Stability Duration of a Normal Control Pool for Prothrombin Time and Activated Partial Thromboplastin Time Prepared in the Hematology and Blood Bank Service of the Yaoundé University Teaching Hospital, Cameroon

Abstract

Prothrombin Time (PT), also called Quick’s Time (QT), is a coagulation test expressed in seconds, measured in the presence of tissue thromboplastin and calcium ions. Similarly, Activated Partial Thromboplastin Time (APTT) is measured in the presence of phospholipids, an activator, and calcium ions. These two tests are among the most commonly used in hemostasis. Their execution absolutely requires plasma samples used as quality controls, whether commercial or prepared locally (“pooled” in the laboratory).
This descriptive study aimed to determine the stability duration of an in-house control pool for PT and APTT tests, prepared in the laboratory of the Hematology and Blood Bank service of the Yaoundé University Teaching Hospital, Cameroon.
Plasma was collected after centrifugation, mixed, and then frozen at a temperature of -30 °C to preserve the coagulation factors, especially the most labile ones. The plasma pool was then aliquoted, stored at -30 °C protected from light in a domestic freezer, and kept for a period of two weeks. A portion of the pool was tested within four hours of collection: 30 PT and APTT analyses were performed.
The assay was performed manually using the tube tilt method. The means obtained were 12.71 seconds for PT and 30.66 seconds for APTT. The acceptability limits (mean ± 2 standard deviations), calculated from the standard deviation, were 11.38 to 14.04 seconds for PT and 27.96 to 33.37 seconds for APTT.
The plasma pool was then analyzed daily in duplicate. The average of the results for each day was plotted on a Levey-Jennings chart and interpreted according to Westgard rules. The results showed that the stability duration of the normal control pool is eight (8) days for PT and seven (7) days for APTT.
In a context marked by a recurrent shortage of quality control reagents, for various logistical and economic reasons, these results offer a reliable alternative to commercial control samples, which are often expensive or unavailable. The use of locally prepared control pools could thus compensate for stock-outs of normal or pathological control reagents supplied by manufacturers.