Untitled Flashcard Set

Category

Formula

Normal/Constant

Purpose

BUN Assay

BUN = (A Unknown ÷ A Standard) × 30

30 mg/dL Standard

Determine BUN concentration

Creatinine Assay

Creatinine = (ΔA Unknown ÷ ΔA Standard) × 5

5 mg/dL Standard

Determine creatinine concentration

Urea Conversion

Urea = BUN × 2.14

2.14 conversion factor

Convert BUN to Urea

BUN Conversion

BUN = Urea ÷ 2.14

2.14 conversion factor

Convert Urea to BUN

BUN/Creatinine Ratio

BUN ÷ Creatinine

10–20 : 1

Evaluate renal perfusion/function

Calculation

Formula

Normal Range

Clinical Use

Anion Gap (with K)

Na + K − (Cl + HCO3)

10–20 mmol/L

Metabolic acidosis evaluation

Anion Gap (without K)

Na − (Cl + HCO3)

7–16 mmol/L

Most common AG calculation

Calculated Osmolality

2(Na) + Glucose/20 + BUN/3

275–295 mOsm/kg

Estimate serum osmolality

Alternative Osmolality

1.86(Na)+Glucose/18+BUN/2.8+9

275–295 mOsm/kg

More precise estimate

Osmolal Gap

Measured − Calculated Osmolality

<15 mOsm/kg

Detect unmeasured osmoles

Analyte

Reference Range

Units

Sodium (Na)

135–145

mmol/L

Potassium (K)

3.5–5.0

mmol/L

Chloride (Cl)

96–106

mmol/L

Bicarbonate (HCO3)

22–29

mmol/L

Calcium (Ca)

8.5–10.5

mg/dL

Magnesium (Mg)

1.5–2.6

mg/dL

Phosphorus (P)

2.5–4.5

mg/dL

Analyte

Reference Range

Key Point

BUN

8–25 mg/dL

Protein metabolism waste

Creatinine Female

0.6–1.1 mg/dL

Reflects GFR

Creatinine Male

0.7–1.3 mg/dL

Reflects GFR

Creatinine Clearance Female

95 ± 20 mL/min

Kidney filtration

Creatinine Clearance Male

105 ± 20 mL/min

Kidney filtration

Uric Acid

2.6–7.2 mg/dL

Purine metabolism

Ammonia

19–60 mg/dL

Liver & nitrogen metabolism