Reliable quantification of renal function from frozen blood samples

Area of Science:

• Gerontology
• Nephrology
• Neurology

Background:

• Renal function influences Alzheimer's disease (AD) blood biomarker levels independently of AD pathology.
• Quantifying estimated glomerular filtration rate (eGFR) from frozen samples could address unaccounted renal function in AD biomarker studies.
• The reliability of eGFR assessment from long-term frozen blood samples was previously unestablished.

Purpose of the Study:

• To determine the validity of eGFR evaluation from long-term frozen serum and plasma blood samples.
• To assess the agreement between eGFR measurements from point-of-care whole blood (POC-WB) and frozen blood samples.

Main Methods:

• Adults aged 50-85 with vascular risk factors were recruited.
• Creatinine was assessed using iSTAT (Abbott) in POC-WB and frozen serum/plasma samples.
• eGFR was calculated using the 2021 CKD-EPI equation; agreement was assessed using Cohen's kappa.

Main Results:

• 134 participants had POC-WB eGFR data; 23.1% had chronic kidney disease.
• Frozen serum and plasma samples showed strong agreement with POC-WB for eGFR (Kw=0.90-0.95, P<0.001).
• Pre-analytical factors minimally impacted eGFR differences between POC-WB and frozen samples.

Conclusions:

• Renal function assessment from frozen blood samples is highly consistent with POC-WB measurements.
• This method is relevant for interpreting AD blood biomarkers in aging and vascular populations with potential renal impairment.