PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 7389115

Prothrombin time standardization and temperature problems.

A Uldall
View original source ↗Export metadata ↓

Abstract

The reaction temperature is crucial for enzymatic reactions. Difficulties in controlling the temperature in the tilt test tube technique for the prothrombin time test are illustrated. An improved detailed description of the technique is suggested for standardization purposes. Mixing of the specimen with the reagent should be done in the water bath. The test tubes should be immersed deeply into the bath. Recording of the temperature in the reaction mixture is recommended. When using plastic test tubes the temperature problems may be greater than with glass test tubes. Some heat denaturation of coagulation enzymes may take place at 37 degrees C. Lowering the temperature of the reaction to 30 degrees C and perhaps photometric recording of the coagulation should be included in a suggested future optimized reference method.

Explore related subjects

Evaluation Studies as TopicHumansProthrombin TimeTemperatureJournal Article

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

A Uldall. 1980-04-11. Prothrombin time standardization and temperature problems.. https://doi.org/10.1016/0009-8981(80)90228-4

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed1998

A set of van der Waals and coulombic radii of protein atoms for molecular and solvent-accessible surface calculation, packing evaluation, and docking.

We analyze the contact distance distributions between nonbonded atoms in known protein structures. A complete set of van der Waals (VDW) radii for 24 protein atom types and for crystal-bound water is derived from the contact distance distributions of these atoms with a selected group of apolar atoms. In addition, a set of Coulombic radii for polar atoms is derived from their contacts with water. The contact distance distributions and the two sets of radii are derived in a systematic and self-consistent manner using an iterative procedure. The Coulombic radii for polar atoms are, on average, 0.18 A smaller than their VDW radii. The VDW radius of water is 1.7 A, which is 0.3 A larger than its Coulombic radius. We show that both the VDW and the Coulombic radii of polar atoms are needed in calculating the molecular and solvent-accessible surfaces of proteins. The VDW radii are needed to generate the apolar portions of the surface and the Coulombic radii for the polar portions. The fact that polar atoms have two apparent sizes implies that a hydrophobic cavity has to be larger than a polar cavity in order to accommodate the same number of water molecules. Most surface area calculations have used only one radius for each polar atom. As a result, unreal cavities, grooves, or pockets may be generated if the Coulombic radii of polar atoms are used. On the other hand, if the VDW radii of polar atoms are used, the details of the polar regions of the surface may be lost. The accuracy of the molecular and the solvent-accessible surfaces of proteins can be improved if the radii of polar atoms are allowed to change depending on the nature of their contacting neighbors. The surface of a protein at a protein-protein interface differs from that in solution in that it has to be generated using at least two kinds of probes, one representing a typical apolar atom and the other a typical polar atom. This observation has important implications for docking, which relies on surface complementarity at the interface.

Evaluation Studies as Topic↗
PubMed1998

A practical guide to Papanicolaou smear rescreens: how many slides must be reevaluated to make a statistically valid assessment of screening performance?

BACKGROUND: The question of the minimum number of Papanicolaou (Pap) smear slides that must be rescreened to draw statistically valid conclusions regarding the accuracy of screening often is raised. No method for generating answers in varying laboratory circumstances has achieved widespread application; standard statistical sample size calculations may represent such a resource. METHODS: A series of tables was constructed to display minimum required numbers of rescreens, with each table representing differing hypothetical laboratory circumstances. To use each table, assumptions must be specified in advance as to prevalence of abnormality, definition of error, baseline false-negative proportions (FNPs) of performance, and a degree of increase in FNPs that is considered a departure from baseline warranting concern, among others. RESULTS: The authors constructed four sample tables displaying minimum numbers of slides that must be rescreened in differing specified laboratory scenarios. Depending on assumed conditions and predetermined levels of satisfactory and unsatisfactory accuracy, the range of numbers is very broad (38-10,000). One example representing likely conditions indicates that 1040 slides must be reexamined; in another scenario, a sample size of 300 is sufficient. CONCLUSIONS: The minimum number of rescreened slides needed to draw statistically valid conclusions regarding Pap smear screening accuracy can be calculated using standard statistical methods. However, a number of assumptions must be detailed in advance. The authors offer this as a practical guide and a continuation of a general inquiry regarding Pap smear error rate measurement and display. The use of these tables raises at least as many questions as it answers, but still may represent a significant advance. Future efforts at further numeric characterization of aspects of Pap smear screening performance are warranted to enable rational decision making when performance is examined in the course of quality assurance, and during quality control and regulatory activities. [See editorial on pages 127-9, this issue.]

Evaluation Studies as Topic↗