Immunology (MedEd) Flashcards
A 19 year old man who has sex with men presents to the GUM clinic three weeks after he has had unprotected sex with another man.
He is extremely worried he may have caught HIV as he usually has protected sex with condoms.
What is the most appropriate test to provide this patient with an accurate diagnosis?
A. Rapid point of care test
B. CD4 count
C. Viral PCR
D. Viral load
E. 4th generation Antigen and antibody test
E. 4th generation Antigen and antibody test
According to the British HIV association (BHIVA) guidelines, the median window period for this test is 17.8 days (ranging from 13-26 days). Therefore, given this patient is three weeks post-exposure , this is the most appropriate test to see if this patient has contracted HIV. It is a serological blood test that requires venepuncture
Not: A. Rapid point of care test
This is known as the finger prick test and only needs a spot of blood to be conducted. However, antibody detection has a three month (90 day) window period and so, if the initial result were negative, would need to be repeated three months after the initial exposure in order to display a true results. Therefore, this would not be an appropriate choice for this patient
A 32-year-old man presents to the emergency department with a 2-week history of shortness of breath, which has worsened to the point that he felt breathless on the short walk into the department this morning. He has noticed a nonproductive cough that started around the same time. On questioning, he reports feeling generally run down, and has experienced night sweats and 4 kg of weight loss over the past month.
On inspection of his chest, a red, vesicular unilateral rash is noted on the left side of his back in a band-like pattern. He describes a slight burning sensation in this area and describes a previous episode of similar presentation on his right side some weeks ago. On further inspection, a collection of small raised pink lesions with central umbilication is visible over his trunk. Palpation of the neck reveals has a unilateral 1-cm soft nontender, mobile cervical lymph node.
A set of observations is taken:
BP 118/83 mmHg
Temperature 38.3 °C
HR 83 bpm
O2 saturation in air was 95% initially, but has improved to 98% on repeat
RR 19 breaths per minute
A chest X-ray is arranged, which shows no obvious abnormalities. What is the most likely underlying cause of this man’s presentation?
A. Community-acquired pneumonia
B. Hodgkin lymphoma
C. Tuberculosis
D. Heart failure
E. Primary HIV infection
E. Primary HIV infection
This man has presented with a 4-week history of progressively worsening shortness of breath consistent with Pneumocystis jirovecii pneumonia. This is a common opportunistic infection in immunocompromised individuals, such as those with untreated HIV. It is important to have a low threshold for suspicion of HIV, even in absence of obvious risk factors. The other factors indicative of HIV infection in this case include a subacute history of weight loss and night sweats, cervical lymphadenopathy, and dermatological features, including recurrent shingles and molluscum contagiosum.
Not C. Tuberculosis
This is a reasonable differential for this man’s presentation; however, tuberculosis would more likely result in a chronic productive cough, with purulent or bloodstained sputum and findings on chest X-ray.
what is p24 antigen test used for? when?
An antigen test checks your blood for an HIV antigen, called p24.
The p24 antigen test is accurate 11 days to 1 month after getting infected
what is seroconversion?
Seroconversion is a sign that the immune system is reacting to the presence of the virus in the body. It’s also the point at which the body produces antibodies to HIV. Once seroconversion has happened, an HIV test will detect antibodies and give a positive result.
HIV clinical progression
when does seroconversion occur?
Up to six weeks after getting HIV, most people experience a short one- or two-week illness called a seroconversion illness eg flu-like symptoms, myalgia
-differential: EBV
What is an allergic reaction?
Immune reaction to something harmless eg nuts
define atopy:
tendency to develop IgE antibodies against innocuous antigens (allergens)
what type of T cells responsible for atopy?
Th2 cells
what is sensitisation?
sIgE antibody presence & binding to mast cells (Fc receptor on surface, irreversible binding) & basophils
-can be sensitised but not allergic
-If two IgE molecules on the surface of mast cells recognise antigen and cross-link, then this will lead to mast cell activation and in servere cases, anaphylaxis.
what are some mediators stored in granules?
- histamine (H1-4R)
- proteases eg tryptase (can be measured in blood)
- proteoglycans eg heparin
- cytokines eg TNFa
what are some consequences of mast cell release?
- vasodilation
- smooth muscle spasm (contraction)
- increased permeability
- nerve endings: itch
define allergy:
sensitisation + typical reaction history &/or positive provocation
what tests can be used to diagnose allergy?
- Skin prick tests
-positve response: wheal >2mm greater than negative control (negative control: dilutant, positive control: histamine) - Quantitative specific IgE to pollutant allergen (blood RAST: (Radioallergosorbent test):
-measure levels of IgE in serum against a particular antigen
name of swelling over the skin
urticaria (itchy, bumpy rash)
name of swelling over mucosal surfaces/softer tissues (eg eye, lips, tongue, throat)
angioedema
how does allergy affect different bodily systems?
- skin/mucosal surface; urticaria, angioedema
- GI system: oedema of intestines; vomiting, cramps, diarrhoea
- Heart: vasodilation–> low BP–> compensatory tachycardia, palpitations, pre-sycope, LOC, empty ventricle syndrome; pulmonary vasospasm, a decreased left ventricular preload, and decreased cardiac output (obstructive shock). It is theorized that all of these effects on the CV system come together to cause an “empty ventricle syndrome” when a patient in anaphylaxis is placed in an upright position (don’t put patients in upright posture
- Resp system: bronchoconstriction (smooth muscle contraction–> SOB, wheeze), itch, sneezing, nasal discharge, voice changes, stridor, asphyxiation
why is it not recommended to put patients in upright position during empty ventricle syndrome?
this can increase the workload on the heart and worsen their condition. In an upright position, blood is pulled downward by gravity, which can cause blood to pool in the lower part of the body, decreasing the amount of blood returning to the heart. This can put additional strain on the heart, which is already struggling to pump effectively.
define anaphylaxis
skin changes (urticaria/angioedema) + A, B & C problem
what are the 2 things needed to treat anaphylaxis (updated guidelines)?
- Adrenaline
- Fluids
(no steroids, no antihistamines, no bronchodilators)
how does adrenaline treat anaphylaxis (mechanisms)
a1: vasoconstriction (increases peripheral vascular resistance, decreases mucosal oedema
b1: inotropy, chronotropy
b2: bronchodilation, decreases exocytosis (stops release of granule contents)
how to treat anaphylaxis in outpatient?
-lift legs up (returns blood to right ventricle)
-epipen
anaphylaxis algorithm:
why does someone need to be kept in hospital for 6 hours after anaphylaxis?
biphasic reaction