Chemical Pathology 12 - Meeran's Diabetes CPC (pituitary) Flashcards
What are the 3 biochemical definitions of diabetes?
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
What HbA1c values count as ‘impaired glucose tolerance’?
- < 42mmol/mol = NORMAL
- 42-47mmol/mol = PRE-DIABETES - impaired
- ≥ 48mmol/mol= DIABETES
Recall 3 differentials for metabolic alkalosis
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-
What is the calculation for osmolality?
2(Na + K) + Urea + Glucose
What is the calculation for anion gap?
Na + K - Cl - HCO3
How can anion gap assist in diagnosis of DKA?
Ketones are anions
Therefore, in DKA anion gap will be large
How can pituitary-dependent Cushing’s and ectopic ACTH be distinguished?
Pituitary petrosal sinus sampling
If a patient has a high ACTH and very severe hypokalaemia, what is the most likely cause of the high ACTH?
Ectopic ACTH
- Ectopic ACTH causes hypokalaemia more often than other causes of Cushing’s
What test is best to diagnose the cause of ectopic ACTH?
CXR + CT to look for lung cancer that produces ectopic ACTH
How can acute and chronic renal failure be distinguished?
Renal biopsy
How should acute tubular necrosis be managed?
Dialyse for 3 weeks and they willl recover
- ATN is VERY common in dehydrated patients
- If the patient is dehydrated, this is reversible
How should diabetic glomerular kidney disease be managed?
This is a lifelong condition that will require lifelong dialysis
What is the difference in expected pCO2 in uncompensated metabolic and respiratory acidosis?
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)
What is the difference in expected pCO2 in uncompensated metabolic and respiratory alkalosis?
Metabolic: high pCO2 (reduced H+ means resp rate decreases to produce more CO2 to replace H+)
Respiratory: low pCO2 (hyperventilation –> blowing off all CO2)
How can hypoglycaemia lead to a respiratory alkalosis?
Can cause significant anxiety –> hyperventilation
Why can very high serum omolality cause unconsciousness?
Brain gets VERY dehydrated
hypotensive due to the high osmolality
What metabolic imbalance is caused by metformin?
Lactic acidosis
(These are anions so will cause high anion gap, but urine will be negative for ketones)
good way to determine acid base status
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
- Hyperosmolar non-ketotic coma
- ABG
Arterial Blood Gas
- pH: 7.65
- PCO2: 6.1kPa (N: 4.7-6.0
- PO2= 15kPa
QUESTION 4: What is the acid/ base abnormality?
Metabolic alkalosis
Summary (Metabolic Alkalosis)
- High pH
- High HCO3
- High CO2
- H+ + HCO3‑ à CO2 + H2O
Respiratory compensation
norma anion gap =
NORMAL suggests there are NO extra anions
Causes of Longstanding Hypokalaemia?
- Taking mild thiazide diuretics can lead to longstanding HypoK
