# Practical-Haemostasis.com

## A Practical Guide to Laboratory Haemostasis

### Introduction

This section covers many of the tests that were outlined in the section on 'Miscellaneous tests' - some questions do cross over into some of the other sections.

Question 1

You are provided with prothrombin times using two different thromboplastins on a number of patients stably anticoagulated on warfarin as well as several normal healthy individuals.
One thromboplastin is the WHO rabbit reference material and the other is an 'in-house' rabbit material you have prepared in your laboratory.

 Plasma Sample PT [s] WHO Reference Preparation PT [s] In-House Preparation 1 32 15.5 2 46 16 3 50 19.5 4 46 16 5 15 12 6 43 16 7 13 12 8 45 18.5 9 32 15.5 10 13 11 11 55 18 12 48 17 13 13 11 14 14 12 15 55 18 16 55 20 17 29 15

A. What is the ISI of this home made material?
B. Would you use this thromboplastin in your laboratory? If not, why not?

If you plot the PTs of the samples against each other and the derive the slope of the curve then you should end up with an ISI of ~4.7. Remember the WHO reference preparation is plotted on the Y axis and the 'in-house' preparation on the X-axis. From this graph the slope of the curve can be derived and this is the ISI of the thromboplastin preparation. This is a rough estimate of the ISI and a more sophisticated approach would be employed in reality.

In this case the ISI is 4.7 and in practice this is unacceptable [!]. Most laboratories might accept an ISI of 1.4 but in practice most recombinant thromboplastins have an ISI of <1.2.

Question 2

From the data shown in the attached graph derive the ISI (roughly) for thromboplastin. If you click HERE you can open the graph in a new window.
The WHO Reference thromboplastin has an ISI of 1.0. Points A, B and C are designed to help you.

The slope of the curve is derived from [A-C]/[B-C] and this gives a slope [ISI] of 125/110 = 1.14. This is a much more acceptable ISI than that shown in Q1.
Remember the INR is derived from the formula: [PT patient/PT control]ISI

Using the ISI that you derive from this graph, what are the INRs of the following samples:

Sample PT INR
1 13s 1.14
2 23s 1.91
3 35s 3.09
4 18s 1.58
5 67s 6.48
Reference plasma 13s -

Question 3
A 20-year-old woman is 32/40 weeks pregnant. She attends the antenatal clinic for a routine check up. You are asked to see her because of the following results:

 Test Patient Reference Range Hb 10.1g/dL 11.5-13.5 g/dL WCC 6.2 x 109/L 6 - 10 x 109/L Platelets 80 x 109/L 150 - 400 x 109/L MPV 13.1 fL 7.5-9.2 fL

1. What would you do immediately and what investigations would you request?
2. What are the possible diagnoses?
The possibilities include Gestational Thrombocytopaenia, Immune Thrombocytopaenia but you should exclude artefactual thrombocytopaenia by requesting a citrated [or similar] platelet count. You must request a blood film to look for evidence of platelet clumping, to exclude other causes of thrombocytopaenia [e.g. May Hegglin anomaly] and to look for red cell fragments might suggest a diagnosis of TTP, HELLP or some other microangiopathic haemolytic anaemia [MAHA.]
A screen for Antiphospholipid antibodies and an ANA would not be unreasonable tests particularly if this was the first platelet count that was available to you. It would be important to review whether the platelet count had been normal or low in the past when this lady was not pregnant as this clearly gives important diagnostic clues [but of course this information may not be available to you.] You should think about rarer causes of a low platelet count if there is a life-long history of thrombocytopenia and in particular if there are other associated clinical problems that might for example suggest a MyH9 gene mutation of if there is a family history of thrombocytopaeni
a.

1. You request:
a. A platelet count using citrate as an anticoagulant - the platelet count is 78 x 109/L.
b. A blood film is reported as normal and in particular no platelet clumps are seen.
c. A screen for anti-phospholipid antibodies is negative.
d. The ANA is positive and the ENA shows the presence of Anti-Ro and Anti-La antibodies.

What will you do next?

The finding of a positive ENA and anti-Ro/Anti-La antibodies raises the possibility that this lady has an underlying immunological cause for the thrombocytopaenia. The anti-Ro/Anti-La antibodies are associated with a risk of congenital heart block in the baby and you should highlight this with the obstetricians/fetal medicine team.
You should repeat the ANA and ENA screen and arrange to see this lady again to monitor the platelet count.

