Following recommendations from recognized institutions such as ISO and CLIA, more laboratories are using third party controls than ever before. However, great care should be taken when choosing which third party control to use. A number of factors should be considered, and primarily among these is whether the control challenges the complete Clinical Range and the Medical Decision Levels. ISO 15189:2012 states that ‘The laboratory should choose concentrations of control materials wherever possible, especially at or near clinical decision values, which ensure the validity of decisions made’.

Measuring the Complete Clinical Range

It is important to assess the full clinical range of an assay i.e. the range between the lowest and highest results which can be reliably reported. In order to make sure a laboratory instrument is working across the full clinical range, a QC which covers low, normal and elevated concentrations must be used.

Question: “If the full clinical range isn’t covered by QC, how will we know whether patient results which fall outside the range of quality controls are accurately reported?”

What are Medical Decision Levels?

Medical Decision Levels (MDL) are the analyte values at which medical professionals can determine whether a patient may be suffering from a certain condition. The MDL is determined by a consensus of medical professionals and clinical research. Patients’ test results are compared to the MDL and appropriate diagnoses or medical interventions can be made.

For example, the MDL of Glucose can indicate a certain diabetic status:

Analyte	Medical Decision Level	Diagnostic Status
Glucose (fasting)	<100 mg/dL	Non-Diabetic
	100–125 mg/dL	Pre-Diabetic
	>125 mg/dL	Diabetic

Competitor QC

Many QC manufacturers ‘cut corners’ in an attempt to keep costs down, which often results in the sale of controls which do not cover the complete clinical range or vital medical decision levels. Below is an example of the Glucose concentrations present in a competitor control:

Competitor Chemistry Control Level 1 – 68 mg/dL

Competitor Chemistry Control Level 2 – 134 mg/dL

Competitor Chemistry Control Level 3 – 386 mg/dL

In the examples above, the competitor’s level 1 control covers the non-diabetic MDL, but the level 2 control is not within the ‘Pre-Diabetic’ decision range. The level 3 control is also much higher than can be expected for an elevated diabetic patient result (200 mg/dL or more).

Randox QC

Due to the superior manufacturing process used by Randox, QC target values are consistently within the MDL of tests. For example, the Glucose concentrations present in our Liquid Assayed Chemistry Premium Plus control are:

Level 1 – 57 mg/dL

Level 2 – 114 mg/dL

Level 3 – 236 mg/dL

The MDL for Glucose is covered by the Randox control, meaning laboratory professionals can be confident that patient results will be accurately interpreted.

Immunoassay Medical Decision Levels

Controls which cover the MDL can reduce the number of Quality Controls required by laboratories. For example, Randox Acusera Lyophilised Immunoassay Controls contain particularly low levels of TSH, Ferritin and Vitamin B₁₂ in the Level 1 control, eliminating the need for an additional control at extra expense:

Analyte	Medical Decision Level	Randox Level 1 IA Control	Competitor Level 1 IA Control
TSH	0.1 or 0.27 uU/mL	0.15uU/mL	0.37 uU/mL
Vitamin B12	190 pmol/L	174 pmol/L	327 pmol/L
Ferritin	12 ng/mL	11.1 ng/mL	49.6 ng/mL

In this example the competitor offers an anaemia control with lower levels of TSH, Vitamin B₁₂ and Ferritin at an additional cost. With Randox Acusera QC, only one control is required for anemia monitoring and detection.