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Different labs use different formulas and procedures to calculate the anion gap, so the reference range (or "normal" range) from one lab isn't directly interchangeable with the range from another. The reference range provided by the particular lab that performed the testing should always be used to interpret the results. [3]
Urine NH 4 + is difficult to measure directly, but its excretion is usually accompanied by the anion chloride. A negative urine anion gap can be used as evidence of increased NH 4 + excretion. In a metabolic acidosis without a serum anion gap: A positive urine anion gap suggests a low urinary NH 4 + (e.g. renal tubular acidosis).
Reference ranges for urine tests are described below: Measurement Lower limit Upper limit Unit Urinary specific gravity: 1.003 [1] [2] 1.030 [1] [2] g/mL Urobilinogen:
The anion gap is calculated by subtracting the sum of the serum concentrations of major anions, chloride and bicarbonate, from the serum concentration of the major cation, sodium. (The serum potassium concentration may be added to the calculation, but this merely changes the normal reference range for what is considered a normal anion gap)
The serum anion gap is useful for determining whether a base deficit is caused by addition of acid or loss of bicarbonate. Base deficit with elevated anion gap indicates addition of acid (e.g., ketoacidosis). Base deficit with normal anion gap indicates loss of bicarbonate (e.g., diarrhea).
Urine electrolyte levels can be measured in a medical laboratory for diagnostic purposes. The urine concentrations of sodium, chlorine and potassium may be used to investigate conditions such as abnormal blood electrolyte levels, acute kidney injury, metabolic alkalosis and hypovolemia.
The standard definition of a reference range for a particular measurement is defined as the interval between which 95% of values of a reference population fall into, in such a way that 2.5% of the time a value will be less than the lower limit of this interval, and 2.5% of the time it will be larger than the upper limit of this interval, whatever the distribution of these values.
The normal range of GFR, adjusted for body surface area, is 100–130 average 125 (mL/min)/(1.73 m 2) in men and 90–120 (mL/min)/(1.73 m 2) in women younger than the age of 40. In children, GFR measured by inulin clearance is 110 (mL/min)/(1.73 m 2 ) until 2 years of age in both sexes, and then it progressively decreases.