Recent Trends in Creatinine Assays in Korea: Long-Term Accuracy-Based Proficiency Testing Survey Data by the Korean Association of External Quality Assessment Service (2011-2019)

Background

Accurate serum creatinine (Cr) concentration measurement is essential for evaluating kidney function. In 2011, the Korean Association of External Quality Assessment Service (KEQAS) launched an accuracy-based Cr proficiency testing (ABCr PT) survey. We analyzed long-term data of the KEQAS ABCr PT survey collected between 2011 and 2019 to assess recent trends in Cr assays in Korea.

Methods

The ABCr PT survey including three commutable fresh-frozen serum samples was performed twice a year. The target Cr concentration was assigned using isotope-dilution mass spectrometry. We analyzed data obtained from the participating laboratories, calculated the yearly bias, and evaluated bias trends for the major reagents and instruments. Outliers were excluded from all analysis.

Results

The mean percentage bias based on the total data of all participating laboratories was 10.8% in the 2011-A survey and 0.2% in 2019-B survey. Bias for the major reagents and instruments differed depending on the manufacturer. Enzymatic assays generally showed desirable bias ranging from –3.9% to 3.2% at all Cr concentrations and lower interlaboratory variability than non-enzymatic assays (enzymatic vs. non-enzymatic, 3.3%–7.2% vs. 6.3%–9.1%).

Conclusions

Although the mean percentage bias of Cr assays tends to decrease over time, it is necessary to continuously strive to improve Cr assay accuracy, especially at low concentrations.

Cystatin C predicts long term mortality better than creatinine in a nationwide study of intensive care patients

Decreased glomerular filtration rate (GFR) is linked to poor survival. The predictive value of creatinine estimated GFR (eGFR) and cystatin C eGFR in critically ill patients may differ substantially, but has been less studied. This study compares long-term mortality risk prediction by eGFR using a creatinine equation (CKD-EPI), a cystatin C equation (CAPA) and a combined creatinine/cystatin C equation (CKD-EPI), in 22,488 patients treated in intensive care at three University Hospitals in Sweden, between 2004 and 2015. Patients were analysed for both creatinine and cystatin C on the same blood sample tube at admission, using accredited laboratory methods. During follow-up (median 5.1 years) 8401 (37%) patients died. Reduced eGFR was significantly associated with death by all eGFR-equations in Cox regression models. However, patients reclassified to a lower GFR-category by using the cystatin C-based equation, as compared to the creatinine-based equation, had significantly higher mortality risk compared to the referent patients not reclassified. The cystatin C equation increased C-statistics for death prediction (p < 0.001 vs. creatinine, p = 0.013 vs. combined equation). In conclusion, this data favours the sole cystatin C equation rather than the creatinine or combined equations when estimating GFR for risk prediction purposes in critically ill patients.

Plasma levels of osteopontin from birth to adulthood

AIM

Osteopontin (OPN) has been investigated as a biomarker for cancer and nonmalignant diseases during the last decades. Data about OPN as a potential biomarker in childhood diseases are still sparse, and reference values are not available in children. We aimed to establish reference values for children from birth to young adulthood and evaluate whether there are age-, gender-, and weight-specific differences.

METHOD

Umbilical cord blood and blood plasma samples of 117 children were collected in the Children's Hospital of Saarland University in Homburg/Saar. OPN levels were measured by ELISA, and statistical analysis was performed using SPSS software.

RESULTS

Neonates, infants, toddlers, young children, adolescents, and adults were divided into the following six age groups: newborns (birth), infancy and toddlers (0-24 months), early childhood (3-6 years), middle childhood (7-11 years), adolescence (12-18 years), and adults (> 18 years). Highest blood OPN levels were found in the group of 0-1 years of age. OPN blood levels declined significantly with age (Spearman r = -0.874; P < 0.001).

CONCLUSION

Our work is the first prospective and systematic study analyzing OPN cord blood and blood plasma levels in children of all ages. It is the first study yielding reference values for different age groups from birth to young adulthood. Our data give insight on how OPN in umbilical cord blood and OPN in blood plasma are physiologically influenced during childhood development and growth with high OPN levels after birth and a constant age-related decline until the age of 14, when OPN levels reach similar values to those measured in adults.

Conversion methods for modified Jaffe reaction assays of serum creatinine

BACKGROUND

Modifications in Jaffe serum creatinine (sCr) assays question the suitability of the results for direct comparison.

METHODS

sCr in adult in-patients was routinely measured either by SRM 909-standardized/noncompensated (method A) or isotope dilution mass spectrometry traceable/compensated method (reference). We converted values by method A into values by the reference using a formula provided by the manufacturer [Beckman Coulter (BC)] and traditional equating methods.

RESULTS

The BC-based conversion and linear equating resulted in underestimated sCr values, whereas equipercentile equating (EE) provided sCr with not significantly different distribution from the reference values. Proportions of patients with renal impairment did not differ between the reference and EE-converted sCr, as opposed to BC-recalculated values. Three percent of patients were classified into better renal function category when applying BC versus EE conversion.

CONCLUSIONS

Equipercentile equation was a more accurate method for recalculation of sCr obtained from different Jaffe reaction assays than the linear equating or the BC linear formula. This study emphasizes the importance of the derivation sample specificity when applying research results to other real-world populations.