- Last Update On : 2013-01-28
Reference ranges for the same methods or instruments may differ between laboratories and buying viagra online safe geographic areas for the following reasons:
- Operating conditions are different.
- Criteria for selection of generic viagra overnight deliver western union healthy subjects are different.
- Geographic areas have different temperature, altitude, barometric pressure, humidity, and time zones.
- Subject preparation and sample collection may differ.
Because of these differences, reference ranges should be established locally whenever a new test is introduced or an existing method is changed. NCCLS recommends testing at least 120 patient samples for establishment of a statistically significant reference interval. Other experts recommend a minimum of 200 samples to ensure stable lower and upper reference limits.
It may be necessary to tramadol free shipping subdivide reference ranges into partition groups. For example, hemoglobin reference ranges should be established by gender and age while cortisol ranges s