Biochemical tests Flashcards
what are the plasma components usually measured?
– Sodium
– Potassium
– Chloride
– Bicarbonate
– Urea
– Creatinine
why is water so important?
fundamental to all blood test as patients hydration is important
where is sodium present?
it is an extracellular cation- outside
what is the main function of sodium
maintain osmolality
what are the major route of sodium excretion?
kidneys
what hormones help the kidneys excrete/ maintain sodium balance?
– Antidiuretic hormone
– Aldosterone
– Thirst
what are changes in serum sodium concentration usually due to?
– Diet (rich or low in sodium)
– The amount of water in the blood
– Kidney function
define hypernatraemia
Defined as a plasma sodium concentration of:
– > 145 mmol/L
what causes hypernatraemia?
– Water depletion
* Loss of water in excess of sodium
* Decreased fluid intake
– Increased sodium intake or retention in excess of
water
* Mineralocorticoid excess
* Medication
* Renal failure
what are some of the signs and symptoms of hypernatraemia?
– Dry skin
– Postural hypotension
– Oliguria
– Thirst
– Confusion
– Drowsiness, lethargy
– Extreme cases – coma (>155 mmol/L)
what are the drugs associated with an increased sodium- hypernatraemia?
– Corticosteroids
– NSAIDs
– Laxatives
– Lithium
why must you consider the make up of injectable drugs and soluble preps?
as sodium content could be high
how do you manage hypernatraemia?
- Identify and treat underlying cause
- Replace body water
– Orally
– Intravenously - Dextrose 5% w/v
define hyponatraemia
Low sodium is defined as a serum sodium
concentration below 135mmol/L
generally what does low sodium indicate?
– Over hydration in the body
– Too little sodium in the body
– Or a mixture of both
what may result from hyponatraemia?
May also include cardiac failure, anorexia and oedema.
what are the potential causes of hyponatraemia?
– Medication
– Mineralocorticoid deficiency
– Water/fluid excess
* SIADH
* Certain disease states
– Abnormal losses of sodium
* Diarrhoea, DKA
– Alcohol excess
– Severe burns
– Malnutrition
– Dilution of blood sample by IV fluids
how do you manage hyponatraemia?
– Identify and correct the underlying cause
– Depending on cause:
* Increased salt intake
* Fluid restriction
– If needed:
* Mild – moderate:
– Slow – sodium, 4 – 8 tablets (2.4 – 4.8g)
– Demeclocycline 900 – 1200mg daily in divided doses
* Severe:
– I/V NaCl
why do you not increase levels of sodium quick?
Remember, do not increase levels too
quickly due to the risk of osmotic
demyelination
where is potassium located in the body?
in the cell- intracellular cation
how is k+ regulated?
- Regulated by aldosterone, cortisol, insulin and
glucose
what do changes in k+ have an effect on?
- Changes in potassium levels have a profound
effect on the nervous and cardiovascular system - → fatal in extreme cases
where is k+ absorbed/ eliminated?
– Mainly absorbed in the small intestine
– Eliminated via the kidneys
where is k+ in peoples cells when they are hydrated/dehydrated?
– Potassium is lost from cells when people are
dehydrated and returns when hydrated
how are k+ levels influenced?
– Acid-base disturbances
* Acidosis (K moves out of cells in exchange for H)
* Alkalosis (K moves into cells in exchange for H)
– Catabolic states
– Anabolic states
– Insulin secretion
where is the main route of k+ loss?
via kidneys- small amoung in faeces and skin
what are some of the causes of hyperkalaemia?
- Medication
- Renal
- AKI
- CKD
- Rhabdomyolysis
- Hypoaldosteronism
- Advanced CCF
- Acidosis
- DKA
how do you exclude pseudohyperkalaemia from hyperkalaemia
Delay in sample reaching the lab
* Contamination
* Haemolysis of sample
* Drip arm
what are signs and symptoms of hyperkalaemia?
- Fatigue
- Muscle weakness
- Abnormal cardiac conduction
- Chest pain and palpitations
- ECG changes
- Cardiac arrest (severe cases)
how do you manage hyperkalaemia?