You should have noticed in the data that was provided that the MPV was raised. This suggests that the cause of the low platelet count is likely to be increased peripheral destruction rather than a failure in platelet production. In individuals in whom the thrombocytopaenia in due to a primary bone marrow problem the MPV is usually low. In gestational thrombocytopaenia the MPV is usually raised. There are, of course, some inherited macrothrombocytopaenias and you a family history is, as always, essential.

At 36 weeks the platelet count is 62 x 109/L.
What advice will you give to the obstetricians and the obstetric anaesthetists?

The platelet count on most machines is derived from the platelet size and in individuals with an elevated MPV, the true platelet count may be underestimated. For these reasons it is of value to check an immunological platelet count. This involves labelling the GpIIb/IIIa receptor and these are then counted by flow and so it counts platelets independently of their size.
In this lady the immunological platelet count was 93 x 109/L. In general if we assume normal platelet function, a count > 80 x 109/L is considered safe for delivery and for spinal/epidural anaesthesia. A platelet count of 50-80 x 109/L is safe for delivery but spinal/epidural anaesthesia should be avoided. A count of 50 x 109/L requires treatment in advance of delivery to raise the count.
Remember - if you cannot exclude ITP in this lady there is a possibility that the baby may have a low platelet count. You should advise that a cord platelet count is taken at delivery and if it is low it is likely to fall further reaching its nadir at Day 3 following delivery. The obstetricians should be cautious at delivery and avoid a forceps delivery, ventouse delivery, fetal scalp sampling and fetal scalp electrodes.

Don't forget this lady also has Anti-Ro antibodies and so you must consider the baby in this scenario both to exclude congenital heart block which may require immediate pacing but also because the baby may be thrombocytopenic due to maternally-transferred IgG.

Finally whilst we consider that this woman has Immune thrombocytopaenia based indirectly upon the findings of Anti-Ro antibodies, the possibility of a functional platelet defect cannot be entirely excluded and may influence how you mange this woman and the advice you give to the obstetricians/obstetric anaesthetists
.

Question 4

A 23-year-old man is investigated for a possible bleeding disorder whilst living in Paris. He has a bleeding time performed and this is found to be significantly prolonged at 26 minutes (NR: <10 minutes). He returns to the UK and seeks your advice as to the significance of the prolonged Bleeding Time.

a. Briefly outline the principles of the bleeding time
b. What abnormalities would explain the prolonged bleeding time?
c. What additional tests would you request?
d. Is this test still commonly performed?

The Bleeding Time is performed as outlined previously.
The BT is dependent upon [other than performer error] the number of platelets and their function, Von Willebrand Factor levels and function and whether there is a problem with the vascular endothelium/collagen. Remember individuals taking anti-platelet agents will have a prolonged BT. There is considerable inter- and intra-performer error when undertaking a BT and for these reasons it is only rarely performed today.

In the context of a prolonged BT it is sensible to check the FBC/platelet count and to measure FVIII and VWF levels.

1. You decide not to repeat the BT but he scores highly on your structured bleeding questionnaire. You request some additional investigations which show:

 Test Patient Reference Range PT 11.2 11-14s APTT 51s 23-35s FVIII:C 0.12 IU/mL 0.5 - 1.5 IU/mL VWF:Ag 0.11 IU/mL 0.5 - 1.5 IU/mL VWF:RCo 0.12 IU/mL 0.5 - 1.5 IU/mL

The FBC is normal.

1. What is the diagnosis?
The most likely diagnosis is Type 1 VWD and which accounts for ~80% cases of VWD.
2. Does this explain the prolonged bleeding time?
Yes - the lack of VWF means that platelets cannot be anchored to the vascular endothelium at sites of damage including that induced by performing the BT.
3. What is French for the Bleeding Time?
Le temps de saignement [!]

Question 5

Briefly explain the principles of the Activated Clotting Time and the Thrombin Time.

The Activated Clotting Time is discussed HERE and the Thrombin Time HERE.

1. What factors can affect the ACT?
See Activated Clotting Time.
2. What factors can affect the thrombin time?
See Thrombin Time.
2. Why do we use the ACT and not the thrombin time to monitor patients on cardio-pulmonary bypass?
The high concentrations of unfractionated heparin used to anticoagulate patients on CPB results in a thrombin time is unclottable and so it cannot be used to monitor these patients.

Question 6

A 64-year-old man undergoes an aortic valve replacement. Prior to coming off bypass he is given protamine sulphate to reverse the unfractionated heparin. His BP falls and he becomes profoundly hypotensive.

