Biology of Disease

CASE STUDIES

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CASE STUDY 7.1

Sarah, a 46-year-old woman, was referred to hospital

because of her excessive thirst and frequent urination

over the preceding two months. Her thirst was severe and

she had to drink water every few hours. An analysis of her

plasma and urine yielded the following results (reference

ranges are given in parentheses):

Plasma: Na+ 139 (136–146 mmol dm–3)

K+ 4.2 (3.7–5.1 mmol dm–3)

Creatinine 105 (65–121Mmol dm–3)

Osmolality 296 (282–296 mmol kg–1)

Urine: Glucose negative

Osmolality 90 (up to 1400 mmol/kg)

A fluid deprivation test was performed and the following

results were obtained for the plasma and urine osmolality:

Plasma: Osmolality 310 (282–296 mmol kg–1)

Urine: Osmolality 225 (up to 1400 mmol kg–1)

She was allowed to drink water on completion of the test

and given a dose of desmopressin after which her urine

osmolality increased to 620 mmol kg–1.

Questions

(a) What could be the causes of Sarah’s symptoms?

(b) Account for the plasma and urine data.

(c) Discuss the need for and results of the fluid

deprivation test.

CASE STUDY 7.2

Ian, a 53-year-old man went to see his family doctor

complaining of weakness. Thyroid function tests were

requested to exclude the possibility of hypothyroidism.

These tests showed the following results (reference ranges

are given in parentheses):

TSH 7.5 mU dm–3 (0.2–4.0 mU dm–3 )

Free T 4 14.5 pmol dm–3 (12–25 pmol dm–3)

Questions

(a) What is the most appropriate clinical explanation of

these results?

(b) What other signs and symptoms should be looked

for?

(c) How should Ian’s progress be monitored?

CASE STUDY 7.3

Amelia, a 20-year-old student, had not been feeling well

for three weeks. She was admitted to her local hospital

with a history of weakness and vomiting over the previous

three days. On admission she was unconscious. Clinical

tests on serum yielded the following data (reference

ranges are given in parentheses):

Na+ 113 mmol dm–3 (137–144 mmol dm–3)

K+ 5.8 mmol dm–3 (3.3–4.2 mmol dm–3)

Urea 30 mmol dm–3 (2.6–6.5 mmol dm–3)

pH 7.3 (7.35–7.45)

Questions

(a) What is the most likely explanation of these

results?

(b) What is the probable cause of Amelia’s condition?

(c) Having identified her condition, how should Amelia

be treated?