Practical-Haemostasis.com

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Data Interpretation:
Factor Assays

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Question 1

Plot the following factor X assay data [from a PT-based assay] and calculate the factor X levels for the four plasma samples. The concentration of FX:C in the reference plasma was 94% (94 IU/dl).

 

	Dilutions
	1/10	1/20	1/30	1/40	1/80	1/100	1/1000
Reference plasma	25s		32s			38s	59s
Patient 1	35s					54s	82s
Patient 2	22s		28s			34s
Patient 3	180s			182s			182s
Patient 4	30s	34s		39s	45s

All clotting times are in seconds.

Click this LINK to take you to a site that will allow you to generate and print your own graph paper.

A. If the concentration of FX in the reference plasma was 112% (112 IU/dl) - what would your answers be?

B. If the concentration of FX in the reference plasma was 0.90 IU/ml - what would your answers be?

 

Question 2

Plot the following factor VIII data and calculate the factor VIII levels. The concentration of FVIII in the reference plasma is 94 IU/dl.

	1/5	1/10	1/20	1/40	1/80	1/100
Reference Plasma		41s	53	66		82
Patient 1		55s		79		96
Patient 2	108	120
Patient 3		70	82		107
Patient 4		30	42	55		71

All clotting times are in seconds.

Click this LINK to take you to a site that will allow you to generate and print your own graph paper.

If the concentration of FVIII in the standard was 0.89 IU/ml what would your answers be?

 

Question 3

Part 1:

A 23-year-old woman of Iranian descent presents to her GP with menorrhagia. The GP requests a coagulation screen and the results of this are shown below:

Test	Patient	Reference Range
PT	34s	11-14s
APTT	82s	23-35s
Fibrinogen	2.9g/L	1.5-4.0g/L
Thrombin Time	13s	10-13s

 

1. How would you proceed with the investigation of this patient?

 

Part 2:

Shown below are the data for a factor V assay and a factor VIII assay.

Plot the data and derive the concentrations of these two factors.

Click this LINK to take you to a site that will allow you to generate and print your own graph paper.

 

Factor V Assay

Dilutions	Clotting Time (s) Control	Clotting Time (s) Patient
1/10	23	60
1/20	38	92
1/40	59	160

NB Control Factor V concentration 85 IU/dl.

 

Factor VIII Assay

Dilutions	Clotting Time (s) Control	Clotting Time (s) Patient
1/10	35s	50s
1/20	43s	57s
1/40	50	64
1/100	59s	74s

NB Control Factor VIII concentration 90 IU/dl

 

Part 3:

The diagnosis of combined deficiency of factor V and VIII is confirmed.

1. What is the molecular basis underlying this disorder?
   
   

Question 4

A 7-year-old boy is investigated with prolonged bleeding following dental surgery. A coagulation screen is requested and he is found to have a prolonged PT and APTT.

Click this LINK to take you to a site that will allow you to generate and print your own graph paper.

i. What factor assays would you request and why?
ii. Shown below are the data for a PT-based factor X assay. From this data derive the patient’s factor X level.
iii. Is there any value in performing an APTT-based FX assay?
iv. There are 5 methods for assaying FX - what are they?

 

Dilutions	1/10	1/20	1/40	1/80	1/100
Standard	20s	24s	28s	34s	35s
Patient	35s	42s		59s	62s

NB Factor X Standard 110 IU/dl.

 

Question 5

A developmentally normal 2-year-old girl is referred with a history of easy bruising, haematoma formation after vaccination and more recently of a probable left knee haemarthrosis. A coagulation screen shows:

                                   

Test	Patient	Reference Range
PT	12s	11-14s
APTT	90s	23-35s
Fibrinogen	2.9g/L	1.5-4.0g/L
Thrombin Time	13s	10-13s
Full Blood Count	Normal

i. What factor assays would you request and why?
ii. Shown below are the data for a 1-stage factor VIII assay. From this data derive a factor VIII result for the patient.

Click this LINK to take you to a site that will allow you to generate and print your own graph paper.

Dilutions	1/10	1/20	1/40	1/100
Standard Reference Plasma	29s	49s	59s	72s
Patient	68s	78s	88s	101s

NB Factor VIII Standard 104 IU/dl.

 

What are the possibilities to explain these findings?

 

Question 6

An 18-year-old male patient with factor VII deficiency has a factor VII assay performed.

1. Calculate the FVII levels in the patient.

Click this LINK to take you to a site that will allow you to generate and print your own graph paper.

All clotting times are in seconds
FVII standard: 115 IU/dl.

2. The results of his parents are also shown. Calculate their FVII levels.
3. What can you infer from these family studies?

 

Question 7

A 56-year-old male with moderate Haemophilia A diagnosed 16 years ago requires surgery.

Part 1:

Shown below are the results of his pre-operative clotting screen:                               

Test	Patient	Reference Range
PT	12s	11-14s
APTT	33s	23-35s
Fibrinogen	2.9g/L	1.5-4.0g/L
Thrombin Time	13s	10-13s
Full Blood Count	Normal

1. Are you surprised by these results?

2. What might explain this?

 

Part 2.

Below is data from a 1-stage APTT FVIII assay and a chromogenic FVIII assay. Derive the FVIII:C from these two assays.

[Click this LINK to take you to a site that will allow you to generate and print your own graph paper.

 

1-stage FVIII:C Assay

	Dilutions
	1/10	1/40	1/160
Reference Plasma	35	42	47
Patient	37	44	49

 

Chromogenic FVIII:C Assay

	Concentration [IU/dl]
	150	100	50	0
Absorbance 405nm Reference Plasma	0.47	0.32	0.19	0.04

Absorbance Patient: 0.06

 

1. What is the basis for a chromogenic FVIII Assays?

2, How do you explain these findings.

