Combined eGFR

Physiological Role

The kidneys continuously filter blood plasma to eliminate metabolic waste, regulate fluid balance, and maintain electrolyte concentrations. This filtration takes place in the glomeruli, tiny vascular structures located in the renal cortex. Each kidney contains roughly one million of them.

The glomerular filtration rate measures the speed at which plasma passes through these glomeruli. A healthy adult filters approximately 180 liters of plasma per day. From this volume, the renal tubules reabsorb nearly all water and useful nutrients, allowing only one to two liters of urine through.

With age, the number of functional nephrons (the kidney's filtration units, each composed of a glomerulus and a tubule) decreases gradually. This loss is estimated at roughly 1 mL/min/1.73 m2 per year after age 40. Combined eGFR quantifies this evolution and distinguishes normal physiological decline from accelerated functional impairment.

Reference Ranges

Depending on the biomarker, Singular ranges are based on a synthesis of nutritional or clinical reference points and longevity research. They do not replace your laboratory's reference values or your healthcare professional's advice.

Biological Significance

A combined eGFR in the optimal zone indicates that the kidneys are filtering plasma efficiently. Filtration capacity is preserved, metabolic waste is cleared, and internal balance is maintained.

Values in the low zone signal a slowdown in filtration. Common causes include aging, chronic hypertension, diabetes, and certain conditions affecting kidney function. A single value in this zone is not conclusive. The trend across multiple successive measurements is more informative than a one-time result.

Values in the very low zone reflect significant impairment of glomerular filtration. Regular monitoring confirms the trend and helps guide appropriate follow-up.

Combined eGFR reading gains precision when compared with creatinine-only and cystatin C-only eGFR estimates. A gap between these two estimates may reveal bias linked to body composition, particularly in muscular individuals.

Influencing Factors

Age. eGFR naturally declines with aging. After 40, the average loss is roughly 1 mL/min/1.73 m2 per year. This evolution is physiological.

Hydration. Even mild dehydration can temporarily lower eGFR by reducing blood volume reaching the kidneys. Stable hydration before the blood draw ensures a representative result.

Diet. High protein intake transiently increases eGFR by stimulating renal perfusion. A very restrictive diet or prolonged fasting can decrease it.

Blood pressure. Chronic hypertension progressively damages the glomeruli. Maintaining blood pressure within normal ranges is a well-documented lever for kidney preservation.

Body composition. Creatinine is a byproduct of muscle metabolism. Individuals with high muscle mass may display elevated creatinine without kidney impairment. Combined eGFR compensates for this bias through cystatin C.

Physical activity. Intense exercise can transiently elevate creatinine. Cystatin C is far less sensitive to exertion: after a marathon it rises by 21% on average, against 41% for creatinine. Combined eGFR attenuates these fluctuations.

Medications. Certain anti-inflammatory drugs, ACE inhibitors, and diuretics can alter eGFR.

In the Singular Formula

Combined eGFR is recalculated server-side from creatinine, cystatin C, biological sex and year of birth, then categorized like a measured biomarker.

When it is categorized as very low, the renal precaution rule removes creatine, glucosamine sulfate, iodine, taurine and magnesium, and caps vitamin C at 250 mg. The same precaution applies independently when impaired kidney function is reported in the health profile.

When it is categorized as low, it triggers only hydration and lifestyle advice. Neither trigger adds or changes a condition in the health profile.

Scientific Studies

Frequently Asked Questions