Carryover

Carryover occurs when residual analyte from a high-concentration specimen contaminates the next specimen measured — producing a falsely elevated result in what should be a low-concentration sample. Even a small amount of carryover can be clinically significant for analytes where the difference between normal and abnormal results is narrow, or where the high and low concentrations span a large dynamic range.

The Carryover module uses a structured 21-specimen sequence to detect and quantify contamination from high-concentration specimens into subsequent low-concentration measurements. A carryover estimate is calculated with a 95% confidence interval and compared against a user-defined or automatically computed error limit to determine pass/fail.

When to Use This Module

Carryover testing is required or strongly recommended in the following situations:

New instrument implementation — Before a new analyzer enters routine use, carryover must be evaluated to confirm that residue from high-concentration specimens does not contaminate subsequent low-concentration results.
Analytes with wide dynamic range — Tests where patient samples routinely span a large concentration range — such as HbA1c, glucose, therapeutic drugs, or tumor markers — are at higher risk for clinically significant carryover contamination.
After major maintenance or component replacement — Repairs or replacements involving sample handling pathways (probes, tubing, cuvettes) can alter the instrument's carryover characteristics and should be followed by a carryover assessment.
Reagent lot changes — Changes in reagent formulation may affect the instrument's washing efficiency or non-specific binding, potentially altering carryover behavior.
Unexplained high results in low-concentration patients — If clinical staff report unexpectedly elevated results in patients known to have low analyte concentrations, carryover should be evaluated as a potential cause, particularly if those specimens were processed after high-concentration samples.