3. What is the molecular basis for this?

 

Question 8

Show in the table below are the data for a factor XI assay performed on 2 separate plasma samples [Plasma 1 and Plasma 2.]

Plot the data for the FXI reference plasma [FIX:C 100%] and draw a best fit line. For the two plasma samples plot the data but do not attempt to draw a best fit line.

1. Calculate the FXI levels for each of the dilutions in the two plasma samples.
2. Explain your findings.
3. What would you do next ?

	Dilutions
	1/10	1/20	1/40	1/100	1/160
Reference Plasma	30	33	37	42
Plasma 1	40	43	47	52
Plasma 2	37	38	40	42	43

[Nb Plot the data on Log-Lin paper]

 

Calculate the FXI:C for each of the dilutions for Plasma 1 and Plasma 2.

How would you explain these findings and what would you do next?

 

Question 9

Calculate the Bethesda titres for each of the following plasma samples.

 

Sample	Plasma Dilutions	Residual FVIII	Titre [BU/ml]
1	Undiluted	70%
2	Undiluted	40%
3	Undiluted	0.5 IU/ml
4	Undiluted	0.6 IU/ml
5	Undiluted	45 IU/dl
6	1/5 1/10 1/20	33% 55% 68%
7	1/20 1/40 1/80	35% 55% 68%
8	1/320 1/640 1/1280	0.30 IU/ml 0.52 IU/ml 0.65 IU/ml

 

Question 10

A 56-year-old woman of Jewish ancestry is referred for an aortic valve replacement (AVR). Her pre-operative screening tests show:

           

Test	Patient	Reference Range
PT	13s	11-14s
APTT	61s	23-35s
Fibrinogen	2.9g/L	1.5-4.0g/L
Thrombin Time	13s	10-13s
Full Blood Count	Normal

 

What tests would you perform next?

The results of a FXI assay are shown below:
Calculate the FXI levels in the plasma sample.

Dilutions	Clotting Time (s) Reference Plasma	Clotting Time (s) Patient Plasma Sample 1
1/10	26	36
1/20	29	39
1/100	38	48

NB Reference Factor XI:C concentration 100%.

 

This lady has an uneventful AVR. She is supported through the surgery and the post-operative period with FXI concentrate. 12 days later she begins to ooze from her wound. A repeat clotting screen shows:

                     

Test	Patient	Reference Range
PT	11.8s	11-14s
APTT	85s	23-35s
Fibrinogen	2.9g/L	1.5-4.0g/L
Thrombin Time	12s	10-13s
Full Blood Count	Normal

 

Shown below is the raw data for a repeat FXI assay. Calculate the FXI level in this plasma sample. What do you think has happened?

 

Dilutions	Clotting Time (s) Reference Plasma	Clotting Time (s) Patient Plasma Sample 1
1/10	26	50
1/20	29	54
1/100	38	62

NB Reference Factor XI:C concentration 100%.

 

An inhibitor assay is undertaken. The FXI:C assay data is shown below.

Calculate the residual FXI:C. This was based upon a 1:20 dilution of plasma.

What is the inhibitor level.

Dilutions	Clotting Time (s) Reference Plasma	Clotting Time (s) Patient Plasma Sample
1/10	26s	29s
1/20	29s	32s
1/100	38s	41s

NB Reference Factor XI:C concentration 100%.

 

Question 11

A 23-year-old male is diagnosed with mild haemophilia A (VIII:C 12 IU/dL) following prolonged bleeding after dental surgery. He requires further dental surgery and you elect to treat him with DDAVP and tranexamic acid.

1. How do DDAVP and tranexamic acid work – illustrate with a diagram if you find this easier.

2. What are the side effects of DDAVP and how do we minimise these?

 

Question 12

A 45-year-old male is referred for further investigation following the finding of an abnormal coagulation profile. He had contacted his GP having developed bruising and epistaxes.
His health had previously been excellent apart from a recent chest infection for which he had been prescribed amoxicillin.

Test	Patient	Reference Range
PT	45s	11-14s
APTT	79s	23-35s
Fibrinogen	3.2g/L	1.5-4.0g/L
Thrombin Time	13s	10-13s
Full Blood Count	Normal

Outline how you would investigate this patient. Give the reasons behind these investigations.

Part II

The results of relevant factor assays are shown below: Factor II 132u/dl [Reference range: 50-150u/dl]
Factor V 2u/dl [Reference range: 50-150u/dl]
Factor X 89u/dl [Reference range: 50-150u/dl]

1. What do you think has happened and why.

2. Are there any other tests you might request?

3. Why does this problem arise?

4. How would you manage this patient?

 

Question 13

What are the differences between a 1-stage and a 2-stage factor VIII assay?

Why might you request a 2-stage factor VIII assay?

 

Question 14

A 3-year-old boy with severe haemophilia B (IX:C<1IU/dl) has a poor response to factor IX concentrate. An inhibitor screen is performed which is positive.

1. Outline the basis of the inhibitor screen.

2.From the data provided establish the factor IX inhibitor titre in this patient.

	Patient Plasma Dilutions
	1/5	1/10	1/20
Residual FIX:C	33%	55%	68%

Question 15

Plot the following data from a patient with suspected Factor V deficiency. What is the factor V level?

	Dilutions
	1/10	1/20	1/40	1/100
Control	50s	68s	95s	135s
Patient	80s	115s	160s	No Data

Control FV:C 85 U/dL.

 

Click HERE for the Answers!

Try to resist the temptation to look at the answers before you work through all the questions!

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Updated: 07-Oct-2009