MSc in Clinical Biochemistry

West Midlands Training Course in Clinical Biochemistry & The University of Birmingham. 

Short Answer Paper June 29^th 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

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