Clinical chemistry cases

Question 1

effect of hyperventilation on Ca levels

Answer 1

pH up - blow off CO2 = alkalotic
Ca stick more to protein = ionised ca fall further
= hypoca = paralysis/tetany

Question 2

Effect of low K

Answer 2

VF

Question 3

Effect of high K

Answer 3

Asystole

Question 4

Difference between colles’ and smith’s fracture

Answer 4

Colles - extended wrist
Smith’s - flexed wrist

Question 5

What is a Potts fracture

Answer 5

ankle fracture involving tibia and fibula

Question 6

ddx for high ca

Answer 6

- Primary hyperparthyroidism - commonest cause in community

- Sarcoid

- Cancer **- commonest cause in hospital (hyperca of malignancy is a really bad diagnosis - because it means the malignancy is invading bones - only have a 6mo Px)

Question 7

Ix for high Ca

Answer 7

PTH

Question 8

Interpreting PTH with high Ca

Answer 8

High ca and normal PTH - primary hyperparathyroidism

*Reference range for normal PTH is in healthy people. If ca is high - PTH should be suppressed - so the fact that it is normal means it is primary hyperparathyroidism *

High Ca and low PTH - cancer

Question 9

Mechanism of primary hyperparathyroidism -> high ca

Answer 9

Uncontrolled release of PTH
* Turn on osteoclasts - release ca from bone
* Activate vit D - 1a Vit - retain ca from urine *(ie less loss in urine) *
* Enhanced ca absorption from intestines
*

Question 10

Summarise Vit D metabolism

Answer 10

We measure 25-OH-vit D (the store)
It is activated under control of PTH in kidney

Question 11

Metabolic profile in hyperparathyroidism

Answer 11

PTH - H/N
Ca - H
Phos - L
Vit D - N
Alk phos - H (as osteoblasts try to rebuild bone)

Question 12

sx of hypercalcaemia

Answer 12

moans, bones, groans, stones
* psychic groans = depression
* abdo moans = pancreatitis/kidneu stones
asx
polydipsia
bones - brown tumours

Question 13

signs of hypercalcaemia

Answer 13

band keratopathy

Question 14

Complications of hypercalcaemia

Answer 14

• Renal stones
• Pancreatitis
• Peptic ulcer disease
• Skeletal changes
• Oestitis fibrosa et cystica (really long standing high ca) - little holes in skull as osteoclast try to release ca.

Question 15

RF for kidney stones

Answer 15

FH
Dehydration
High ca
Hypercalciuria >6mmol/day
HPTH

Question 16

Presentation of renal stones

Answer 16

• Colic
  
  • Haematuria
  • Recyrrent infection
  • Renal failyre

Question 17

Ix for renal stones

Answer 17

• KUB
  
  • Stone analysis
    Urine and serum biochem

Question 18

Mx of renal stones

Answer 18

Natural hx - Most stones past
Mx
- Lithotrypsy - balast with USS make it into gravel
- Cystoscopy
- Lithiotomy - remove surgically

Question 19

Prevention of renal stones

Answer 19

• Drink more
  
  • Treat hypercalciuria - thiazide diuretics to reduce ca in urine - stop painful colic, haematuria and recurrent infections
  • Treat hypercalcaemia

Question 20

Emergency mx of hypercalcaemia

Answer 20

Massive amounts of fluid - keep giving saline, takes a few days to work

Question 21

Emergency mx of hypercalcaemia

Answer 21

**Massive amounts of fluid - keep giving saline, takes a few days to work
**
Hold of pamidronate!!:
If give pamidronate - then bones are locked with bisphosphoate - so if take out the parathyroid gland - would be hypoca for a month.
Don’t use bisphosphonates if have primary hyperparathyroidism

Question 22

Non-emergency mx of hypercalcaemia

Answer 22

keep well hydrated
avoid thiazides
surgery

Question 23

Surgery for primary hyperparathyroidism

Answer 23

Minimally invasive parathyroidectomy
Techneium scan - small black dot. And USS

Patient immediately cured - ca returns to normal

Lots of cells all growing together - capsulated only way you know benign.
Parathyroid cancer is very rare

Question 24

What bone findings will you see in long standing hyperparathyroidism

Answer 24

most will have a normal XR, radial aspect of bones

more affected = cystic changes

Histology - will see brown tumours - hyperplastic osteoclasts

Question 25

Summarise Looser zone

Answer 25

*profound vit D deficiency. *

Area of decalcification caused by vit D deficency

Question 26

what does this show

Answer 26

Bilateral hilar lymphadenopathy

Question 27

what is seen in this histology - sarcoid

Answer 27

multinuclear giant cells when biopsy - smooth non-caseating granulomas

Question 28

Chem path in sarcoid

Answer 28

**High Ca
low PTH - undetectable
**

Sarcoidosis -> high ca because macrophages in lymph noides release 1a hydroxylase and not regulated by PTH.
Get seasonal hyperca - because it just compensates for the vit D deficiency

Question 29

Rx of sarcoid

Answer 29

Steroids - they will normalise the ca and treat the lung problem
○ Need to do slowly - otherwise get all issues of steroids
○ Only give if breathless etc. Have high dose 40 for a week - then low dose - but ideally take off because SE of steroids

If not ill - then just reassure and observe because steroids have SE

Question 30

How does cancer cause hyper calcaemia

Answer 30

• Cancer cells** invade bone- cause Ca to be released**
  
  • Some cancer cells **release PTHrp **- causes hyperca - and allows cancer cell to invade bone because pretends to be PTH, bone will make way for it by activating osteoclast.
    If you know cancer **- use bisphosphonate **- osteoblast make bone with bisphosphonate and cancer cannot invade because bisphosphonate is resistant to osteoclasts