1. What is protamine sulphate and how does it work?
Protamine Sulphate was originally isolated from the sperm of salmon and other fish but is now more commonly produced by recombinant technology. It is a highly cationic protein that binds strongly to heparin [primarily unfractionated heparin] neutralising its effect. Protamine sulphate in overdose has a weak anticoagulant activity. It efficiently reverses the anticoagulant activity of unfractionated heparin but less so that of Low Molecular Weight Heparin [LMWH]. Some individuals who have a fish allergy can develop anaphylaxis when exposed to protamine. Anaphylaxis has also been reported in some individuals who have had a vasectomy and some individuals who in the past have received protamine-containing insulin - the latter is rarely if ever used today.
1mg of Protamine Sulphate will reverse 100 IU of UFH.

2. What do you think might have happened?
This patient a fish allergy and developed anaphylaxis following reversal of the UFH used during bypass.

Question 7
A 56-year-old man with a long history of COPD is admitted for surgery.
His pre-operative investigations show a Hb of 19g/dL and an Hct of 0.58 .

 Test Patient Reference Range PT 20s 11-14s APTT 47s 23-35s

1. What might explain these findings and what would you do next?

This patient has an elevated Hb and Hct. As a consequence when his blood is collected into citrate for clotting tests, there is less plasma than normal and therefore the concentration of citrate in the plasma is higher than in individuals with a normal haematocrit. When the plasma is re-calcified as part of the PT and APTT, it only partially re-calcifies because of the high citrate concentration and therefore the clotting times are prolonged. This can be overcome by using a nomogram that corrects for the Hct and reduces the amount of citrate used as an anticoagulant.

Question 8

Outline the mechanism of action of tranexamic acid and DDAVP.

1. Tranexamic acid [TA]: TA binds to and blocks the high affinity lysine binding sites on plasminogen [and subsequently plasmin when plasminogen is activated] preventing the binding of plasmin and plasminogen to the fibrin clot or to fibrin monomers.
Human plasminogen contains 4 to 5 lysine binding sites with low affinity for tranexamic acid and 1 with high affinity and it is the high affinity site of plasminogen that is involved in its binding to fibrin.
Tranexamic acid is excreted in the urine and its use is contraindicated in patients with haematuria.
TA has a of ~3.1 hrs. It is approximately 8-10X more active than EACA.

2. DDAVP:DDAVP - in a dose dependent manner, DDAVP increases FVIII and VWF release from endothelial cells. Interestingly DDAVP also causes the release of T-PA and formed the basis for a test similar to the venous occlusion test and known as the DDAVP stimulation test.
DDAVP is of value in individuals with mild haemophilia A and Type 1 VWD. It may be of value in Type 2A, 2M and 2N VWD although in the latter the rapid clearance of FVIII due the lack of a stabilising VWF results in a very short T½. DDAVP is sometimes used in individuals with non-specific platelet function defects prior to minor surgery. It is of no value in patients with severe haemophilia A or Type 3 VWD and as it does not increase the levels of FIX in plasma, it is of no value in Haemophilia B.

DDAVP is a potent anti-diuretic nonapeptide and fluid retention leading to hyponatraemia is a recognised side-effect. For these reasons, DDAVP should not be administered more than once every 24 hours. DDAVP also exhibits tachyphylaxis that is a reduction in the amount of FVIII and VWF that is released from endothelial cells with repeated dosing.
DDAVP can be given intravenously, subcutaneously or intra-nasally. DDAVP has been given to women at the time of delivery as the anti-diuretic nonapeptide affect of DDAVP is mediated through the V2 vasopressin receptors whereas in the uterus vasoconstriction and uterine contraction are related to the V1 receptor.

Question 9
A 45-year-old female presents with spontaneous proximal DVT. She is anticoagulated with initially a low molecular weight heparin and subsequently warfarin with a target INR of 2.5.

Shortly after starting warfarin she complains of bruising and presents 5 weeks later to Accident and Emergency with a large haematoma in her right calf. Her investigations on admission are shown below:

 Test Patient Reference Range INR 2.3 1.0 APTT 117s 28-34.5s Fibrinogen (Clauss) 3.9 g/dL 2-4 g/dL Haemoglobin 12.2g/dl 13.5-16.2 g/L Platelets 298 x 109/L 150-400 x 109/L

1. What additional tests might you request and why?

The APTT is disproportionately prolonged compared to the INR suggesting a problem with factors VIII, IX, XI or XII. We presume the PT and APTT were normal prior to commencing anticoagulants [- all patients commencing anticoagulants should have a PT and APTT performed] and therefore, this is an acquired abnormality.

