Course Assessment – Autumn 2006
Short Answer Questions. Answer all questions. Time allowed 1 hour.
- A laboratory wishes to check that its equation for adjusting calcium for albumin is correct for its current methods. A large dataset of paired calcium and albumin results is obtained from the laboratory computer, and a scatter plot of calcium (y-axis) versus albumin (x-axis) is graphed. The linear correlation is confirmed with an equation (in the form of y = mx+c):
Calcium = 0.012 x Albumin + 1.776
a) Using the equation and the desired reference range of 2.20 – 2.60 mmol/L, calculate the adjustment equation for this laboratory, expressed in the form:
Adjusted calcium = calcium + A (B – albumin)
What assumptions about the dataset do you need to make for the equation to be valid?
b) The equation previously used by the laboratory was
Adjusted calcium = calcium + 0.025(40-albumin).
A patient had the results: Adjusted Ca 2.99 mmol/L, Albumin 22g/L. What would the new adjusted calcium result now be for the same patient?
List the possible causes for the following results on a 45 year old woman in whom thyroid function tests were requested. There were no clinical details on the request form.
Free T4 2 pmol/L (10.0 – 24.0)
TSH 0.4 mU/L (0.50 – 4.50)
- Briefly describe 3 different analytical principles for estimating calcium and comment on the relative advantages /disadvantages.
- A radioisotope has a half life of 12 days. What percentage of the initial activity is remaining after 2 weeks and 7 weeks?
- A 40 year old man complains of intermittent acute confusional episodes on awakening and after exercise which rapidly resolve with oral carbohydrate. Four months previously he had a pituitary adenectomy for non-functioning benign pituitary adenoma. Initial investigations reveal hypercalcaemia (serum corrected calcium = 2.70 mmol/L) Further investigations are listed below
Synacthen test
Time (minutes) 0 30 60
Cortisol(nmol/L) 400 650 700
Prolactin, thyroxine, TSH, testosterone, LH, FSH, GH and IGF1 are all normal.
What is the likely diagnosis and list the further investigations?
The absorbance of a coloured solution is 1.2 in a 1cm cell at a concentration of 0.002M. For a more accurate measurement an absorbance of 0.35 is required. If the molecular weight of the coloured compound is 560, what weight of the compound should be used to prepare 10mL of the solution.
- How would you prepare a 1 mol/l buffer pH 5.2 from sodium acetate and acetic acid (pka 4.74)
- Calculate the approximate osmolality of an iv solution of dextrose saline containing 3% w/v glucose and 0.45% w/v sodium chloride.
- Describe briefly the stepwise investigation of a patient suspected of having Cushings syndrome/disease.
10. A patient with severe water depletion has excreted only 100 mL of urine in the last 6 hours. A short time before this the patient was found to have a creatinine clearance of 100 mL/min and a plasma creatinine of 100 umol/L. Assuming the same clearance during the water depletion what would be the creatinine concentration in the latest 100 mL urine?
