Investigations Flashcards
What does an FBC (full blood count) measure?
- haemoglobin
- platelets
- white cell count (WCC)
What does haemoglobin lvls tell us in an FBC?
- low Hb is anaemia: found in chronic inflammation or blood loss
- microcytic anaemia (small Hb): suggests iron deficiency
- macrocytic anaemia (big Hb): suggests auto-immune disease
What do platelet levels tell us in an FBC?
- low platelets (thrombocytopenia): suggests problem with bone marrow (seen in SLE and APLS)
- high platelets (thrombocytosis): often occurs in active inflammatory disease (reactive thrombocytosis)
What does white cell count (WCC) tell us in an FBC?
- high lvls: suggests infection, inflammation, or due to steroid use
- leukopenia (low lymphocytes): feature of SLE, connective tissue disease, or due to anti-rheumatic drugs
What do ESR (erythrocyte sedimentation rate) lvls tell us?
- Inflammatory marker: seen more in chronic inflammation/infection
- increased levels with increased levels of plasma proteins (eg. immunoglobulins and fibrinogen)
- (ESR= rate at which RBCs sediment over an hour)
What do CRP (C-reactive protein) lvls tell us?
- CRP is an acute phase protein made in the liver
- Inflammatory marker: lvls rise in a non-specific way (typically takes 6-10 hrs after an inflammatory event to increase)
- note: CRP responds more rapidly than ESR to changes in inflammation
What do U&Es (urea and electrolytes) tell us?
- raised urea suggests renal failure or dehydration
- note: chronic NSAIDs use can cause interstitial nephritis (inflammation of kidneys)
What do LFTs (liver function tests) tell us? (in regards to MSK related conditions) and what MSK drug used for RA treatment is hepatotoxic?
- raised alkaline phosphatase is seen in Pagets disease
- (alkaline phosphatase is found in both the liver and bone)
- note: some drugs used for MSK problems (eg. methotrexate) are hepatotoxic
What do uric acids lvls tell us?
- lvls are high in many patients with gout (but not a differential)
What do calcium levels tell us?
- hypocalcaemia: occurs in osteomalacia and vitamin D deficiency
- hypercalcaemia: may suggest malignancy, sarcoid, and excess PTH production
What do creatine kinase (CK) lvls tell us?
- creatine kinase (CK) is a muscle enzyme
- lvls increase in response to muscle injury (eg. trauma, inflammation)
What do complement protein lvls tell us?
- complement proteins are activated in response to injury/inflammation
- they bind to vessel walls and tissue when activated, this can lead to low serum lvls of C3 and C4 (seen in SLE)
What do antiphospholipid antibodies tell us and what are they associated with?
- lupus anticoagulant and anticardiolipin antibodies are found in antiphospholipid syndrome (APLS)
- associatiated with thrombosis (VT/AT) and recurrent miscarriages
Why would a blood film be requested?
- to look at specific cells (RBCs, WBCs, platelets, leukaemia, malaria)
What does rheumatoid factor tell us?
- around 75% of patients with RA have a +ve rheumatoid factor antibody
- Rf is an antibody directed against Fc fragment of IgG
What does anti-CCP (cyclic citrullinated peptide antibody) tell us?
- anti-CCP is found in patients with RA
- note: more specific than rheumatoid factor
What does procalcitonin lvls tell us?
- Inflammatory marker (more specific for bacterial infections)
- note: often used for an acute hot joint
What does antineutrophil cytoplasmic antibodies (ANCA) tell us?
- c-ANCA (cytoplasmic) bind to PR3: found in patients with granulomatosis with polyangiitis (Wegeners granulomatosis)
- p-ANCA (perinuclear) bind to MPO: found in patients with microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome)
- (PR3 and MPO are neutrophil enzymes)
What are the antinuclear antibodies (ANAs) associated with specific diseases? (there are 8)
- note: anti-Scl-70 (topoisomerase)
What are the 3 things you can do with synovial fluid analysis?
- look at macroscopic appearance (colour)
- gram stain and culture (if suspected septic arthritis)
- polarised light microscopy (to assess the presence of crystals in fluid)
What does the macroscopic appearance (colour) of synovial fluid tell us? (yellow and clear, blood-stained, cloudy, frank pus, chalky)
- yellow and clear: normal
- blood-stained: haemarthrosis or trauma from aspiration
- cloudy: increased WCC from infection/inflammation
- frank pus: infection
- chalky: gout crystals, occasionally cholesterol crystals
Why would we do a gram stain/culture on synovial fluid and what might make it more difficult to detect organisms?
- if suspected septic arthritis (or infection of the joint)
- note: may be more difficult to detect organisms if antibiotics have been given before an aspirate has been obtained
You perform polarised light microscopy on a synovial fluid sample, what would the appearance of the crystals look like in gout and what would it look like in pseudogout?
- Gout: negatively birefringent needle-shaped (monosodium urate crystals)
- Pseudogout (CPPD): weakly positive birefringent rhomboid-shaped (calcium pyrophosphate dihydrate crystals)
Why would a biopsy be taken?
- important in assessment of bony lesions in suspected cancer
- muscle biopsies are sometimes needed for suspected myositis
What are x-rays useful for and how many views should you take?
- used to view bone (mainly to assess fractures and arthritis)
- two views (usually AP and lateral)
Why would ultrasound be used?
- to investigate soft tissue injuries (eg. tears and effusions)
- advantages: safe, cheap, portable, allows a dynamic assessment
When would a CT (computed-tomography) scan be used?
- can give a 3D view
- sometimes used for complex fractures
When would an MRI (magnetic resonance imaging) be used?
- gives a very detailed view of soft tissues and bone marrow
How does an isotope bone scan work and what can it tell us?
- radioactive tracers are injected into body and taken up physiologically by bone
- image shows areas of increased uptake: usually growth plates, arthritis, fractures, metastases, infection, and Paget disease
- note: isotope bone scans are sensitive but not specific (not used for diagnosis)
What is a DEXA (dual energy x-ray absorptiometry) scan used for?
- measures bone density
- used to diagnose osteoporosis and osteopenia
- (T-score <-2.5 is osteoporosis, T-score <-1 is osteopenia)
What is a PET (positron emission tomography) and what is it used for?
- nuclear medicine scanning technique that can be used to observe metabolic activity within the body
- can be useful for identifying active inflammation in specific tissues (eg. large vessel vasculitis, occult infections)
