Question 1

can an abdominal ct scan with and without contrast detect micronodular adrenal adenomas? what's the false negative possibilities?

Accepted Answer

Adrenal adenomas: With most gland problems, first figure out if the hormones are elevated.  If so, THEN go looking for the tumor.  This is because all glands form nodules, but these nodules often have no consequence.  If you have a hormone elevation (Cushings, pheo, aldosteronoma) and the source is the adrenal, the CT will almost always find it. But this is complicated.  See your Endocrinologist.

Question 2

male w/ 1/12 urethritis symptoms. since then i have had 2 x negative sti tests with ct and ultrasound also -ve. symptoms ongoing. 1st uc was taken 1 hour post urination and 2nd whilst taking trimethaprim. chance of 2 x false negative results?

Accepted Answer

: More info needed. What symptoms? Why CT and ultrasound? They cannot diagnose urethritis -- maybe actually a prostate problem? Trimethoprim isn't available in the US; maybe sulfa-trimethoprim (Bactrim)? That antibiotic doesn't treat urethritis. Have you also been tested for UTI bacteria? Or for Mycoplasma genitalium? Ask a clearer question and maybe we can help. But it seems no urethritis at all.

Question 3

what exactly does it mean to have a false-negative result in a cat scan?

Accepted Answer

It means: That the ct scan was negative for pertinent findings while the condition or disease of the patient was demonstrated to be in existence at the time of the scan.

Question 4

what are the chances of false negative mris and cat scans? what are the odds that an mri and a cat scan would both show no cancer when there really is cancer present? what about the opposite, where they would both should cancer when there really is none?

Accepted Answer

This : This depends widely on what part of the body is being imaged, what type of cancer is present (or hopefully not present), how large the cancer is, and what type of MRI or ct is performed.  If the proper imaging study is performed to evaluate for a specifically suspected cancer then the percentage of cancers that are discovered is very high and the "false" cancers detected is quite low. The best imaging study must be determined on a case-by-case basis by yourself, your primary care provider, and often a radiologist. 
I strongly advise against having any imaging study performed if you have no symptoms or only vague, nonspecific symptoms. Not only does this often lead to unnecessary cost, but also greatly increases the chances of falsely finding a "cancer". This in turn can lead to additional expensive testing and a lot of unnecessary emotional distress.

Question 5

what causes false negative hpt? is it common?

Accepted Answer

Does happen: Some things that can cause a false negative HPT: Taking the test too early; Checking the results too soon (you have to read instructions and set a timer); Drinking a lot of water can dilute your urine and give you a false negative (first am urine is most concentrated).  A pregnancy that isn't doing well such as an ectopic pregnancy sometimes doesn't make enough hormone to turn a test positive.

Question 6

tetrahydrocanabinol what causes for false negative and false positive?

Accepted Answer

Great question: I think dilute urine is the most likely source for false negatives.   I am not familiar with other substances outside of the cannabinoid class of compounds (some of the newer synthetics?) that will react with standard immunoassays.   If one is concerned, however, about a false positive there is confirmatory testing that can determine for sure whether it was a false positive or not.

Question 7

can antibiotics cause false negative uti test?

Accepted Answer

Yes: If an antibiotic is taken before submitting the urine specimen, the urine culture is likely to show no growth (false negative) and urinalysis in general have a high rate of false positives and false negatives.

Question 8

what could cause a false negative on a drug test for barbiturates?

Accepted Answer

The typical reason: is that the urine metabolite was below the "cutoff" levels for the screening which would not then be subjected to confirmation.  It is not that barbituates were not in the sample, but that they were below the "positive" quantitative level for confirmation.  Barbiturates are not on federally mandated testing so the cutoff level is arbitrarily assigned.

Question 9

is it possible to have a false negative hpt at 7 1/2 weeks pregnant ?

Accepted Answer

No: As I mentioned earlier, if the test is done correctly, hpt is accurate and would be positive at 7 weeks of pregnancy. If you have any doubt, get a blood test for HCG level and that would be conclusive.
Wish you good health!

Question 10

is it possible to get a false negative when you are 6 weeks pregnant?

Accepted Answer

No: Unless the test kit is defective or you don't follow directions, no way will a pregnancy test be not reliable at 6 weeks. Believe what the test says.

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Doctor answers about:

Ct false negative

A member asked:

Can an abdominal ct scan with and without contrast detect micronodular adrenal adenomas? what's the false negative possibilities?

A member asked:

Male w/ 1/12 urethritis symptoms. since then i have had 2 x negative sti tests with ct and ultrasound also -ve. symptoms ongoing. 1st uc was taken 1 hour post urination and 2nd whilst taking trimethaprim. chance of 2 x false negative results?

A member asked:

What exactly does it mean to have a false-negative result in a cat scan?

A member asked:

What are the chances of false negative mris and cat scans? what are the odds that an mri and a cat scan would both show no cancer when there really is cancer present? what about the opposite, where they would both should cancer when there really is none?

A member asked:

What causes false negative hpt? is it common?

A member asked:

Tetrahydrocanabinol what causes for false negative and false positive?

A member asked:

Can antibiotics cause false negative uti test?

A member asked:

What could cause a false negative on a drug test for barbiturates?

A member asked:

Is it possible to have a false negative hpt at 7 1/2 weeks pregnant ?

A member asked:

Is it possible to get a false negative when you are 6 weeks pregnant?

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