Périchon, Régis

AbstractBACKGROUNDClinical practice guidelines recommend estimation of glomerular filtration rate (eGFR) using validated equations based on serum creatinine (eGFRcr), cystatin C (eGFRcys), or both (eGFRcr-cys). However, when compared with the measured GFR (mGFR), only eGFRcr-cys meets recommended performance standards. Our goal was to develop a more accurate eGFR method using a panel of metabolites without creatinine, cystatin C, or demographic variables.METHODSAn ultra-performance liquid chromatography–tandem mass spectrometry assay for acetylthreonine, phenylacetylglutamine, pseudouridine, and tryptophan was developed, and a 20-day, multiinstrument analytical validation was conducted. The assay was tested in 2424 participants with mGFR data from 4 independent research studies. A new GFR equation (eGFRmet) was developed in a random subset (n = 1615) and evaluated in the remaining participants (n = 809). Performance was assessed as the frequency of large errors [estimates that differed from mGFR by at least 30% (1 − P30); goal <10%].RESULTSThe assay had a mean imprecision (≤10% intraassay, ≤6.9% interassay), linearity over the quantitative range (r2 > 0.98), and analyte recovery (98.5%–113%). There was no carryover, no interferences observed, and analyte stability was established. In addition, 1 − P30 in the validation set for eGFRmet (10.0%) was more accurate than eGFRcr (13.1%) and eGFRcys (12.0%) but not eGFRcr-cys (8.7%). Combining metabolites, creatinine, cystatin C, and demographics led to the most accurate equation (7.0%). Neither equation had substantial variation among population subgroups.CONCLUSIONSThe new eGFRmet equation could serve as a confirmatory test for GFR estimation.

Background— Multiple B-type natriuretic peptide (BNP) fragments circulate in patients with heart failure (HF) but the types and relative quantities, particularly in relation to bioactive BNP 1-32, remain poorly defined. The purpose of the study was to relate clinically available BNP values with quantitative information on the concentration of pre-secretion and post-processed fragments of BNP detected by mass spectrometry. Methods and Results— Seventy Class I–IV patients were prospectively enrolled with blood drawn into tubes containing a preservative to protect against BNP degradation. Samples were analyzed by quantitative mass spectrometry (MS) immunoassay for intact BNP 1-32 and its fragments. Clinical BNP 1-2 was measured by standard clinical laboratory methods. ProBNP 1-108, corin, and clinically measured BNP levels were elevated, but MS BNP 1-32 levels were low and differed from clinical BNP ( P =0.01). Intact MS BNP 1-32 correlated modestly with clinical BNP ( r =0.46, P <0.001). MS BNP fragments 3-32, 4-32, and 5-32 demonstrated the best associations with clinical BNP; fragment 5-32 with a correlation coefficient of r =0.81 ( P <0.001). Conclusions— ProBNP 1-108 is measured by clinical BNP assays and contributes to the cumulative results of the BNP assay. However, the observation that clinically measured BNP correlates best with MS degradation fragments and relatively poorly with MS BNP 1-32 suggests that a significant component of circulating clinical BNP is composed of such fragments that are known to demonstrate little biological activity. There appear to be multiple pathways involved in the dysregulation of proBNP in HF, and both the processing of proBNP and the downstream degradation to BNP 1-32 appear to be critical.