PROPRIETARY INFORMATION
CONFIDENTIAL MATERIAL
Not for Customer Distribution
Assays/Reagents
AEROSET
®
System Troubleshooting Guide
131
94816-107—November 2004
Observed Problem
Frequently Asked Questions (FAQ)
Question/Comment
Response
MULTIGENT
®
Direct LDL does not match the
Friedewald (calculated) LDL.
• As the triglyceride level rises above
400 mg/dL, the Friedewald calculation
underestimates the true LDL concentration.
• In the Friedewald, an erroneously
calculated LDL result can be compounded
by an error measuring total cholesterol,
triglyceride, or HDL.
On a proficiency survey, the peer comparison
looks OK—but the comparison to the
reference method (ultracentrifugation) has a
significant bias.
• Matrix effects are not uncommon with
proficiency material, especially lipids.
• Results should be evaluated against the peer
group for LDL.
• Comparison of the homogeneous LDL to
ultracentrifugation should be performed
using fresh serum samples.
The doctor is questioning the LDL result (high
or low).
• Was the test repeated on the original serum
or plasma sample?
• Are other lipid results available? Is the
triglyceride level greater than 1,293 mg/dL?
• Sample integrity—verify the serum/plasma
sample was stored at 2 to 8°C if not
analyzed immediately.
• Was plasma used? Plasma in citrate tubes is
not acceptable; use plasma in EDTA,
sodium, or lithium heparin tubes.
A bias (negative or positive) is seen with CAP
proficiency survey results.
Verify the customer is reporting under CAP
Code 225: Liquid Selective Detergent.
Imprecision
Probable Cause(s)
Corrective Action(s)
Problem with sample probe (
e.g.
, not
aligned, bent, etc.).
1. Run multiple reps of sample to confirm the
problem exists.
2. If problem still exists, troubleshoot the
sample probe. Refer to
Section 10,
Troubleshooting and Diagnostics
of the
AEROSET System Operations Manual
.