DEAR DR. DONOHUE: What is the difference between the T-score and the Z-score on osteoporosis tests? – M.S.

ANSWER: The standard test to screen for osteoporosis is the DEXA (dual-energy X-ray absorptiometry) test. It discloses the strength of bones and how great is their calcium content.

The results of the test are given as T-scores or Z-scores. A T-score compares a patient’s bone strength and calcium content with the bone strength of a healthy young adult. A T-score of -2.5 or less indicates osteoporosis. A score of -1 to -2.5 is osteopenia – not osteoporosis, but on the way to becoming osteoporosis. Most decisions about treatment are made on the basis of a T-score.

A Z-score is a comparison between a patient’s bone strength and calcium content and the bone strength and calcium content of a person of the same sex and age. A Z-score of less than -2 indicates that a person is not absorbing enough calcium to keep bones healthy. The problem might be overactive parathyroid glands or one of the many malabsorption syndromes that block calcium’s passage across the digestive tract and into the blood. Z-scores provide additional information but do not define osteoporosis. Often, they are not reported.

DEAR DR. DONOHUE: On my last doctor visit, I had a blood test, and my blood sugar was 145 (8.0). The doctor said I was getting diabetes. I bought some test strips to watch my blood sugar. I test in the morning before having any food and get a reading of over 180 (9.9). At 5 p.m., before dinner, the reading is around 120 (6.6). Why the big difference from morning to evening? How do I know if I have diabetes? – N.H.

ANSWER: Most doctors diagnose diabetes with a fasting plasma glucose (blood sugar). “Fasting” means not having any calories during the eight hours before the blood was drawn. Normal plasma glucose should be less than 100 mg/dL (5.6 mmol/L). A reading of 126 (7) or higher indicates diabetes. Values between those two numbers are called “prediabetes.” A second test, done on a different day, should be used to confirm the reliability of the first test. Were you fasting for eight hours before your blood was drawn?

When blood sugar remains high for days and days, people urinate large quantities, are extremely thirsty and have huge appetites but lose weight.

You can’t be left to yourself to make a diagnosis of diabetes. You have to have the doctor do that for you. It’s the reason why doctors are paid; it’s their job. Test strips are not accurate enough to confirm a diabetes diagnosis.

The differences in blood sugar should not surprise you. Sugar values fluctuate depending on when a person last ate and on what was eaten. During the day, when you are up and about, sugar is burned, and that could account for your evening sugar drop.

Diabetes cases have reached epidemic proportions. The booklet on diabetes explains the different kinds and how they’re treated. Readers can order a copy by writing: Dr. Donohue – No. 402, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com

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