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Reliability of plasma creatinine measurement in infants and children
Insights
Clinicians should be cautious when using plasma creatinine (Pcr) to estimate glomerular filtration rate (GFR) in children. The SMAC method overestimates Pcr, while the kinetic method shows significant scatter, impacting GFR accuracy.
Area of Science:
- Pediatric Nephrology
- Clinical Chemistry
- Biomarker Validation
Background:
- Plasma creatinine (Pcr) is a common biomarker for estimating glomerular filtration rate (GFR) in pediatric populations.
- Accurate GFR estimation is crucial for diagnosing and managing kidney diseases in children.
- Variability in laboratory methods can affect the reliability of Pcr measurements.
Purpose of the Study:
- To evaluate the reliability of commonly used Pcr measurement methods for GFR estimation in children.
- To compare the accuracy of the kinetic Jaffe technique and the SMAC method against a reference method.
- To identify potential corrections for Pcr overestimation by specific laboratory assays.
Main Methods:
- Comparison of Pcr measurements using a modified Technicon Autoanalyzer reference method.
- Simultaneous analysis of Pcr using a Beckman Astra 8 kinetic Jaffe technique.
- Simultaneous analysis of Pcr using a Technicon continuous flow Jaffe endpoint SMAC method.
Main Results:
- The SMAC method consistently overestimated Pcr by 0.1 mg/dl.
- The kinetic method exhibited significant scatter, with only 37% of GFR values within +/- 25% of the reference method.
- Neither method provided consistent Pcr results below 0.55 mg/dl, a critical range for infants and young children.
Conclusions:
- Subtracting 0.1 mg/dl from SMAC-measured Pcr may yield values comparable to the reference method.
- A corrected Pcr value can be used with established formulas (kL/Pcr) for GFR estimation in different pediatric age groups.
- The kinetic method requires multiple Pcr determinations for reliable GFR assessment due to measurement variability.
Abstract:
Plasma creatinine (Pcr, mg/dl) is often used to estimate glomerular filtration rate (GFR) in children. To establish whether the clinician can rely on the commonly used methods for measuring Pcr, the authors analyzed data from their own modified Technicon Autoanalyzer reference method and compared them to those obtained simultaneously from a Beckman Astra 8 kinetic Jaffe technique or a Technicon continuous flow Jaffe endpoint SMAC method. The SMAC method consistently overestimated Pcr by 0.1 mg/dl, whereas the kinetic method resulted in a large spread around the reference values. Neither laboratory gave consistent results for Pcr below 0.55, the normal range for infants and young children. The SMAC technique tended to underestimate GFR by 20 to 30 percent, whereas the kinetic method resulted in a great deal of scatter (only 37% of the measurements fell within +/- 25% of the values for GFR obtained by the reference method). The results suggest that the subtraction of 0.1 mg/dl from the Pcr measured on the SMAC system would give a value similar to that obtained with the reference method. This correction would permit the use of an estimate of GFR from kL/Pcr, where L is body length in cm and k is a constant (equalling 0.45 in term infants, 0.55 in children, and 0.7 in adolescent boys). The kinetic method requires repetitive determinations of Pcr before any firm conclusions can be drawn about GFR because of the scatter. The reliability of the clinician's laboratory can be tested by sending half the plasma to the laboratory on one day and the other half the next.(ABSTRACT TRUNCATED AT 250 WORDS)