Question 126#

Which one of the following may be used to calculate the number needed to treat?

A. 1 / (Absolute risk reduction)

Correct Answer A: 

NNT = 1 / Absolute Risk Reduction

Numbers needed to treat and absolute risk reduction:

• Numbers needed to treat (NNT) is a measure that indicates how many patients would require an intervention to reduce the expected number of outcomes by one
• It is calculated by 1/(Absolute risk reduction) and is rounded to the next highest whole number
• Experimental event rate (EER) = (Number who had particular outcome with the intervention) / (Total number who had the intervention)
• Control event rate (CER) = (Number who had particular outcome with the control/ (Total number who had the control)

Absolute risk reduction = CER-EER or EER-CER?

The absolute risk reduction (ARR) may be calculated by finding the absolute difference between the control event rate (CER) and the experimental event rate (EER). You will often find both versions of the above listed in different sources. In some ways in doesn't matter which you use as you will end up with the same answer but from a technical point of view:

• If the outcome of the study is undesirable then ARR = CER - EER
• If the outcome of the study is desirable then ARR* = EER - CER 

*this may be more accurately termed absolute benefit increase, rather than absolute risk reduction

 

Question 127#

What level of evidence does a randomized control trial offer? 

A. Ia

Correct Answer B: 

Study design: evidence and recommendations:
Levels of evidence:

• Ia - evidence from meta-analysis of randomized controlled trials
• Ib - evidence from at least one randomized controlled trial
• IIa - evidence from at least one well designed controlled trial which is not randomized
• IIb - evidence from at least one well designed experimental trial
• III - evidence from case, correlation and comparative studies
• IV - evidence from a panel of experts

Grading of recommendation:

• Grade A - based on evidence from at least one randomized controlled trial (i.e. Ia or Ib)
• Grade B - based on evidence from non-randomized controlled trials (i.e. IIa, IIb or III)
• Grade C - based on evidence from a panel of experts (i.e. IV)

Question 128#

A 67-year-old woman presents with lethargy, depression and constipation. A set of screening blood tests reveals the following:

• Calcium 3.05 mmol/l
• Albumin 41 g/l

What is the single most useful test for determining the cause of her hypercalcaemia?

A. ESR

Correct Answer D: Parathyroid hormone levels are useful as malignancy and primary hyperparathyroidism are the two most common causes of hypercalcaemia. A parathyroid hormone that is normal or raised suggests primary hyperparathyroidism.

Hypercalcaemia: causes:
The most common causes of hypercalcaemia are malignancy (bone metastases, myeloma, PTHrP from squamous cell lung cancer) and primary hyperparathyroidism.

Other causes include:

• Sarcoidosis*
• Vitamin D intoxication
• Acromegaly
• Thyrotoxicosis
• Milk-alkali syndrome
• Drugs: thiazides, calcium containing antacids
• Dehydration
• Addison's disease
• Paget's disease of the bone** 

*other causes of granulomas may lead to hypercalcaemia e.g. Tuberculosis and histoplasmosis.

**usually normal in this condition but hypercalcaemia may occur with prolonged immobilization.

Question 129#

Which one of the following is only secreted by the adrenal medulla?

A. Noradrenaline

Correct Answer E: Adrenal medulla:
The adrenal medulla secretes virtually all the adrenaline in the body as well as secreting small amounts of noradrenaline. It essentially represents an enlarged and specialized sympathetic ganglion. 

Question 130#

At which point in the menstrual cycle do progesterone levels peak?

A. Luteal phase

Correct Answer A: Progesterone is secreted by the corpus luteum following ovulation.

Menstrual cycle:

The menstrual cycle may be divided into the following phases:

Further details are given in the table below: