MSc in Clinical Biochemistry
West Midlands Training Course in Clinical Biochemistry & The University of Birmingham.
Short Answer Paper July 2004
Answer all questions.
Clinical Cases: -
- A 68 yr old woman on lithium, carbamezepine and lactulose has a 24 hour urine volume of 4.5litres. The results of a fluid deprivation test were: -
Time Urine Vol Urine Osm Serum Na Serum Osm
10.00h 150 180 149 312
11.00h 200 177 150 317
12.00h 150 175 151 314
12.30 2ugs Desmopressin given IM
13.00h 175 179 - 311
14.00h 100 197 - 303
15.00h 180 182 - 297
16.00h 90 194 - 301
Basal: Creatinine 138 umol/L (60 – 120)
Questions
- What abnormalities are apparent and what is the likely diagnosis?
- What is the most likely underlying cause in this particular case?
- What other endocrine abnormalities may sometimes be associated with the underlying cause?
- A 42 year old Caucasian man returns from a Mediterranean holiday and presents to the accident and emergency department giving a history of weakness, vomiting, and of dizziness on standing. The Casualty Officer notices that the patient has a good sun tan but some unusual pigmentation also.
The following biochemistry was found: -
Sodium 118 mmol/L
Potassium 5.9 mmol/L
Urea 9.8 mmol/L
Creatinine 125 mmol/L
Questions: -
- Briefly highlight the abnormalities these results and suggest a possible endocrine cause for the presentation.
- What would be the most appropriate endocrine investigation to undertake at this time.
- Briefly describe how the test should be performed and what precautions should be taken.
3. A 60 year old woman complaining of lethargy and weight gain presented to her general practitioner. She has a family history of coronary artery heart disease and hypertension .
Total Cholesterol 10.0 mmol/L
HDL Cholesterol 1.8 mmol/L
Triglycerides 0.8 mmol/L
Creatinine Kinase 1534 IU/L (10-180)
Creatinine 145 umol/L (60 –120)
- The trainee GP contacts the laboratory for an interpretation of these data and suggestions for further immediate biochemical investigations. What would be your response?
4. The following serum capillary zone electrophoresis (CZE) trace was obtained on a sample from 59 year old man complaining of low back pain and fatigue. : -
Additional test results: -
Total Protein 77 g/L (Ref Interval 60 – 85)
Albumin 42 g/L (Ref Interval 35 – 48)
ESR 26 mm/Hr (Ref Interval 0 –14)
- Give a brief interpretation of the trace
- What is the most likely diagnosis?
- List further investigations that should be carried out on this sample.
- Using WHO criteria classify the following 75g oral glucose tolerance tests. Add any additional comments that you think should be appended to a report form. The values are for venous plasma glucose measurement: -
- A 55 year old lady complaining of polyuria and polydipsia
| Time (Minutes) | Plasma Glucose mmol/L |
| 0 | 7.2 |
| 120 | 14.3 |
- A 55 year old man attending a well man clinic who had a fasting blood glucose of 6.2 other without symptoms.
| Time Minutes | Plasma Glucose mmol/L |
| 0 | 5.9 |
| 120 | 7.7 |
c) An obese 58 year old man with hypertension and a fasting plasma glucose of 6.4 mmol/L.
| Time Minutes | Plasma Glucose mmol/L |
| 0 | 6.5 |
| 120 | 8.3 |
d) A 48 year old woman with weight loss, polyuria and polydipsia. Random plasma glucose 12.5 mmol/L and fasting plasma glucose 11.2 mmol/L.
| Time Minutes | Plasma Glucose mmol/L |
| 0 | 9.0 |
| 120 | 18.0 |
- The following results were obtained on assay of samples taken using a vacutainer system, from a 42 year old women attending a pre-operative assessment clinic. The patient was due to undertake elective cosmetic surgery other wise well and not receiving any other medical treatment. The request form indicated that the patient had been difficult to bleed.
Sodium 140 mmol/L (133 – 147)
Potassium 7.6 mmol/L (3.5 – 5.0)
Urea 3.8 mmol/L (2.5 – 7.5)
Creatinine 90 µmol/L (50-110)
Calcium 0.9 mmol/L (2.05 – 2.60)
Albumin 40 g/L (35 – 48)
Corrected Calcium 0.9 mmol/L (2.05 – 2.60)
Full Blood Count. All parameters within reference limits
Briefly indicate the possible cause of the abnormalities observed.
List, with reasons for their choice, any further tests that you may undertake on this sample to confirm your suspicions as to the cause.
- An 18 year old man with anorexia nervosa was admitted, having collapsed after alcohol ingestion. He weighed 29kg. Plasma glucose concentration was <1 mmol/L and serum phosphate concentration 1.34 mmol/L. He responded to intravenous dextrose. After 2 days the plasma phosphate concentration fell to 0.45 mmol/L and after 4 days to 0.2 mmol/L. Explain the reasons for this fall in phosphate.
- A 22 year old patient presents with pitting oedema and the following biochemical results.
Total Protein 39 g/L
Albumin 22 g/L
Cholesterol 17.5 mmol/L
Triglycerides 2.8 mmol/L
Briefly comment on these data. What are the most likely differential diagnoses? Suggest one further preliminary biochemical test to indicate a probable cause of the abnormalities seen.
- An 80 year old man with chronic obstructive airways disease and taking diuretics for associated cardiac failure presented with the following biochemistry results:-
Plasma potassium 2.6 mmol/L (3.2-4.8)
Blood pH 7.41 (7.35-7.45)
PCO2 10.3 kPa (4.6 – 6.0)
HCO3 48 mmol/L (24-32)
Briefly comment on these results and indicate the type or types of acid base disturbance present.
- A 36 year old married women complained of amenorrhoea for 2 months and has had several pregnancy test over the preceding month. The GP asks for a prolactin measurement which is reported as 1240 mU/L.
The GP contacts you to ask for an interpretation of this result? Briefly indicate the questions that you would immediately ask him and indicate which further investigations you would wish to undertake on this specimen to help with your interpretation.
Calculations
- A patient is found to have a serum digoxin concentration of 3.9 µg/L. Digoxin administration was stopped and a further sample taken for analysis 97 hours later. If the half life of digoxin in the circulation is 38 hours what would be the predicted concentration of digoxin in this serum sample.
- An immunoassay for peptide-X involved extraction of 1mL of serum with 5mL of methanol. The methanol was evaporated to dryness under nitrogen and the residue re-dissolved in 250 µL of assay buffer. Aliquots (100 µL) of this solution were assayed in duplicate in an immunoassay calibrated, against non-extracted standards, to give a result in terms of femtomoles (fmol) per assay tube. If the mean result of the duplicate assay of re-dissolved extract gave a result of 8 fmol/tube, and the average expected recovery for peptide-X extraction is 80%, calculate the concentration of peptide-X in the original sample in terms of picomoles per litre.
- Calculate the number of mmols of sodium reabsorbed in 24 hours by the kidneys of a healthy 70 Kg man. Assume a daily urinary sodium excretion of 100 mmols. Clearly state the assumptions you make
14. A screening test for a disease has a diagnostic sensitivity of 95% and a diagnostic specificity of 98%. Calculate the negative predictive value of the test, and the efficiency of the test, given that testing of a randomly selected sample of 100,000 subjects revealed 100 false negative test results.
