EMQ: Clotting (Laboratory Assays)

Options:

A. Collagen induced platelet aggregation assay

B. Dilute Russell Viper Venom Time (DRVVT)

C. Factor IX assay

D. Factor VIII assay

E. Gel electrophoresis of plasma and platelet lysates

F. Plasma Fibrinogen, D-dimers and blood film

G. Ristocetin Induced Platelet Activating assay

H. Serial normal plasma dilution incubations and factor VIII assay

I. Thrombin time and reptilase time

J. Urea clot lysis assay

For each of the following scenarios (1-5) choose the investigation from the list above (a-j) which would be most useful in confirming the diagnosis

Case 1

An 82 year old woman presents with widespread lymphadenopathy, abdominal distension and extensive ecchymoses with an episode of macroscopic haematuria. Blood tests reveal:

Hb: 9.8g/dl, MCV 85fl, WCC: 3.2, Neuts: 1.9 x10⁹/L, LC: 0.9 x10⁹/L, Plt 105x10⁹/L

APTT: 82 (NR 25-35 s), PT: normal. Does not correct with mixing.

Case 2

65 year old man in the intensive care unit with pneumonia requiring non-invasive ventilation, ongoing fevers and hypotension despite 48 hours treatment with intravenous broad spectrum antibiotics. Develops widespread oozing from venepuncture sites and an episode of haematemesis. Liver function test is normal. Mild renal impairment noted with a creatinine of 175mcmol/l. Other bloods:Hb: 9.8g/dl, MCV 85fl, WCC: 20.2, Neuts: 15.9 x10⁹/L, LC: 3.8 x10⁹/L, Plt 82 x10⁹/L

APTT: 82 (NR 25-35 s), PT: 30s (NR 10-15s)

Case 3

A fourteen year old girl is under investigation for menorrhagia and recurrent epistaxis. She is otherwise very well. Blood tests reveal a normal full blood count, liver and renal function but clotting screen reveals:

APTT: 94s (25-35s), PT: 64s (12-15s). Levels correct on mixing

Case 4

A mother is concerned that her baby’s umbilical stump is oozing and he has been irritable. He has had three episodes of fresh blood mixed in with his stool and there is some mucosal bleeding. Full blood count, APTT and PT are entirely normal.

Case 5

An 11 month old boy who is just becoming mobile is brought to the paediatric emergency department with oral cavity bleeding, and epistaxis. He has had a swollen, tender knee for the past two weeks after a minor fall and has numerous bruises.

Answer:

1: Serial normal plasma dilution incubations and factor VIII assay

2: Plasma Fibrinogen, D-dimers and blood film

3: Thrombin time and reptilase time

4: Urea clot lysis assay

5: Gel electrophoresis of plasma and platelet lysates

Explanation:

Acquired haemophilia is an infrequent but recognised paraneoplastic syndrome and inhibitors are usually directed against factor VIII

Coagulopathy in the severely unwell are driven by DIC unless proven otherwise, and the underlying cause should be treated rather than using replacing the consumed clotting factors, unless there is significant clinical bleeding.

Defects in both intrinsic and extrinsic pathways without consumptive coagulopathy or global synthetic defect (unlikely given she is well with normal liver function) suggest either combined factor V and VIII deficiency or dysfibrinogenemia.

Assessment of fibrin generation and ruling out heparin effect would be reasonable prior to factor V and VIII assays. Both conditions are extremely rare.

FXIII deficiency classically presents shortly postpartum with umbilical stump bleeding and a normal clotting profile.

Haemophilia frequently presents at the onset of mobilisation in an infant, with joint bleeds. However the coexisting mucosal bleeding would be unusual and hence VWD should be suspected, with concurrent severe factor VIII deficiency due to the loss of VWF's FVIII binding activity.

Reference:

Medical and Scientific Advisory Council of the National Hemophilia Foundation. The Rarer Clotting Factor Disorders. Special Edition of Haemophilia 2008; 14(6): 1151-1280