A new biochemical marker has been found which is increased in mothers who are carrying fetuses with Down's syndrome. The new blood test is trialled in 1,000 women over the age of 35 years. Of these women 20 were found to be carrying a fetus with Down's syndrome as assessed using standard measures. The new test was positive in 15 of the 20 cases but was also positive in 30 of the remaining 980 women.
What is the positive predictive value of the test?
Correct Answer C:
A contingency table can be constructed from the above data, as shown below:
Positive predictive value = TP / (TP + FP) = 15 / (15 + 30) = 0.33
It would be unusual for a medical exam not to feature a question based around screening test statistics. The available data should be used to construct a contingency table as below:
TP = true positive; FP = false positive; TN = true negative; FN = false negative
The table below lists the main statistical terms used in relation to screening tests:
Positive and negative predictive values are prevalence dependent. Likelihood ratios are not prevalence dependent.
Each one of the following statements regarding atrial natriuretic peptide are true, except:
Correct Answer D: Atrial natriuretic peptide: Basics:
Actions:
Which of the following physiological effects would be expected following administration of atropine?
Correct Answer E:
Atropine: Atropine is an antagonist of the muscarinic acetylcholine receptor.
Uses*:
Physiological effects:
*Atropine is no longer used in resuscitation.
You are a ST1 doctor working on a medical ward. You are struggling to cope with the workload and often leave the ward late.
Who is the most appropriate action to take?
Correct Answer D: Speaking to your consultant is the first action to take in this scenario. They are best placed to be able to take action to try and amend the situation. As the consultant is ultimately responsible for patient care they also have a right to know if you are struggling to cope as this may affect patient care.
The medical director may also be able to assist but would end up speaking to the consultant and hence is not the first choice.
Arriving early may seem an option but does not ultimately address the cause of the problem. Taking time off sick is the worst option - it doesn't address the problem and is unprofessional.
Which one of the following conditions is NOT an autosomal dominant condition?
Autosomal recessive conditions are 'metabolic' - exceptions: inherited ataxias.
Autosomal dominant conditions are 'structural' - exceptions: hyperlipidaemia type II, hypokalaemic periodic paralysis.
Autosomal dominant conditions:
Autosomal recessive conditions are often thought to be 'metabolic' as opposed to autosomal dominant conditions being 'structural', notable exceptions:
The following conditions are autosomal dominant:
*Type 3 von Willebrand's disease (most severe form) is inherited as an autosomal recessive trait. Around 80% of patients have type 1 disease.
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