Calculation of Glucose Concentration in Diluted Urine Sample
The glucose concentration in the original urine sample is 500 mg/dL, which should be reported as the final result.
Understanding Dilution Calculations
When a sample is diluted and then measured, the original concentration must be calculated by multiplying the measured concentration by the dilution factor:
- Measured concentration in diluted sample: 50 mg/dL
- Dilution factor: 1/10 (or 10x dilution)
- Calculation: 50 mg/dL × 10 = 500 mg/dL
Laboratory Principles Behind Dilution
The need for dilution occurs when the original sample concentration exceeds the analytical range of the testing method. This is a common practice in clinical laboratories to ensure accurate results 1.
- When the glucose concentration is too high for direct measurement, dilution brings the concentration within the measurable range of the assay
- The Beer-Lambert law applies in spectrophotometric methods, where absorbance is directly proportional to concentration 1
- Dilution maintains this linear relationship while bringing the sample into the analytical range
Quality Control Considerations
When reporting diluted sample results, several factors should be considered:
- Ensure the dilution was performed accurately using calibrated pipettes
- The dilution factor must be properly documented in the laboratory information system
- The final reported result should always reflect the original sample concentration, not the diluted value 2
Clinical Significance of Urine Glucose Measurements
While this question focuses on laboratory calculations, it's worth noting that urine glucose measurements have clinical implications:
- Normal urine typically contains minimal glucose (usually <15 mg/dL)
- Elevated urine glucose (glycosuria) may indicate:
- Diabetes mellitus with blood glucose exceeding the renal threshold
- Renal tubular dysfunction
- Pregnancy-related changes
Potential Sources of Error
When performing dilutions and calculations:
- Inaccurate pipetting can lead to incorrect dilution factors
- Calculation errors when multiplying by the dilution factor
- Failure to document the dilution procedure properly
- Improper mixing of the diluted sample
Summary
The correct result to report is 500 mg/dL, which represents the original glucose concentration in the urine sample before dilution. This calculation follows standard laboratory principles for handling samples that exceed the analytical measurement range of an assay.