Blood Laboratory Tests 1 Flashcards
1
Q
Who performs blood laboratory tests (4)
A
- Phlebotomist
- Nurse
- Healthcare/nursing assistant
- Doctor
2
Q
What are the two main purposes of blood laboratory tests (2)
A
- To provide information on diseases
- To provide information on treatment
3
Q
How do laboratory tests provide information on diseases (5)
A
- Laboratory tests can provide information to support the diagnosis of a disease
- Elevated thyroid stimulating hormone (TSH) would indicate hypothyroidism
- Laboratory tests can be used to monitor disease severity or progression
- Raised urea would indicate more severe community-acquired pneumonia (CURB65)
- A falling white cell count (WCC) and C-reactive protein (CRP) would indicate a infection is resolving
4
Q
How do laboratory tests provide information on drug treatment (5)
A
- Laboratory tests can identify information about the choice of treatments, dosing and side effects
- Abnormal results can arise as a side effect of treatment (e.g. hyponatraemia secondary to carbamazepine)
- Treatments can be selected to treat abnormal results (e.g. calcium carbonate to treat raised phosphate in renal failure)
- Treatment choice and dose can be impacted by laboratory results (e.g. reducing doses based on renal function)
- Therapeutic drug monitoring (TDM) can be used to guide dosing with narrow therapeutic index drugs
5
Q
What is the renal profile
A
Renal profile (also referred to as urea and electrolytes) provides information on the functioning of the kidneys
6
Q
What does renal profile indicate (3)
A
- Fluid status (i.e. dehydrated, overloaded or euvolemic)
- Electrolyte imbalances
- Renal function (i.e. their eCrCl or eGFR)
7
Q
What does the renal profile consist of (5)
A
- Four components
- Sodium (Na)
- Potassium (K)
- Urea
- Serum creatinine (SrCr)
8
Q
What is the importance of sodium (4)
A
- Sodium is the main extracellular cation and therefore closely related to fluid (water) balance
- Sodium homeostasis is regulated by the kidneys
- Antiduiretic hormone (ADH) - aids in regulation
- Aldosterone - aids in regulation
9
Q
What happens with low sodium (4) and what causes it (2)
A
- Hyponatraemia
- confusion
- cerebral oedema
- coma
Caused by:
- Excessive loss of sodium
- Inappropriate water retention
10
Q
What happens with high sodium (3) and what causes it (2)
A
- Hypernatraemia
- confusion
- muscle weakness
Caused by:
- Excessive loss of water
- Excessive sodium intake
11
Q
What is the importance of potassium (3)
A
- Potassium is mainly found inside the cells with only a small proportion in the blood
- Potassium homeostasis is regulated by the kidneys
- Aldosterone - aids in regulation
12
Q
What happens with low potassium (4) an what causes it (1)
A
- Hypokalaemia
- arrhythmias
- weakness
- confusion
Caused by:
- Excessive loss of potassium due to drugs or disease states (e.g. diuretics, Cushing’s, malnutrition
13
Q
What happens with high potassium (2) and what causes it (1)
A
- Hyperkalaemia
- cardiac arrhythmias
Caused by:
- Inappropriate retention of potassium due to drugs or disease states (e.g. ACE inhibitors, renal failure)
14
Q
What is urea
A
Urea plays a major role in nitrogen excretion via the urine
15
Q
What happens with raised urea (5)
A
- Raised urea can identify disease states
- Dehydration
- Renal failure
- Haematemesis
- Chronic cardiac failure
16
Q
What is serum creatine (4)
A
- Creatinine is a by-product of muscle metabolism
- It is produced by the body at an almost constant rate
- almost all creatinine is excreted by the kidneys via filtration
- this makes it an excellent surrogate for renal function
17
Q
What does the quantity of serum creatine produced depend on (4)
A
- Age
- Sex
- Muscle mass (size/sex)
- Ethnicity
18
Q
How is renal function calculated (4)
A
- The most accurate method is with a 24 hour urine collection in combination with SrCr but this is impractical
- In general day-to-day medicine we use equations to estimate renal function based on SrCr
- Cockcroft and Gault equation estimates creatinine clearance (eCrCl)
- Modification of diet in renal disease equation estimates glomerular filtration rate (eGFR)
19
Q
How is creatine clearance calculated
A
eCrCl (mL/min) = (140-age) x weight (Kg) x constant / Serum creatine (µmol/L)
20
Q
What is the creatine constant for males and females (2)
A
Males = 1.23
Females = 1.04
21
Q
What happens with low creatine clearance (2)
A
- The lower the eCrCl, the worse the patient’s renal function is
- the greater the likelihood that medicines will need to be avoided or the doses reduced
22
Q
What is the bone profile (3)
A
- Bone profile looks predominantly at calcium and phosphate levels but also includes other parameters such as albumin
- Calcium is highly protein-bound bound and only unbound (free) calcium is active so it is important to adjust the levels based on albumin (adjusted calcium)
- Calcium and phosphate are important in bone mineralisation and normal function of the central nervous system and muscles
23
Q
What can high calcium cause (8)
A
- Hypercalcaemia
- biliary and kidney stones
- bone pain
- abdominal pain
- nausea and vomiting
- constipation
- polyuria
- cognitive impairment
24
Q
What can cause high calcium (3)
A
- Malignancy
- Disorders of the parathyroid gland
- Overreplacement with calcium supplementation
25
What can low calcium cause (6)
1. Acute hypocalcaemia
2. convulsions
3. arrhythmias
4. tetany
5. paraesthesia
6. In the long term, it can cause osteoporosis
26
What can cause low calcium (4)
1. Inadequate intake of dietary calcium
2. Vitamin D deficiency
3. Disorders of the parathyroid gland
4. Kidney disease
27
What can high potassium cause (3)
1. Hyperphosphatemia
2. often asymptomatic
3. calcium deposits in the soft tissue
28
What can cause high potassium (2)
1. Mainly due to chronic kidney disease
2. Parathyroid disorders
29
What can low potassium cause (3)
1. Hypophosphatemia
2. muscle weakness
3. muscle wasting
30
What can cause low potassium (2)
1. Inadequate oral intake
2. Excessive use of antacids
31
Aubry Jones is a 76-year-old female patient who weighs 50 kg. She takes a medication called alendronic acid 70mg once per week to prevent osteoporotic fractures. Her serum creatinine is 156µmol/L. Calculate her creatinine clearance and advise on the most appropriate course of action for her alendronic acid
eCrCl = 21mL/min
No dosage adjustment is necessary for patients with creatinine clearance greater than 35 ml/min. Alendronate is not recommended for patients with renal impairment where creatinine clearance is less than 35 ml/min, due to lack of experience (EMC).
32
Andrea Folb is an 82-year-old female patient weighing 50kg. She takes Apixaban 5mg BD to treat atrial fibrillation. Her GP has received her blood results from a recent annual check-up. Her creatinine is 156µmol/L. It has been steadily increasing over the last 6 months. The GP is concerned about her dose of apixaban. What would you recommend?
eCrCl = 19mL/min
In patients with severe renal impairment (creatinine clearance 15-29 mL/min)…. for the prevention of stroke and systemic embolism in patients with NVAF, patients should receive the lower dose of apixaban 2.5 mg twice daily (EMC).
