What investigations are used to diagnose asthma?
- Spirometry
- FEV1/FVC ratio < 70 % indicative of obstructive airway disease - Bronchodilator reversibility test
- FEV1 improvement of 12% - positive
- + increase in volume of 200 ml
- + obstructive spirometry for diagnosis of asthma - FeNo
- > 40 ppb
- under 17s > 35 ppb - positive peak flow variability for diagnosis of asthma
- if there is diagnostic uncertainty with spirometry + BDR
- positive peak flow variability for diagnosis of asthma
Diagnosis of asthma in adults with symptoms suggestive of asthma:
- a FeNO level of 40 ppb or more with either positive BDR or positive peak flow variability or bronchial hyperreactivity, or
- between 25 and 39 ppb and a positive bronchial challenge test, or
- positive BDR and positive peak flow variability irrespective of FeNO level.
General Ix for COPD
Spirometry
Additional investigations:
- CXR: hyperinflation, bullae, flat hemidiaphragm - FBC - anaemia or polycythaemia - BMI
If marked improvement in symptoms in response to inhaler therapy - consider alternate diagnosis
Diagnosis of COPD
- performed at diagnosis
- to reconsider diagnosis
- monitor disease progression
- measure post-bronchodilator spirometry to confirm diagnosis of COPD
Post-bronchodilator FEV1/FVC < 0.7
FEV1 (of predicted)
> 80% : Stage 1 - Mild - symptoms should be present to diagnose COPD in these patients
50-79% : Stage 2 - Moderate
30-49% : Stage 3 - Severe
< 30% : Stage 4 - Very severe
DIfferentiating between asthma + COPD
When diagnostic uncertainty, identify asthma if:
- a large (over 400 ml) response to bronchodilators - a large (over 400 ml) response to30 mgoral prednisolone daily for2 weeks - serial peak flow measurements showing 20% or greater diurnal or day-to-day variability.
What is D-dimer?
- usually used to exclude venous blood clot
- negative predictive value - if it is negative, extremely unlikely to be a blood clot
- If it is positive - this could be due to many differentials.
When is D-dimer requested?
- DVT
- symptoms of leg pain, tenderness, oedema, discolouration
- PE
- Symptoms: SOB, cough, lung related chest pain
- DIC
- Symptoms: mucosal bleeding, bruising, N & V
Interpret D-dimer
- normal - most unlikely to be clot
- positive - indicated there is clot but not the location
- normal range < 0.50 µg/mL
What can result in false negative d-dimer?
anticoagulant therapy
Indication for sputum culture
- Respiratory tract bacterial infection
- monitor effectiveness of treatment
When is sputum culture indicated?
cough, fever, muscle aches, fatigue, trouble breathing, chest pain, confusion
Sampling procedure of sputum culture
cough up phlegm not saliva
Analysis of sputum culture
- indication of which bacteria
- antibiotic sensitivity
Indication for PCR
Viral infection
Sampling for PCR
Nasal swab
What is sweat chloride testing used for?
Diagnos Cystic Fibrosis
Indication for sweat chloride testing
Infant or child w:
- frequent resp infections - chronic cough - persistent diarhoea - foul-smelling bulky greasy stools - malnutrition
How is sweat chloride test sample taken?
Sample - sweat sample collected using special sweat stimulation procedure
- pilocarpine - chemical stimulates the sweat glands is used
Result of sweat chloride test in CF carriers
Normal
What is Acid-fast bacillus smear and culture used for?
Diagnosis of TB
- Identifies mycobacterial infection
- Monitor effectiveness of treatment
Indications for Acid-fast bacillus smear and culture
- long lasting cough
- sputum contains blood
- Positive TB skin or blood teat
- weight loss
- fever
- chills
- weakness
Sampling for Acid-fast bacillus smear and culture
- 3 separate spit (sputum) samples
- collected early in the morning on different days
What does the Acid-fast bacillus smear and culture look for?
- looks for presence for bacteria called acid-fast bacilli - rod shaped
- can be seen and counted under microscope
What is Bordetella pertussis culture used for?
Diagnosis of Whooping cough
