Platelets (Sources: Revision notes) Flashcards
When should you consider investigating a decrease in platelet count?
If < 100 or falls by >30%
What are the common and less common but important causes of thrombocytopenia in ICU pts?
Sepsis DIC Haemodilution Haemofiltration and extracorporeal circuits Drugs e.g. G2a/3b inhibitors, chemo Excess alcohol Hypersplenism Liver disease Post-surgery e.g. bypass Macrophage activation syndrome Blood bourne viruses e.g. HIV, CMV Folate deficiency Myelodysplasia Less frequent are TTP, HUS, HIT, ITP, HELLP, malaria
How should you investigate low platelets in ICU patients?
R/V history, exam and medications Blood film - may be diagnostic, can exclude clumping B12, folate D-dimer LFTs coag screen Renal function LDH bHCG HIV Bone marrow aspirate
Whos guidance should we follow with regards to platlet transfusion in the UK?
The joint United Kingdon Blood Transfusion and Tissue Transplantation Services Professional Advisory Committee (JPAC)
According to JPAC what are the triggers for platelet transfusion in the critically unwell?
Non-bleeding pts without sepsis or haemostatic abnormalities - not indicated
Prophylaxis in non-bleeding pts with severe sepsis or haemostatic abnormality - 20 x 10(9)/L
DIC with bleeding - >50
Plt dysfucntion with non-surgically correctable bleeding - may bleed despite plts count normal - give one pool and rpt according to clinical response
Major haemorrhage - >75 if multiple traum or trauma to the CNS
Describe heparin-induced throbocytopenia
Rare
Immune mediated
Occurs between 5 and 10 days post heparin exposure, but can occur within hours if the pt has had previous heparin exposure
Plt count is typically 50-80
It’s a prothombotic state and can manifest as necrotic skin leisons and arterial and venous thrombosis
How should you investigate whether a patient may have HIT?
Calculate a pre-test probability score - e,g, the Warkentin 4T score
A low score reliably excludes HIT
A moderate score should prompt further investigation
- a HIT screen involves an ELISA test for anti-heparin PF4 antibodies and a functional screen
How should you manage suspected HIT?
Heparin should be stopped
Switch to non-heparin anti-coagulation e.g. danaparoid, lepirudin, valirudin or argatroban
Platelet transfusion is contra-indicated in HIT
What is thrombotic thrombocytopenia purpura?
A rare disease
Significant mortality
It’s a thrombotic microangiopathy (TMA)
It has an autoimmune aetiology associated with low levels of ADAMTS-13
May be associated in some cases with HIV infection, pregnancy and some drugs e.g. quinine, clopidogrel, aciclovir
How does TTP manifest clinically?
Thrombocytopenia
Microangiopathic haemolytic anaemia (MAHA)
Microvascular thrombosis and its consequences e.g. cerebrovascular comp-lications, cardiac ischaemia, renal dysfunction; haematuria
How do you investigate for TTP?
Check ADAMTS-13 levels
How is TTP managed?
Management in a specialist centre Plasma exchange Immunosuppression Organ support if required Platelet transfusion is contraindicated
Describe the Warkentin 4T scoring system
Used for pretest probability scoring in HIT
- Thrombocytopenia - 2 if > 50% fall in plts, 1 if 30-50% fall
- Timing - 2 if onset within 5 days (or <1 day if heparin within last 30 days), 1 if > day 10 or timing unclear
- Thrombosis - 2 if proven new thrombosis, skin necrosis; 1 if progressive or recurrent thrombosis
- Other cause for platelets to fall - 2 non evident, 1 possible
What is haemolytic uraemic syndrome?
HUS is predominantly a renal TMA
Characterised by MAHA, AKI and throbocytopenia
Typical HUS is associated with diarrhoea (usually bloody) and infection with shiga toxin-producing pathogens e.g. E.Coli 0157
How is HUS managed?
Supportive
Plasma exchange and immunosuppression