– Assess patient: ABCDE
– Identify cause/stop potentially offending drugs
immediately
– Rule out a pseudohyperkalaemia
– Ensure adequate hydration
– Consider the severity
* Severe/ECG changes: MEDICAL EMERGENCY
when do you refer someone with hyperkalaemia to hospital?
– >6.5mmol/L
– Acute ECG changes and >5.5 mmol/L
– Rapid rise
what do you do if there is mild hyperkalaemia?
– Correct underlying cause, repeat blood test
– Medication review and dietary changes are often adequate
what do you do for moderate hyperkalaemia?
– Carry out an ECG
* Assess course of action based on this
* No high-risk factors, review patient
what is the 5 step hospital approach for the management of hyperkalaemia?
- Step 1: Protect the heart
- Step 2: Shift potassium into cells
- Step 3: Remove potassium from the body
- Step 4: Monitoring
- Step 5: Prevention
how do you protect the heart in hyperkalaemia?
- If there are ECG changes
– 30ml of 10% calcium gluconate IV OR
– 10ml of 10% calcium chloride IV
how do you shift potassium into cells?
- Insulin-glucose infusion
– 10 units of soluble insulin in 250ml dextrose 10% - 10 – 20mg salbutamol nebuliser
– IHD - Shifts into the cells temporarily, this is a holding measure
only
– Does not reduce total body potassium - Will start to leak back into extracellular space (2 –
6 hours)
how do you remove potassium?
- Potassium exchange polymers
- Anion exchange resin
– Calcium resonium: 15g TDS - Potassium binders
– Patiromer calcium
– Lokelma (sodium zirconium cyclosilicate)
dialysis
when do you have to do continuous monitoring with hyperkalemia patients?
where ECG features are present
k+ every 2-4 hours
* Blood glucose levels
* Baseline, 15, 30, 60, 90, 120 minutes and
up to 6 hours post dose
how do you prevent hyperkalemia recurring?
Stop nephrotoxic medications and drugs
known to contribute to hyperkalaemia.
what are the causes of hypokalaemia?
- Medication
- Decreased intake
- Abnormal losses
- D&V
- Ileostomy
- Acid-base
disturbances
what are the signs and symptoms of hypokalaemia?
- Hypotonia
- Cardiac arrhythmias
- Muscle weakness
- Fatigue
- Confusion
- Paralytic ileus
what are some of the drugs causing hypokalaemia?
Salbutamol (especially in high doses)
Thiazide diuretics
Loop diuretics
Insulin
Steroids
Chronic laxative abuse
how do you manage hypokalaemia?
– Depend on the severity
– Correct underlying cause or disease process
– Use potassium sparing drugs
– Oral treatment
– Intravenous treatment
how do you manage mild and moderate hypokalaemia?
– Oral replacement
* Sando K®: 1 – 2 tablets TDS
* Kay-Cee-L: 10ml – 20ml TDS
* Slow K: avoid where possible
how do you manage severe hypokalemia?
– IV replacement (with continuous cardiac monitoring – depending on
potassium concentration)
– Doses vary across guidelines
– Doses and rates may vary in critical care or fluid restricted patients
where is there increased risk of digoxin toxicity and why?
– There is an INCREASED risk of digoxin
toxicity in the presence of hypokalaemia
– Digoxin competes with potassium ions at
binding sites, therefore, a low potassium
predisposes to toxicity.
what is the usual range for chloride?
Usual range is 95 – 105mmol/L
what does chloride usually follow?
- Movement follows that of sodium
what causes and increase in CL-?
excess ingestion
dehydration
what causes a decrease in cl?
vomiting
diarrhoea
diuresis
dehydration
what does bicarbonate reflect?
- Reflects renal, metabolic and respiratory functions
what would be the signs and symptoms of inc/dec bicarbonate?
inc- vomiting
dec- headache, drowsiness, coma
what are the causes of increased bicarbonate?
excess antacids
thiazide and loop diuretcis
metabolic alkalosis
hypokalaemia
vomiting
what are the causes of decreased bicarbonate?
diarrhoea
renal failure
diabetes
metabolic acidosis
respiratory alkalosis
what is the end product of protein metabolism?
urea
what causes raised urea?
renal failure
sepsis
uti
CCF
dehydrayion
GI bleed
what causes decreased urea?
pregnancy
low protein
cld
over hydration
starvation
what is the end product of metabolism
creatine
what is the end product of metabolism
creatine
what happens if kidney filtration is impaired?
serum creatine will rise
what are reduced levels of calcium associated with?
