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Explain how measurements of both total and direct bilirubin can contribute to a differential diagnosis.

Blood Sciences

Case-based discussion 2021-22

An 84-year-old woman, patient B, visited her GP as she was experiencing intermittent bouts of feelings of nausea.  She described her situation as having “good days and bad days” and the problem was particularly apparent just after she had eaten.  The symptoms were not accompanied by vomiting and she did not report any incidents of diarrhoea.  When questioned on her life recently there had been nothing unusual of note and she had not recently travelled overseas.  She did however report easily feeling tired but had put it down to her age.  The doctor took some blood samples to enable further investigation and some of the results from the tests are shown in the tables below.

Table 1a: results from the Haematological analysis of blood taken from patient B

Prothrombin time (PT) (sec)

15

White Blood Cell Count (109/l)

6.2

Red Blood Cell Count (1012/l)

3.3

Haemoglobin (g/l)

75

Haematocrit (l/l)

0.24

Mean Cell Volume (fl)

72

Mean Cell Haemoglobin (pg)

23

Mean Cell Haemoglobin Concentration (g/l)

312

Red Cell Distribution Width (%)

16.8%

Platelets (109/l)

480

 

Table 1b: results from the Biochemical analysis of blood taken from patient B

Parameter

Value

Total protein (g/L)

65

Albumin (g/L)

29

Total bilirubin (µmol/L)

48

Direct bilirubin (µmol/L)

41

Aspartate transaminase (AST) (U/L)

49

Alanine transaminase (ALT) (U/L)

39

Alkaline phosphatase (ALP) (U/L)

231

Gamma glutamyl transferase (γGT) (U/L)

52

Question 1

For each parameter in Table 1b except bilirubin, briefly explain the underlying biochemistry and how it links to the parameter being used to contribute to a clinical diagnosis in the context of the patient.  Your answer should not exceed 400 words.                 (25 marks)

Question 2

Explain how measurements of both total and direct bilirubin can contribute to a differential diagnosis.                                                                                                                        (10 marks)

Question 3

Table 2 shows the quality control data for the assays run to determine values for some of the parameters in Table 1b.  With reference to the expected values given for the QC for each parameter, and showing your workings, determine whether each assay is valid.  
                                                                                                                                    (15 marks)

Table 2: quality control values

 

 

Parameter

Measured

Expected

Total protein (g/L)

42.6

45.5

Albumin (g/L)

23.1

27.0

Total bilirubin (µmol/L)

95.2

91.5

Direct bilirubin (µmol/L)

32.8

31.2

Aspartate transaminase (AST) (U/L)

138

150

Alanine transaminase (ALT) (U/L)

83

80

Alkaline phosphatase (ALP) (U/L)

122

120

Gamma glutamyl transferase (γGT) (U/L)

116

135

 

Question 4

Considering the data for patient B, and referring to the reference ranges for the parameters shown in Table 3, identify which parameters are normal and which are a cause for concern.                                                                                                                               (10 marks)

Table 3: reference ranges

Parameter

Value

Total protein (g/L)

60-80

Albumin (g/L)

35-50

Total bilirubin (µmol/L)

2-20

Direct bilirubin (µmol/L)

<7

Aspartate transaminase (AST) (U/L)

10-50

Alanine transaminase (ALT) (U/L)

5-42

Alkaline phosphatase (ALP) (U/L)

30-150

Gamma glutamyl transferase (γGT) (U/L)

5-55

Prothrombin time (PT) (sec)

13-16

White Blood Cell Count (109/l)

4.0-11.0

Red Blood Cell Count (1012/l)

    Female: 3.8-5.8

Haemoglobin (g/l)

Female: 115-165

Haematocrit (l/l)

Female: 0.37-0.47

Mean Cell Volume (fl)

76-100

Mean Cell Haemoglobin (pg)

27-32

Mean Cell Haemoglobin Concentration (g/l)

310-350

Red Cell Distribution Width (%)

10-14.5

Platelets (109/l)

150-400

Question 5

Suggest two possibilities for a diagnosis for the patient, giving the reasons behind your suggestions.  Also briefly suggest what further investigations are likely to be carried out by the clinicians.                                                                                                                    (15 marks)

Question 6

Looking at the data for the haematology, identify any abnormalities and suggest the reason in the context of the patient.           Explain why the full blood count parameters are altered in the condition indicated.                                                                                                        (15 marks)

Question 7

For the two dye-binding assays in the practical, a reagent blank was used for the determination of albumin by Bromocresol Green.  However sample blanks were used for the measurement of bilirubin by the Jendrassik-Grof method.  In the context of the practical explain the difference between the two types of blanks and why they are used.            

(10 marks)

This piece of coursework should not exceed 1200 words excluding all questions and all details of calculations. For question 1 we have specified that the word count should not exceed 400 words, this is to ensure that your answer is clear and succinct. Please make sure that you keep to all word limits specified as you will be penalised for any submission exceeding the word count.


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