1. You request some factor assays:

 Test Patient Reference Range FVII 20 u/dL 50 - 150 u/dL FIX <1 u/dL 50 - 150 u/dL FX 23 u/dL 50 - 150 u/dL FV 112 u/dL 50 - 150 u/dL

What do you think may provide an explanation for these findings?

The patient has disproportionately low FIX levels compared to the other clotting factor and in particular to FX and FII both of which are Vitamin K dependent clotting factors. You might think about screening for a FIX inhibitor [rare] by performing an inhibitor screen.

Sequence analysis of the F9 gene in this patient identifies a mutation [Ala-10Thr] at position Ala-10 within the propeptide for FIX.
1. Comment upon these findings.
This mutation interferes with the recognition site for gamma-glutamylcarboxylase the enzyme that is involved in carboxylation of the glutamic acid residues of the vitamin K dependent clotting factors. In the case of the Ala-10Thr mutation the mutation results in a reduction in affinity for the carboxylase enzyme and makes the protein more sensitive to warfarin.

2. How would you manage this patient?
There are a number of possibilities:
a. You could switch this patient to a Low Molecular Weight Heparin
b. You could switch to one of the oral direct thrombin inhibitors.

Question 10
A 67-year-old man with no previous history of note requires an aortic valve replacement. He has a pre-operative screen performed and this shows the following:

 Test Patient Reference Range PT 13s 11-14s APTT >120s 28-34.5s Fibrinogen (Clauss) 3.9 g/dL 2-4 g/L Thrombin Time 14s 11.5-13.5s Platelets 358 x 109/L 150-400 x 109/L

1. What would you do next?

1. On a structured bleeding questionnaire he scores 0. He has undergone a number of dental procedures with no problems.
2. Factor VIII, IX and XI assays are normal. What is the most likely diagnosis?

The most likely diagnosis is that he has a contact factor deficiency such as FXII. You should, therefore request a FXII assay.

He has a Factor XII <1 IU/dl. The cardiac surgeons ask what treatment he needs for his severe Factor XII deficiency and the cardiac anaesthetists ask you how they will manage heparinisation when he goes onto bypass and can they use the ACT to monitor the dosing of heparin?
How will you respond to these questions?
1. You can re-assure the surgeons that he will not bleed as a consequence of his Factor XII deficiency and that he does not need 'Factor XII replacement therapy.'
2. Managing bypass is more difficult as the ACT will be prolonged before any unfractionated heparin is introduced into the circuit. In this situation you need to monitor the degree of anticoagulation by measuring anti-Xa levels. This will require close collaboration between cardiac anaesthetists/pump technicians and the haemostasis laboratory. You will also need to establish what Anti-Xa levels you need to achieve appropriate anticoagulation.

Question 11
A 56-year-old woman is admitted thorough Accident and Emergency having been found confused at home by her partner.

Investigations show:

 Test Patient Reference Range PT 14s 11-14s APTT 35s 28-34.5s Fibrinogen (Clauss) 2.1 g/dL 2-4 g/L Thrombin Time 14s 11.5-13.5s Hb 8.6 g/dL 7.3 g/dL Platelets 23 x 109/L 150-400 x 109/L WCC 11.2 x 109/L 6-10 x 109/L LDH 2342 U/L <450 U/L Serum creatinine 356 µmol/L 52-90 µmol/L

1. What additional tests would you request?

1. You request a blood film which is shown below:

What is the most likely diagnosis?

The clinical history together with the thrombocytopenia, elevated LDH and the presence of fragmented red cells on the peripheral blood film should alert you to a diagnosis of Thrombotic Thrombocytopenic Purpura [TTP].

Questions might include new drugs, the possibility of HIV, pregnancy and other risk factors for TTP. Congenital TTP due to an inherited mutation in the ADAMTS13 gene can occasionally present for the first time in adult life.

1. The diagnosis is TTP.

What tests might you request to support this diagnosis?
The most logical test is an ADAMTS13 assay together with a screen for an inhibitor.

You request ADAMTS 13 studies. Comment upon the results of the tests which are shown below>:

 Test Patient Reference Range ADAMTS 13 Activity <5% 66–126% IgG Anti-ADAMTS13 85% <4.2%

These results are consistent with TTP due to an inhibitor of ADAMTS13.

