Chem path 13 - Diabetes CPC Flashcards
What are the units for Hba1c and what is the cut off for diabetes?
mmol/mol, for a diagnosis of diabetes the Hba1c needs to be above 48mmol/mol (6.5%)
What is the normal value for Hba1c (non-diabetics)?
<42mmol/mol
WHat is the cut off for WHOLE fasted-blood in diabetics?
> /=6.1mmol/L
o 48yo unconscious, presented February 2002
o Acutely unwell a few days, vomiting, polyuria, polydipsia, SOB and dehydrated
o PMHx: appendicectomy, osteoporosis, poorly controlled HTN
o DHx: amlodipine 10mg, atenolol 100mg
o O/E: obese, dehydrated, BP 80/40
What is the cause of this woman’s unconsciousness and what investigation would you do next?
Hypotension
ABG
What are some causes of metabolic alkalosis?
H+ loss (i.e. vomiting)
Hypokalaemia (hypokalaemic alkalosis is a thing)
Ingestion of bicarbonate (i.e. lots of rennie in peptic uclers)
What will a high HCO3- do to CO2 levels?
It will slightly raise them due to a shift in the equilibrium and NOT as a form of compensation
What effect does metabolic alkalosis have on ventilation and why is the extent of respiratory compensation limited in metabolic alkalosis?
Metabolic alkalosis will inhibit ventilation so this will drive CO2 up further however the extent of compensation is limited because ventilation needs to remain sufficient to maintain good O2 levels so there is relatively little resp compensation for met alk.
How do you calculate osmolality?
2(Na+K) + U + G
How do you calculate the anion gap?
Na + K - Cl - HCO3-
How can the anion gap help you distinguish whether the cause is DKA or not?
DKA fuels a high anion gap through excess ketones
What is the link between hypokalaemia and alkalosis?
Hypokalaemia causes alkalosis and alkalosis causes hypokalaemia, need to figure out which came first
How does a low ECF K+ cause alkalosis?
Causes a drive of H+ in to cells (instead of K+)
How does an alkalosis cause hypokalaemia?
Causes a drive of K+ in to cells (instead of H+)
What are the 4 main causes of hypokalaemia?
GI loss, renal loss, redistribution in to cells and rare causes (GRRR)
Name some causes of renal losses of K+
Mineralocorticoid excess e.g. hyperaldosteronism/Conn’s, Cushing’s
Increased Na+ delivered to DCT
Osmotic diuresis
Name some causes of redistribution of potassium in to cells
Insulin/insulinomas
Beta agonists
Alkalosis
What are some rare causes of hypokalaemia?
Renal tubular acidosis types 1 and 2
Hypomagnesaemia - low magnesium means you will be unable to bring back up a low K+ so you have to correct the mg2+ before you can correct the K+
Explain the mechanism of renal potassium losses when excess Na+ reaches the DCT
Triple or co-transporter is blocked –> less Na+ is reabsorbed in the ascending LOH –> more reaches DCT.
More Na+ is absorbed in the DCT –> electronegative nephron which results in a loss of K+ down the electrochemical gradient through ROMK channels
Which drug class blocks the triple and co-transporter (Na+/Cl-), respectively?
Triple transporter: Loop diuretics
Co-transporter: Thiazides
Summarise the pathophysiology of hypokalaemia and alkalosis
Lack of extracellular K+ for exchange with Na+ –> Increased H+ entering cells and an extracellular alkalosis.
Lack of intracellular K+ –> increased excretion of H+ in exchange for sodium and the production of an acidic urine and generation of bicarbonate
Name 3 endogenous causes of CUshing’s syndrome
Pituitary adenoma
Adrenal tumour
Ectopic ACTH
What test is now done to assess for pituitary or ectopic cause of cushing’s instead of high dose dexamethasone suppression test?
IPSS (a high dose suppression test would have suppressed cortisol if pituitary cause but not ectopic, if adrenal cause then the ACTh would have been suppressed anyway)
How does ectopic ACTH cause hypokalaemia?
Such high doses of cortisol overpowers MR receptors which has an aldosterone-like effect and causes K+ loss
What are causes of ectopic ACTH?
Lung cancer (SCLC) Other cancers
