MSc in Clinical Biochemistry
West Midlands Training Course in Clinical Biochemistry & The University of Birmingham.
Short Answer Paper June 29th 2007
Answer all Questions
Time Allowed 1 hour 30 minutes
You will need to pass each module
Module 1
1. A 35 year old man has persistent hypertension and hypokalaemia. Following withdrawal of medication and correction of the hypokalaemia, plasma investigations were as follows:
0800h Recumbent 1200h Ambulent
Aldosterone 720 (Ref Range 100-450) 1270 (Ref Range 200 – 800)
pmol/L
Renin 0.1 (Ref Range 1.1-2.7) 0.3 (Ref Range 2.8 – 4.5)
nmol/L/hr
Cortisol 700 300
nmol/L
a. What is the likely diagnosis? 4 marks
b. What is the underlying cause? 4 marks
c. Explain why the serum cortisol is measured? 2 marks
2. A 10 year old boy was investigated for short stature and found to be hypocalcaemic. Further serum investigations showed:
Calcium (mmol/L) 1.81
Phosphate (mmol/L) 1.95
Alkaline Phosphatase(IU/L) 160 (Adult ref range 30-130)
Albumin (g/L) 40
Creatinine (umol/L) 60
Discuss these results and the likely differential diagnosis. 5 marks
Suggest further investigations required for clarification of the diagnosis and indicate what results you would expect for the two likeliest diagnoses. 5 marks
3. List 5 causes of hypophosphataemia. 2 marks each
4. 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 = 0.016 x Albumin + 1.698
a. Using the equation and the desired reference range of 2.10 – 2.60 mmol/L, calculate the adjustment equation for this laboratory, expressed in the form:
Adjusted calcium = calcium + A (B – albumin) 5 marks
What assumptions about the dataset do you need to make for the equation to be valid? 1 mark
b. The equation previously used by the laboratory was
Adjusted calcium = calcium + 0.025(40-albumin).
A patient had the results: Adjusted Ca 2.42 mmol/L, Albumin 25g/L. What would the new adjusted calcium result now be for the same patient? 4 marks
5. Parathyroid hormone has a plasma half life of 3 minutes. A patient undergoing a parathyroidectomy had an initial plasma value of 60 pmol/L. What was the level 20 minutes after isolation of the gland? 5 marks
How long until the PTH level was undetectable? (Limit of detection = 0.2pmol/L) 5 marks
Module 2
6. List 5 differences between type 1 and type 2 diabetes mellitus 2 marks each
7. A 70 year old man with back-pain was referred to a Haematologist because of a low haemoglobin of 10.2 g/dL (ref range 12.5-16.5) and a very high ESR of >100mm/hr (ref range <7). His serum biochemistry is detailed below:
Calcium (mmol/L) 3.16
Alkaline Phosphatase (IU/L) 110 (Ref Range 30-130)
Protein (g/L) 116
Albumin(g/L) 30
Creatinine (umol/L) 160
Parathyroid hormone (pmol/L) 0.2(Ref Range 0.5-5.5)
- a. Discuss the results and suggest the likely cause of the abnormalities shown. 6 marks
- b. What additional investigations should be undertaken to determine the diagnosis? 4 marks
8. The following plasma glucose results (mmol/L) were obtained on venous samples taken during a 75g oral glucose tolerance test. Interpret the results in the light of the WHO criteria.
Fasting 2 hour Symptoms
Case 1 6.0 7.7 None
Case 2 6.5 11.1 None
Case 3 6.3 7.5 None
Case 4 6.9 15.0 Polyuria/Polydipsia
Case 5 6.4 7.9 None
2 marks each
9. Calculate the LDL concentration in a male patient with the following serum lipid concentrations:
Total Cholesterol (mmol/L) 5.8
Triglycerides (mmol/L) 2.6
HDL Cholesterol (mmol/L) 1.3
8 marks
Briefly discuss the conditions under which LDL cholesterol calculations are invalid. 2 marks
10. A new screening test for diabetic nephropathy is positive in 97% of patients with the disease and 1% of patients without it. Calculate the probability that a patient with a positive test has the disease if the prevalence of the disease in those tested is
- a. 1 in 3 5 marks
- b. 1 in 100 5 marks
Module 3
- 11. The following results were obtained in a 50 year old diabetic with oedema after a 12 hour fast.
Serum Sodium (mmol/L) 138
Potassium (mmol/L) 3.6
Urea (mmol/L) 7.1
Creatinine (umol/L) 125
Albumin (g/L) 18
Glucose (mmol/L) 7.3
Cholesterol (mmol/L) 12
Triglycerides (mmol/L) 3.6
Urine Dipstick Protein +++
Glucose -ve
- a. What is the most likely diagnosis? 5 marks
- b. What test would help confirm the diagnosis? 3 marks
- c. Name the likely underlying cause 2 marks
- 12. A 40 yr old man with a long history of indigestion was admitted with a three day history of projectile vomiting. Investigations revealed
pH 7.52 (7.36-7.44)
pO2 7.9 kPa (9-13)
pCO2 8.5 kPa (4-6)
HCO3 42 (22-29)
a. What is the underlying acid-base disorder?
- b. Explain the PO2 and PCO2 results
- c. What would you expect the plasma potassium concentration to be?
- d. What are the expected urine pH and potassium levels?
- e. What is the likeliest cause for the underlying acid-base disorder?
2 marks each
- 13. Briefly describe the features of the refeeding syndrome
10 marks
14. A diabetic has a 24 hour urine output of 2L, a serum creatinine of 200 umol/L and a urine creatinine of 10mmol/L. Calculate the creatinine clearance.
10 marks
15. Calculate the pH of a solution formed by mixing 8mL of KH2PO4 (0.06M) and 12mL Na2HPO4 (0.06M). The pK for the H2PO4- H+ + HPO4 2- is 6.8.
10 marks