Question 12
A 45-year-old woman is on treatment for pulmonary TB and develops a large abdominal haematoma. Laboratory investigations show:

 Test Patient Reference Range PT 14s 11-14s APTT 35s 28-34.5s Fibrinogen (Clauss) 4.2 g/L 2-4 g/L Thrombin Time 13s 11.5-13.5s Platelets 387 x 109/L 150-400 x 109/L PFA-100 [Collagen:ADP] Normal closure times

1. What additional tests would you request?

You request a factor XIII screen. Shown below are the results of a FXIII screening test using 5M urea.

 Patient: Clot lysis in 45 minutes Patient Plasma + normal plasma [50:50 mix] No clot lysis after 24 hours Control plasma No clot lysis after 24 hours

What does this suggest and what is the cause of this?
These results indicate defective clot lysis and raises the possibility of Factor XIII deficiency. Factor XIII inhibitors have been reported in patients receiving Isoniazid as in this case.
This is, therefore, a case of acquired FXIII deficiency due to an inhibitor arising in a patient receiving Isoniazid. Stopping the Isoniazid is usually associated with resolution of the inhibitor.

Factor XIII inhibitors are rare but their presence should be considered in individuals who present with an acquired bleeding disorder but in whom the PT/APTT/ platelet function tests are normal.

Question 13

A 67-year-old male is admitted to the Coronary Care Unit with unstable angina. He undergoes an emergency coronary angioplasty and receives in addition to 5000 units of unfractionated heparin, Abciximab to prevent re-occlusion of the coronary artery. 3 days after the procedure he is noted to be bruising and his platelets are found to be 5 x 109/L having been 189 x 109/L at the time of his admission.

i. What are you going to do
The differential diagnosis here is either Abciximab-induced thrombocytopaenia or heparin-induced thrombocytopaenia. The latter [HIT] is unlikely after a single dose of unfractionated heparin even if this patient had a history of HIT although in practice most physicians would recommend a HIT screen and avoid further UFH. The diagnosis is, therefore Abciximab-induced thrombocytopaenia. The treatment involves the administration of platelets and these may require for be given for 4-5 days until the thrombocytopaenia resolves.

ii. What do you think has happened
This patient has Abciximab-induced thrombocytopaenia. This arises due to the formation of human anti-chimeric antibodies. In some individuals these antibodies appear to be naturally occurring. In others they occur following the administration of Abciximab and when the patient is subsequently exposed to it and usually with 30 days of the first exposure.

iii. What is Abciximab
Abciximab is chimeric murine-human monoclonal anti-glycoprotein IIb/IIIa inhibitor and which prevents the subsequent binding of fibrinogen , von Willebrand Factor and other adhesive molecules.

Question 14
A 23-year-old man is referred for investigation of prolonged bleeding after dental extraction. Shown below are the results of his preliminary tests. Comment upon the results of these tests and suggest other other that you think would be of value.

 Test Patient Reference Range PT 11s 11-14s APTT 45s 28-34.5s Fibrinogen (Clauss) 3.8 g/L 2-4 g/L Thrombin Time 13s 11.5-13.5s Platelets 387 x 109/L 150-400 x 109/L PFA-100 [Collagen:ADP] 155s 60-133s

1. What additional tests would you request?

On the basis of the prolonged APTT you request the following Factor Assays:

 Test Patient Reference Range FVIII 16 u/dL 57 - 141 u/dL VWF:Ag 40 u/dL 50 - 150 u/dL VWF:Act 31 u/dL 50 - 150 u/dL RIPA [0.5mg/ml] Absent Absent

What do you think may provide an explanation for these findings?

You request genetic tests and these show:

1. MLPA [Multiplex ligation independent probe amplification] - heterozygous gene deletion spanning exons 17-52 of the VWF gene.
2. Heterozygous single base change leading to a p.Arg854Gln mutation [Exon 20.] The latter has been reported in several cases of 2N VWD
.

1. Comment upon the results of these genetic tests.
He appears to have a partial gene deletion that encompasses the FVIII binding site and so leads to defective binding of FVIII and in addition he has a reported 2N VWD mutation. The combination leads to a pseudohomozygous 2N phenotype [and hence the low FVIII levels] but in addition a defective VWF allele [and hence the low VWF levels]

2. Do they provide an explanation for the observed phenotype.
Yes!

Question 15
A 57-year-old man is transferred to ITU following coronary artery bypass grafting. He has a 'routine' post-operative clotting screen performed which shows:

 Test Patient Reference Range PT 11s 11-14s APTT 34s 28-34.5s Fibrinogen (Clauss) 2.2 g/L 2-4 g/L Thrombin Time >120s 11.5-13.5s Platelets 187 x 109/L 150-400 x 109/L

1. What do you think might provide an explanation for these results and what would tests would you like to perform?

1. You think that this might be due to the presence of unfractionated heparin as this patient has just come off bypass.

2. You request a Reptilase time which is normal at 13s.

24 hours later you repeat the Thrombin Time which comes back as >60s. This patient is not receiving heparin in any form and the sample has not been taken from a heparinised line.

