Screening Assays

Effect of Fibrinogen on PT and PTT

From Alan Neal, Pathlab, NZ. Just wanted a private conversation about the January 11, 2018 Fritsma Factor entry, “POC and Plasma-Based PT/INRs.” I do not agree with the comments made within this article and challenge the logic used. Essentially, if monitoring an enzymatic pathway such as coagulation, with the ‘detector’ being used is fibrinogen to […]

Global Hemostasis Assays

PTT and C-reactive Protein

From Dean Willett, Precision BioLogic Inc. As I read the 11-8-17 comments from Dr. Elman a bit of a lightbulb went off in my head. I’m sure you’ve seen the various publications that demonstrate the effect of C reactive protein (CRP) on APTT assays. Here are: https://www.ncbi.nlm.nih.gov/pubmed/22224499; and https://biblio.ugent.be/publication/5838447/file/6839536. There have been some proficiency samples […]

Lupus Anticoagulant

ISTAT V. Plasma PT/INR

From Diane Treadway: Hi, we had a situation in our cath lab last week. The patient was on the table. They performed an ISTAT PT and obtained 13.0 seconds and 1.1 INR. The patient had had a PT drawn and run by the main lab earlier. Those results on a Stago instrument were 24.2 seconds […]

Screening Assays

Whole Blood PTs

From: Brancaccio Mauro, ICD-Partners, Italy. Is it possible and correct to do the PT on the sangueblood? Hello, Bancaccio Mauro. If I translate correctly, I will take sangueblood to mean whole blood (with thanks to Dave McGlasson for his assistance). Yes, the PT has been established as a whole blood assay using point of care […]

Anticoagulant Therapy

Whole Blood PTTs

From Kirk Guyer, Cascade Technologies: There are whole blood PTT (APTT) assays and there are citrated platelet poor plasma (PPP) PTT assays. What happens in a PPP PTT assay if there are platelets present? Does the PTT result shorten? Can platelets shorten the PTT result in a whole blood PTT assay? I ran a PTT […]

Bleeding Disorders

PT % Activity

This came up in correspondence yesterday and challenged an assumption. The PT is reported in seconds and INR, of course, and it was previously reported as the PT ratio (PTR), which is defined as a ratio of the patient’s PT to the mean normal PT (MNPT). But what is the PT % activity? I have […]

Screening Assays

MELD Score and INR

The model for end-stage liver disease (MELD) score attempts to objectively assesses the severity of chronic liver disease and prioritize liver transplants. The MELD formula is: MELD = 3.78×ln[serum bilirubin (mg/dL)] + 11.2×ln[INR] + 9.57×ln[serum creatinine (mg/dL)] + 6.43; where ln = natural log. MELD score is used to assess 3-month mortality: <9 = 1.9%; […]

Screening Assays

Reference Intervals in Multiple Sites

George received a question from a colleague who is preparing to establish a PT reference interval (RI) for a series of laboratories, large and small that use coagulometers with a range of sophistication from a single manufacturer. All the labs will use a single PT reagent from the manufacturer who distributes the instruments. The key […]

Screening Assays

HCT >55% and Citrate Volume Adjustment

George, is there research available now that states a HCT >55% will not interfere with PT or PTT results? We struggle with the CAP requirement. We use a mechanical based method for PT and PTT within our organization. Hello, and thank you for your question. The current CLSI guideline, Adcock DM, Hoefner DM, Kottke-Marchant K, […]

Screening Assays

Thrombin Time Technique

From Monali Gupta MD, Toronto General Hospital: Hi George, I compliment you for creating such a wonderful website to understand and learn coagulation. The modules are very educative. I have two questions about the DTI assay described in Module 28, Thrombin Time Assay. Why patients’s plasma is diluted in 1:8 or 1:20 in saline? Why pipetting has […]

Anticoagulant Therapy

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George Fritsma is a medical laboratory scientist, educator, and author. George holds faculty appointments with Rutgers University and Michigan State University, and is a member of the International Society on Thrombosis and Hemostasis, American Association of Clinical Chemists, and American Society for Clinical Laboratory Science.

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