What is the reported creatine kinase (CK) result after a 1/10 dilution with saline yields an analyzer result of 980 U/L?

Calculating Diluted CK Result

The correct creatine kinase (CK) result to report after a 1/10 dilution yielding an analyzer result of 980 U/L is 9,800 U/L.

Explanation of Calculation

When performing a dilution of a sample that is out of the instrument's measurement range, the following steps must be taken to determine the actual result:

1. Obtain the analyzer result from the diluted sample (980 U/L)
2. Multiply by the dilution factor (1/10 = 10x dilution)
3. Calculate the final reportable result: 980 U/L × 10 = 9,800 U/L

Laboratory Considerations for CK Testing

Dilution Principles

• When samples exceed the upper limit of the instrument's measurement range, dilution is necessary to obtain accurate results
• The dilution factor must be applied to the measured value to determine the actual concentration in the original sample
• Common dilution ratios include 1:2,1:5,1:10, and higher depending on the expected concentration

Analytical Factors

• Laboratory instruments have specific measurement ranges for each analyte
• For CK, most analyzers have an upper measurement limit that may vary by instrument model
• When results exceed this range, the sample must be diluted to bring the concentration within the measurable range 1

Quality Control Considerations

• The minimum sample volume requirement (0.5 mL in this case) must be met to ensure accurate results
• Saline is an appropriate diluent for CK testing as it does not interfere with the enzymatic reaction
• The dilution must be performed accurately to ensure the validity of the final result

Clinical Significance of Elevated CK

While not directly related to the calculation question, it's worth noting that a CK value of 9,800 U/L represents a significant elevation that may indicate:

• Muscle damage from various causes
• Potential myocardial injury
• Possible rhabdomyolysis

Such elevated levels would typically warrant further clinical investigation based on the patient's presentation and symptoms 1.

Common Pitfalls in CK Result Reporting

1. Failing to apply the dilution factor to the analyzer result
2. Applying an incorrect dilution factor
3. Reporting the diluted result without multiplication
4. Calculation errors when determining the final result

Always verify your calculations when working with diluted samples to ensure accurate patient results are reported.