Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (747 page)

   BT is not prolonged in coagulation disorders such as the hemophilias.

   Limitations

   These include the operator’s variability in technique, limited precision, accuracy, reproducibility, and also variability in the same patients at different times. “In vitro” BT equipment, such as platelet function analyzer (PFA 100), is better standardized and has better reproducibility.

   
Many health care organizations have discontinued the use of BT entirely
.

BLOOD GAS, pH

   Definition

   pH is the negative logarithm of the hydrogen ion concentration and is an index of acidity and alkalinity of the blood. It changes nonlinearly masking magnitude of acid–base disorders. The hydrogen ion concentration is dictated by the ratio of two quantities: the HCO
₃
− concentration, which is regulated by the kidneys, and the PCO
₂
, which is controlled by the lungs.

   Normal range:

   Arterial: 7.35–7.45

   Venous: 7.31–7.41

   Use

   To evaluate acid–base disorders

   Interpretation

Increased In

   Metabolic alkalosis (plasma bicarbonate excess)