Pregnanetriol

Using spectrophotometry, the pregnanetriol test determines urine levels of pregnanetriol, the metabolite of the cortisol precursor 17-hydroxyprogesterone. Pregnanetriol is normally excreted in the urine in minute amounts. However, when cortisol biosynthesis is impaired at the point of 17-hydroxyprogesterone conversion, urinary excretion of pregnanetriol rises significantly.

Elevated urine pregnanetriollevels suggest adrenogenital syndrome. Urine 17-ketosteroids and urine 17-ketogenic steroids may be measured concurrently to assess androgen levels. Elevated androgen levels are characteristic of adrenogenital syndrome (congenital adrenal hyperplasia).

Purpose

• To aid diagnosis of adrenogenital syndrome
• To monitor cortisol replacement

Patient preparation

• Explain to the patient (or to the parents if the patient is a child) that this test evaluates hormonal secretion.
• Inform him that he needn't restrict food or fluids before the test.
• Tell him the test requires collection of urine over a 24-hour period, and teach him the proper collection technique.

Procedure and posttest care

• Collect the patient's urine over a 24­hour period. Use a bottle containing a preservative to keep the specimen at a pH of 4.0 to 4.5.

Precautions

• Refrigerate the specimen or keep it on ice during the collection period.
• Send the specimen to the laboratory as soon as the collection is complete.

Reference values

The normal rate of pregnanetriol excretion ranges as follows.

Males

• ages 0 to 5: < 0.1 mg/24 hours
• ages 6 to 9: < 0.3 mg/24 hours
• ages 10 to 15: 0.2 to 0.6 mg/24 hours
• ages 16 and older: 0.2 to 2 mg/ 24 hours

Females

• ages 0 to 5: < 0.1 mg/24 hours
• ages 6 to 9: < 0.3 mg/24 hours
• ages 10 to 15: 0.1 to 0.6 mg/24 hours
• ages 16 and older: 0 to 1.4 mg/ 24 hours.

Abnormal findings

Elevated urine pregnanetriollevels suggest adrenogenital syndrome: excessive adrenal androgen secretion and resulting virilization. Females with this condition fail to develop normal secondary sex characteristics and show marked masculinization of external genitalia at birth. Males usually appear normal at birth but later develop signs of somatic and sexual precocity.

In monitoring treatment with cortisol replacement, elevated urine pregnanetriol levels indicate insufficient dosage of cortisol. When cortisol replacement adequately inhibits hyper­secretion of corticotropin and subsequent overproduction of 17-hydroxyprogesterone, pregnanetriollevels fall within the normal range.

Interfering factors

• Failure to store the specimen properly during the collection period or to send the completed sample to the laboratory immediately
• Exercise (possible increase)