Seminar 1 November 2005
Clinical notes:
44 year old male
Results:
| . |
. |
reference interval |
| TSH |
4.9 |
0.35-4.94 mU/L |
| Free T4 |
8.0 |
9.0-19.0 pmol/L |
Case 2
Clinical notes:
70 year old male with polyuria and polydipsia
Results:
| . |
. |
reference interval |
| sodium |
145 |
135-145 mmol/L |
| potassium |
4.3 |
3.5-5.0 mmol/L |
| chloride |
111 |
100-108 mmol/L |
| bicarbonate |
24 |
3.5-5.0 mmol/L |
| urea |
9.3 |
2.8-7.7 mmol/L |
| creatinine |
91 |
60-110 umol/L |
| calcium |
3.09 |
2.15-2.60 mmol/L |
| phosphate |
0.65 |
0.80-1.40 mmol/L |
| albumin |
38 |
35-50 g/L |
Case 3
Clinical notes:
38 year old female passing large volumes of urine.
Water Deprivation Test -- DDAVP given after 4 hour sample collected.
Results:
| . |
baseline |
1 hr |
2 hrs |
3 hrs |
4 hrs |
5 hrs |
6 hrs |
reference interval |
| se osm |
282 |
. |
297 |
. |
303. |
. |
. |
280-300 mmol/kg |
| ur osm |
73 |
83 |
84 |
95 |
101 |
82 |
85 |
40-1400 mmol/kg |
Questions
What is the diagnosis in each of these patients? (MAACB)
Each patient is on the same medication. What drug may be associated with these 3 conditions? (prize)
ANSWER AND FURTHER COMMENTS
Answers
1. Borderline hypothyroidism
2. Hypercalcaemia probably due to hyperparathroidism (high calcium, low phosphate, highish chloride, lowish bicarb).
3. Nephrogenic diabetes insipidus
Lithium
Further Comments
Effects of lithium on biochemical tests
John Cade in Melbourne introduced lithium (1949) as a treatment for mania. It is now used for treatment of mania, depression and schizophrenia. Some eminent academics, including Medical Biochemists owe their career to lithium. However lithium, even at therapeutic doses, may have an effect on the Endocrine system, possibly because it alters the conversion of ATP to cyclic AMP. Also what is considered a therapeutic dose now, is MUCH lower than in the past.
Thyroid Gland
Lithium is concentrated in the thyroid gland and affects several of the steps of thyroid gland synthesis and release. This may result in hypothyroidism (~10% of patients) so all patients should be screened before starting lithium and during treatment for hypothyroidism. It may occasionally be associated with hyperthyroidism usually in pre disposed individuals.
Hypercalcaemia
Lithium is associated with hypercalcaemia and hyperparathyroidism in about 10% of patients. Mechanism is unknown but it is probably resetting of the "set point" of the parathyroid response to calcium.
Water Balance
Lithium causes nephrogenic diabetes insipidus in about 20% of people. Lithium is excreted at the glomerulus and almost totally reabsorbed by the nephron, 50% occurring in the distal tubule. Distal tubular function may be affected resulting in concentrating problems and leading to nephrogenic diabetes insipidus. Kincaid -Smith is known for describing histological abnormalities in the distal tubules. These are reversed when lithium is discontinued but the diabetes insipidus may continue for weeks to months.
References
http://www.psychiatrictimes.com/p020156.html
http://www.clevelandclinicmeded.com/diseasemanagement/endocrinology/hcalcemia/hcalcemia.htm#lithium
http://www.emedicine.com/med/topic1313.htm
Water Deprivation Test
It is usual to give the patient a drink before gving DDAVP (ie at the end of the water deprivation part of the test) which is why the urine osmolality has fallen slightly.
You should know how to do the test and risks to the patient.