BOF: Clotting (Laboratory Assays)

A 62 year old woman with a previous history of breast cancer is admitted via the emergency department with haematuria and bruising. Blood results show:

Haemoglobin 4.9g/dL, Plts 290 x10⁹/L

APTT ratio 1.9, INR 1.2

50:50 correction of APTT with normal plasma gives a ratio of 1.7

Which of the following descriptions of assay curves would you expect for this clinical picture?

a) Bell shaped

b) Double peaked

c) Non parallelism

d) Right skewed

e) Exponential

Answer:

c) Non parallelism

Explanation:

The diagnosis is suggestive of an acquired inhibitor. Clotting curves when there is an inhibitor are non-parallel, reflecting the non-linear behaviour of the inhibitor to serial dilution. The degree of non-parallelism may be used to determine its potency in Bethesda units.

Reference:

Perry D & Todd T. Practical Haemostasis.com

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