ChemPath

Question 1

Diagnosing impaired glucose tolerance

Answer 1

HbA1c 42-47mmol/L
or
Fasting plasma glucose 6.1-6.9mmol/L
or
OGTT (2hrs after 75g) 7.9-11.0mmol/L

Question 2

Anion gap

Answer 2

Na + K - Cl - bicarb

NB: ketones are unmeasured anions, therefore DKA will have a raised anion gap

Question 3

Osmolality

Answer 3

2(Na+K) + urea + glucose

Question 4

How to distinguish between DKA and HONKC?

Answer 4

Calculate osmolality (raised in HONKC) and anion gap (raised in DKA due to ketones)

Question 5

Management of hypoglycaemia

Answer 5

If alert - oral carbs
If drowsy but can swallow - sublingual glucose / hypostop
If unconscious, 100ml 20% glucose via large bore cannula
If persistent, 1mg IM / SC glucagon

Question 6

Causes of high anion gap

Answer 6

'KULT'
Ketones
Uraemia
Lactate
Toxins

Question 7

Causes of metabolic acidosis

Answer 7

Increased H+ production e.g. DKA, lactate
Decreased H+ excretion e.g. renal tubular acidosis
Bicarbonate loss e.g. fistulae

Question 8

Causes of metabolic alkalosis

Answer 8

H+ losses e.g. vomiting
Hypokalaemia (perpetuates alkalosis and vice versa)
Ingestion of bicarbonate

Question 9

Causes of respiratory acidosis

Answer 9

Hypoventilation
V/Q mismatch
Lung injury

Question 10

Causes of respiratory alkalosis

Answer 10

Hyperventilation e.g. mechanical or anxiety

Question 11

Low insulin + low c-peptide in the context of hypoglycaemia indicates what?

Answer 11

Appropriate response to hypoglycaemia e.g. malnutrition.

Question 12

High insulin and high c-peptide in the context of hypoglycaemia indicates what?

Answer 12

Inappropriate response to hypoglycaemia e.g. insulinoma or islet cell hyperplasia

Question 13

High insulin and low c-peptide in the context of hypoglycaemia indicates what?

Answer 13

Exogenous insulin administration

Question 14

Calcium normal range

Answer 14

2.2-2.6mmol/L but should not vary from one day to the next in each person

Question 15

3 forms of serum calcium

Answer 15

1. 50% biologically active free ionised calcium
2. 40% protein-bound (albumin)
3. 10% complex (citrate / phosphate)

Question 16

Symptoms of hypercalcaemia

Answer 16

Moans, bones, stones, groans, polyuria and polydypsia

Question 17

Causes of hypercalcaemia

Answer 17

Primary hypercalcaemia (PTH zero)

• hypercalcaemia of malignancy: paraneoplastic due to PTHrP from small cell lung Ca, due to bony mets, or due to cytokines stimulating osteoclasts in multiple myeloma.
• sarcoidosis
• vitamin D excess

Secondary hypercalcaemia (PTH not zero)

• primary hyperparathyroidism (commonest cause of hypercalcaemia) e.g. adenoma, or MEN1
• familial hypocalciuric hypercalcaemia (benign!)

Question 18

Management of hypercalcaemia

Answer 18

Medical emergency (Ca >3mmol/L)
Fluids
Treat underlying cause
Bisphosphonates if cause is cancer

Question 19

Symptoms of hypocalcaemia

Answer 19

Neuromuscular excitability - Chvostek`s and Trousseau`s signs
Hyperreflexia
Seizures
Stridor
Wide QT

Question 20

Causes of hypocalcaemia

Answer 20

Low PTH

• Iatrogenic (thyroidectomy)
• Autoimmune hypoPTH
• Congenital abscence (DiGeorge)
• HypoMg

High PTH (secondary hyperparathyroidism)

• vitamin D deficiency / osteomalacia
• CKD
• PTH resistance

Secondary hypocalcaemia

Question 21

Diagnosis of osteoporosis

Answer 21

T-score (mean of young healthy population) on DEXA scan:

Osteoporosis

Question 22

T score vs. Z score (DEXA)

Answer 22

T score = SD from mean of young healthy population (useful for fracture risk)
Z score = SD from mean of age-matched controls (useful to identify accelerated bone loss in younger pts)

Question 23

Diagnosing diabetes

Answer 23

HbA1c >/=48mmol/L (>/=6.5%)
or
Fasting plasma glucose >/=7mmol/L
or
OGTT (2hrs after 75g) >/=11.1mmol/L