3. What do you think might provide an explanation for these findings?

The prolonged thrombin time but normal Reptilase time is not consistent with the presence of unfractionated heparin as this would cause a prolongation of both. It would also be unusual to have a Thrombin Time >120s and a normal APTT. This raises the possibility of either a defective fibrinogen molecule [but we know the fibrinogen in a Clauss assay is normal] or there is a problem with the assay.

You repeat the thrombin time but using human thrombin rather than bovine thrombin and the test is normal.

How do you explain these findings?
The thrombin time using bovine thrombin is prolonged because the patient has anti-bovine antibodies. These can occur 'naturally' or following exposure to bovine thrombin.

Question 16
A 47-year-old man is see in the Emergency Department with a 2 week history of easy bruising and more recently of a prolonged epistaxis. His past medical history was unremarkable, he had not commenced any new drugs and there was no family history of note.

He had a full blood count performed together with the results of some 'basic' clotting tests. Shown below are the results of his preliminary tests.

Comment upon the results of these tests and suggest other investigations that you think would be of value in reaching a diagnosis.

 Test Patient Reference Range PT 15.9s 11-14s APTT 21.3s 28-34.5s Fibrinogen (Clauss) 0.6 g/L 2-4 g/L D Dimer >60,000 ng/mL 0-230 ng/mL Platelets 14 x 109/L 150-400 x 109/L Hb 7.2 g/L 11.5 -15.5 g/dL WCC 276 x 109/L 5-16 x 109/L

1. What additional tests would you request?

You are concerned about the FBC and request a blood film - these are shown below:

1. Comment upon the results of the blood films?
The blood films are consistent with a diagnosis of Acute Promyelocytic Leukaemia [M3]. Subsequent cytogenetic and molecular studies confirmed the PML-RARa rearrangement of the t(15;17) translocation.

2. Why do patients with this particular problem bleed?
The mechanism is poorly understood although there is on-going work in this area. Mechanisms include:
- Tissue Factor expression on the surface of APL blast cells
- A cysteine procoagulant detected on APL blast cells that can activate Factor X independently of Factor VIIa
- Enhanced expression of Annexin II on the surface of APL blast cells which can act as a cell surface receptor for plasminogen and t-PA and so up regulate fibrinolysis
- Elastase, Cathepsin-G and proteinase-3 are present in the granules of APL blast cells and can directly degrade a number of coagulation factors including Fibrinogen and VWF.

Question 17
A 67-year-old man presents to his GP with a short history of easy bruising and epistaxes. He had not started any new drugs recently and he had no history suggestive of a bleeding disorder. Examination was unremarkable apart from a systolic ejection murmur consistent with aortic stenosis.

He has a full blood count performed together with some 'basic' coagulation tests. Shown below are the results of these tests.

Comment upon the results of these tests and suggest other investigations that you think would be of value in reaching a diagnosis.

 Test Patient Reference Range PT 12s 11-14s APTT 33s 28-34.5s Fibrinogen (Clauss) 3.6 g/L 2-4 g/L Platelets 314 x 109/L 150-400 x 109/L Hb 11.2 g/L 11.5 -15.5 g/dL WCC 7.6 x 109/L 5-16 x 109/L

What additional tests would you request?

You arrange for some additional tests to be performed.
The results are shown below:

 Test Patient Reference Range Factor VIII 89 U/dL 57 - 141 U/dL VWF:Ag 75 U/dL 50 - 150 U/dL VWF:RCo 38 U/dL 50 - 150 U/dL PFA 100 [Collagen:ADP] 155s <113s

On the basis of these tests what additional tests would you request?

The history of is recent onset and the diagnosis is likely therefore to be an acquired problem rather than an inherited one. The PT and APTT are normal but there are no VWF assays and no platelet function tests.
We are told that the patient has not started on any new drugs.

You repeat the Von Willebrand Factor assays and confirm the low VWF:RCo at 37 U/dL.
The PFA 100 is still prolonged at 152s

What additional tests will you now request?

This suggests an abnormality of Von Willebrand Factor and the normal VWF:Ag would suggest that this is a Type 2 defect.