Measurement of Renal Function
A simple means of estimating renal function is to measure pH, blood urea nitrogen, creatinine, and basic electrolytes (including sodium, potassium, chloride, and bicarbonate). As the kidney is the most important organ in controlling these values, any derangement in these values could suggest renal impairment.
There are several more formal tests and ratios involved in estimating renal function:
| Measurement | Calculation | Details |
| renal plasma flow | Volume of blood plasma delivered to the kidney per unit time. PAH clearance is a renal analysis method used to provide an estimate. Approximately 625 ml/min. | |
| renal blood flow | (HCT is hematocrit) | Volume of blood delivered to the kidney per unit time. In humans, the kidneys together receive roughly 20% of cardiac output, amounting to 1 L/min in a 70-kg adult male. |
| glomerular filtration rate | (estimation using creatinine clearance) | Volume of fluid filtered from the renal glomerular capillaries into the Bowman's capsule per unit time. Estimated using inulin. Usually a creatinine clearance test is performed but other markers, such as the plant polysaccharide inulin or radiolabelled EDTA, may be used as well. |
| filtration fraction | Measures portion of renal plasma that is filtered. | |
| anion gap | AG = − ( + ) | Cations minus anions. Excludes K+ (usually), Ca2+, H2PO4−. Aids in the differential diagnosis of metabolic acidosis |
| Clearance (other than water) | where U = concentration, V =urine volume / time, U*V = urinary excretion, and P = plasma concentration | Rate of removal |
| free water clearance | or | The volume of blood plasma that is cleared of solute-free water per unit time. |
| Net acid excretion | Net amount of acid excreted in the urine per unit time |
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Read more about this topic: Renal Physiology
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