How to Identify PK or HMWK Deficiency

Here is a paraphrase of a question I (Geo) received on 4-3-26: “We recently evaluated a patient with an isolated prolonged APTT that corrected on mixing study. The patient has no history of bleeding and no significant family history of bleeding disorders. FVIII, FIX, FXI, and FXII assays were within normal limits. In view of these findings, we are considering a possible PK/HMWK deficiency and would like to perform an APTT with prolonged incubation. Do you have any suggestions?

Frequent expert contributor Bob Gosselin offered this suggestion:

1. Prewarm APTT reagent and CaCl2
2. Add 50 uL of sample to 50 uL of APTT reagent
3. Incubate for 10 minutes at 37^oC (waterbath)
4. Add 50 uL of CaCl2, – record clotting time.

• Have you ever used Mr. Gosselin’s PTT incubation procedure?
• Is there a source for PK– and HMWK-deficient plasmas?
• What purpose is served by assaying for PK and HMWK?
  

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From colleague Dr. Larry Brace: If after following our usual protocols for identification of factor deficiencies, we are left with PK/HMWK deficiency, I would advise the clinician that further testing would be for academic purposes. Usually, the clinician did not pursue further testing.

See Dr. Favaloro’s response below for sources of PK and HMWK-deficient plasma.