Chemical Pathology 12 - Meeran's Diabetes CPC (pituitary)

Question 1

What are the 3 biochemical definitions of diabetes?

Answer 1

Fasting PLASMA glucose >7.0mM (nb. this value does not apply to fingerprick whole blood test)

• normal plasma glucose : = 6
• impaired plasma glucose: 6. 1 - 6.9

HbA1c > 6.5% (equivalent >48mmol/mol)

2 hour plasma glucose in Glucose Tolerance Test of >11.1mM

impaired glucose tolerance test: 7.8-11.0

Question 2

What HbA1c values count as ‘impaired glucose tolerance’?

Answer 2

• < 42mmol/mol = NORMAL
• 42-47mmol/mol = PRE-DIABETES - impaired
• ≥ 48mmol/mol= DIABETES

Question 3

Recall 3 differentials for metabolic alkalosis

Answer 3

H+ loss via vomiting (see history)
Hypokalaemia
Bicarb ingestion (rennies)

NOTE: hypokalaemia and alkalosis should go together because as you LOSE K+, you swap this for HCO3^-

Question 4

What is the calculation for osmolality?

Answer 4

2(Na + K) + Urea + Glucose

Question 5

What is the calculation for anion gap?

Answer 5

Na + K - Cl - HCO3

Question 6

How can anion gap assist in diagnosis of DKA?

Answer 6

Ketones are anions
Therefore, in DKA anion gap will be large

Question 7

How can pituitary-dependent Cushing’s and ectopic ACTH be distinguished?

Answer 7

Pituitary petrosal sinus sampling

Question 8

If a patient has a high ACTH and very severe hypokalaemia, what is the most likely cause of the high ACTH?

Answer 8

Ectopic ACTH

• Ectopic ACTH causes hypokalaemia more often than other causes of Cushing’s

Question 9

What test is best to diagnose the cause of ectopic ACTH?

Answer 9

CXR + CT to look for lung cancer that produces ectopic ACTH

Question 10

How can acute and chronic renal failure be distinguished?

Answer 10

Renal biopsy

Question 11

How should acute tubular necrosis be managed?

Answer 11

Dialyse for 3 weeks and they willl recover

• ATN is VERY common in dehydrated patients
• If the patient is dehydrated, this is reversible

Question 12

How should diabetic glomerular kidney disease be managed?

Answer 12

This is a lifelong condition that will require lifelong dialysis

Question 13

What is the difference in expected pCO2 in uncompensated metabolic and respiratory acidosis?

Answer 13

Metabolic: low pCO2 (equilibrium pushed right to produce more CO2 but this is breathed off nicely)

Respiratory: high pCO2 (not ventilating properly to get rid of CO2)

Question 14

What is the difference in expected pCO2 in uncompensated metabolic and respiratory alkalosis?

Answer 14

Metabolic: high pCO2 (reduced H+ means resp rate decreases to produce more CO2 to replace H+)

Respiratory: low pCO2 (hyperventilation –> blowing off all CO2)

Question 15

How can hypoglycaemia lead to a respiratory alkalosis?

Answer 15

Can cause significant anxiety –> hyperventilation

Question 16

Why can very high serum omolality cause unconsciousness?

Answer 16

Brain gets VERY dehydrated

hypotensive due to the high osmolality

Question 17

What metabolic imbalance is caused by metformin?

Answer 17

Lactic acidosis

(These are anions so will cause high anion gap, but urine will be negative for ketones)

Question 18

good way to determine acid base status

Answer 18

Question 19

CASE 1: Mrs GB

• First presented in February 2002
• 48-year-old, unconscious
• Acutely unwell a few days
• Vomiting
• Polyuria and polydipsia
• Breathless
• Dehydrated

PMH:

• Appendicectomy
• Osteoporosis
• Poorly controlled hypertension

DH:

• Amlodipine 10mg
• Atenolol 100mg

Examination: obese, very dehydrated, BP: 80/40, Urine dipstick ++++ glycosuria

QUESTION 2: Differential Diagnosis? + what test should be done

Answer 19

• Hyperosmolar non-ketotic coma
• ABG

Question 20

Arterial Blood Gas

• pH: 7.65
• PCO2: 6.1kPa (N: 4.7-6.0
• PO2= 15kPa

QUESTION 4: What is the acid/ base abnormality?

Answer 20

Metabolic alkalosis

Question 21

Summary (Metabolic Alkalosis)

Answer 21

• High pH
• High HCO3
• High CO2
  
  • H⁺ + HCO3^‑ à CO2 + H2O

Respiratory compensation

Question 22

norma anion gap =

Answer 22

NORMAL suggests there are NO extra anions

Question 23

Causes of Longstanding Hypokalaemia?

Answer 23

• Taking mild thiazide diuretics can lead to longstanding HypoK