– Renal failure
– Raised phosphate levels (as phosphate binds to
calcium readily)
– Hypoparathyroidism
– Low magnesium levels
– Deficiency/malabsorption
what are reduced levels of calcium associated with?
- Raised levels (>2.65mmol/l):– NB. Can be a medical emergency, if >3.75, at risk of M.I
– 90% of cases are due to malignancy or
hyperparathyroidism
– Hyperthyroidism
– Dehydration
how do you manage raised levels of calcium?
Manage with fluids initially, if no response
IV bisphosphonates
how is magnesium eliminated?
via the kidney
when is magnesium levels reduced?
– Diuretics
– Liver disease
– Diarrhoea
when are magnesium levels raised?
– Renal impairment
what can low levels of mg be assoicated with and why?
low levels of CA and K- as magnesium helps transport calcium and k+ ions in and out of cells
what are some factors affecting test results?
- How specimens are collected, transported, stored
and processed - When the sample was taken
- Patient age
- Gender
- Nutrition
- Sitting/standing
what are the two examples of potassium binders?
- Patiromer calcium and Lokelma (SZC)
when are potassium binders appropiate?
– Had an acute episode of hyperkalaemia
between 6.0- 6.4 mmol/L
– There is a clinical case to restart withheld
RAASi therapy at a lower dose once resolved
– Potassium on repeat testing is between 5.5 –
6.4 mmol/L
what do you have to monitor with potassium binders?
– Following initiation/dose changes check
potassium 1 – 2 weeks after:
* If <4mmol/L: reduce dose of binder
* If 4 – 5.3mmol/L: continue
* If >5.3mmol/L: increase dose of binder
what is HCT?
– Indicates the proportion of RBC that make up the
blood pool
what is MCV?
– Average size of the RBC
what is MCH?
– Average amount of Hb in a RBC
what is MCHC?
– Average concentration of Hb inside an
average sized cell
what do we consider for microcytic anaemia?
A low RBC (red blood count), Haemoglobin (Hb),
Haematocrit (HCT) and Mean Cell Volume
(MCV) are suggestive of a microcytic anaemia.
what are the causes of iron-deficiency anaemia?
– Inadequate diet
– Deficient absorption
– Blood loss
* Menorrhagia
* GI bleeding
what is the management of microcytic anaemia?
Oral: Iron supplement e.g., ferrous sulphate
200mg OD (65mg elemental iron)
* Continue until normal levels are reached and the
for 3 months thereafter (NICE)
– Parenteral: in presence of malabsorption
e.g., Ferinject®, Cosmofer®
what would indicate macrocytic anaemia in blood results?
In a macrocytic anaemia the mean cell volume is raised
* A raised MCV with a low haemoglobin suggests vitamin B12 or folate deficiency, these should therefore be tested
what is the cause of macrocytic anaemia?
This disease affects all the cells of the body and is due to malabsorption of B12 resulting from atrophic gastritis and lack of intrinsic factor secretion
what are the causes of macrocytic anaemia?
Common features are tiredness and weakness, dyspnoea, sore red tongue, diarrhoea and mild jaundice
how would you treat 1- folate deficiency
2- b12 deficiency?
- Folate deficiency: oral folic acid 5mg daily
- B12 deficiency: replenish stores with hydroxocobalamin (B12):
– 1mg IM alternate days for 2 weeks.
– Maintenance 1mg IM every 3 months FOR LIFE
what is the function of neutrophils?
– Ingest and kill bacteria, fungi and damaged
cells
why would neutrophils rise?
(Neutrophilia) occurs in bacterial
infections
why would neurophils be low?
(Neutropenia) occur in viral
infections, acute leukaemia
what is CRP and what does it indicate?
- Protein produced in the acute phase
response - Synthesised exclusively in the liver
- Rises within 6 hours of an acute event
when do platelets rise?
- Rise: (Thrombocytosis)
– Malignant disease
– Autoimmune disease
– Inflammation
when are platelets low?
- Low: (Thrombocytopenia)
– Drugs
– Leukaemia
what is ESR?
Erythrocyte Sedimentation Rate
(ESR)
* Measure of acute phase response
