Method Description

Potassium, Sodium, Chloride:

Ion-selective electrode (ISE) (indirect potentiometry). The ion selective electron (ISE) module indirectly measures the electromotive force (EMF) difference between an ISE and a reference electrode. The EMF of the ISE is dependent on the ion concentration of the sample. The EMF of the reference electrode is constant. An electronic calculation circuit converts EMF of the sample to the ion concentration of the sample.(Package insert: ISE Indirect Na, K, CL for Gen2. Roche Diagnostics; 12/2020)

Bicarbonate:

This is a photometric rate reaction. Bicarbonate (HCO3-) reacts with phosphoenolpyruvate in the presence of phosphoenolpyruvate carboxylase to produce oxaloacetate and phosphate. The oxaloacetate produced is coupled with nicotinamide adenine dinucleotide (NADH) in the presence of malate dehydrogenase to produce malate and NAD+. The consumption of NADH causes a decrease in absorbance and is monitored in the UV range of 320 nm to 400 nm. The rate of change is directly proportional to the concentration of bicarbonate.(Package insert: Bicarbonate reagent. Roche Diagnostics; 04/2019)

Anion Gap:

This is a calculated result. The following equation is used to calculate the anion gap (A gap):

A gap = Na - (Cl + HCO3-)

Blood Urea Nitrogen (BUN):

This is a kinetic UV assay where urease cleaves urea to form ammonia and carbon dioxide. The ammonia formed then reacts with alpha-ketoglutarate and NADH in the presence of urease/glutamate dehydrogenase to yield glutamate and NAD+. The decrease in absorbance, due to the consumption of NADH, is measured kinetically and is proportional to the amount of urea in the sample.(Package insert: Urea/BUN reagent. Roche Diagnostics; 12/2019)

Creatinine:

This enzymatic method is based on the conversion of creatinine with the aid of creatininase, creatinase, and sarcosine oxidase to glycine, formaldehyde, and hydrogen peroxide. Catalyzed by peroxidase, the liberated hydrogen peroxide reacts with 4-aminophenazone and HTIB (hydroxy[tosyloxy]iodobenzene) to form a quinone imine chromogen. The color intensity of the quinone imine chromogen formed is directly proportional to the creatinine concentration in the reaction mixture.(Package insert: Creatinine. Roche Diagnostics; 02/2019)

Estimated Glomerular Filtration Rate:

Estimated GFR (eGFR) is calculated using the 2021 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation:

Females:

If creatinine ≤0.7 mg/dL: 142 x (Scr/0.7)(-0.241) x 0.9938age x 1.012

If creatinine >0.7 mg/dL: 142 x (Scr/0.7)(-1.200) x 0.9938age x 1.012

Males:

If creatinine ≤0.9 mg/dL: 142 x (Scr/0.9)(-0.302) x 0.9938age

If creatinine >0.9 mg/dL: 142 x (Scr/0.9)(-1.200) x 0.9938age

Values are reported for calculated glomerular filtration rate (GFR) estimates between 15-90 mL/min/1.73 m(4). Estimated GFR values outside of this range are reported as "<15 mL/min/1.73 m(2)" or ">90 mL/min/1.73 m(4)" and not as an exact number.

Calcium:

Calcium ions react with NM-BAPTA (5-nitro-5'-methyl-1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid)under alkaline conditions to form a complex. This complex reacts in the second step with EDTA. The change in absorbance is directly proportional to the calcium concentration and is measured photometrically.(Package insert: Calcium Gen.2 reagent. Roche Diagnostics; 07/2019)

Glucose:

Glucose in the serum, in the presence of hexokinase, is converted to glucose-6-phosphate (G6P). In the presence of nicotinamide adenine dinucleotide phosphate (NADP+), glucose-6-phosphate dehydrogenase oxidizes G6P to gluconate-6-phosphate and NADPH. The rate of NADPH formation is directly proportional to glucose concentration in the serum and is measured photometrically.(Package insert: Glucose HK Gen.3 Reagent. Roche Diagnostics; 11/2021)

Albumin:

The dye, bromcresol green (BCG), is added to serum in an acid buffer. The color intensity of the blue-green albumin-BCG complex is directly proportional to the albumin concentration and is determined photometrically.(Package insert: Albumin Gen.2 reagent. Roche Diagnostics; 02/2022)

Phosphorus (Inorganic):

Inorganic phosphate forms an ammonium phosphomolybdate complex with ammonium molybdate in the presence of sulfuric acid. The concentration of phosphomolybdate formed is directly proportional to the inorganic phosphate concentration and is measures photometrically.(Package insert: Phosphate (Inorganic) ver 2. Roche Diagnostics; V11.0, 07/2019)