase reabsorption of HCO3- in the collecting ducts in the kidney.
C. Increase Cl- loss through the kidneys.
D. Increase exchange of Cl- and HCO3- by the Type B intercalated cells.
E. Hydration of interstitial space.

RAT 1 practice quiz Q4

Answer 4

D. Increase exchange of Cl- and HCO3- by the Type B intercalated cells.

Vomitting leads to loss of chloride from the gastric fluids, leading to hypochloraemia metabolic alkalosis. Hypochloraemia drives further metabolic alkalosis in the kidneys due to decreased reabsorption of chloride in exchange for secretion of HCO3- in the Type B cells (i.e. less HCO3- secreted). Replacement of the fluid losses with chloride containing fluids like normal saline corrects the metabolic alkalosis by increasing the gradient for chloride reabsorption, thus facilitating chloride reabsorption and HCO3- excretion.

Question 5

A mu receptor antagonist medication is studied for its effect in reversing the gastrointestinal motility effect of opoid. What property will limit its movement across the blood brain barrier?

A. Presence of a quaternary amine.
B. Being in a unionized state.
C. Presence of a tertiary amine.
D. Presence of a secondary amine.
E. Presence of an ester bond.

RAT 1 practice quiz Q5

Answer 5

A. Presence of a quaternary amine.

Quaternary amines are permanently charged and are poorly lipid soluble, and these features lead to poor CNS penetration.