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Is it Ok to do blood test while taking antibiotics Keflex?

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Answered by

General & Family Physician
Practicing since : 2009
Answered : 664 Questions
I am on keflex 500 mg 4x day for last 6 days for chest infection but had partially ruptured ovarian cyst few days ago and my gyno ordered CBC with diff today to see if cyst is causing bleeding like anemia or infection but I forgot to tell her I am on keflex til end of day tomorrow.
Should I wait til after I finish the antibiotics to take the blood test or does it not matter and I can take the test tomorrow even while on the keflex?
Posted Tue, 26 Aug 2014 in Medicines and Side Effects
Answered by Dr. Yogesh D 18 minutes later
Brief Answer:
It is okay to get the tests done while on antibiot

Detailed Answer:

Thanks for posting your query.

CBC will not be affected much while you are antibiotics, except the WBC counts and differential counts of WBCs all other parameters would remain unchanged if you are on antibiotics, and WBC counts will reduce to normal levels if the infection is controlled with antibiotics, so there is nothing to be worried about. You can safely go ahead and get the test done now.

Hope this answers your query.

Above answer was peer-reviewed by
Follow-up: Is it Ok to do blood test while taking antibiotics Keflex? 4 minutes later
I am worried though that if I do tomorrow and white blood cells look fine because I am on antibiotic, next day when I am off antibiotic they may go up but we wouldnt realize so incase there is an infection from the partially ruptured cyst, how long should I wait after stopping antibiotics to get realistic WBC? 24 hours, 48 hours?
Answered by Dr. Yogesh D 9 minutes later
Brief Answer:
If there is an infection then abs will take care

Detailed Answer:
Dear madam,

Do not worry, the antibiotics you are currently on will take care of the infection if it is there, and doing the CBC now will also show if the antibiotic is working. (You would have to keep in mind that WBCs can be raised even if you don't have an infection due to ruptured cyst because a ruptured cyst can cause a bit of inflammation and inflammation can elevate the WBC numbers).

In my opinion, getting the CBC done now will benefit you, and you can get it repeated a day or two after you complete the antibiotic course to see how things are going.

CBC is not a specific test for infections, blood culture is, so if you are worried about infection, you should get a blood culture done, but since you are already on antibiotics, blood culture may not show.

Get the CBC done, wait for two days after the completion of the antibiotics and get the CBC repeated.

Hope this clears things up.

Kind regards.
Above answer was peer-reviewed by
Follow-up: Is it Ok to do blood test while taking antibiotics Keflex? 23 minutes later
Ok so if I do test tomorrow, stop keflex tomorrow night since its my last night, and results comes back in couple of days WBC is fine, go back few days later retake test and wbc goes up, do i have to go on another antibiotic or not necessarily? Also, how long would I wait for follow up test (how long after I stop keflex, 24 hours, 48 hours, ?) Is it ok to stop Keflex you think? I was given it for chest infection which was day after cyst partially ruptured. Do you think I need to stay on it longer since I still have pain from cyst partially rupturing or do you not even necessarily need to be on antibiotics for a ruptured cyst?
Answered by Dr. Yogesh D 17 minutes later
Brief Answer:
If it is last day, finish the course and then test

Detailed Answer:
Hello again,

You have one more day to go for completing the antibiotics, I guess you can wait it over and get the test done as it will not make much of a difference.

You can wait for 48 hours for a follow up test.

Antibiotics may not be necessary if you do not have any clinical sign of infection, as mentioned earlier, WBC counts may be raised in conditions other than infection, and elevated WBCs do not always mean infection.

It is not ok to stop Keflex now, finish the course so that chest infection is cleared.

You do not need to take antibiotics for a ruptured cyst, internal cysts are sterile so it is pointless to take antibiotics for a ruptured cyst, however, if you are having an infection elsewhere at the time of rupture of the cyst, a prophylactic antibiotic course will be recommended, in your case that job would have been done by keflex you are taking for chest infection.

So, please complete the antibiotic course, get the CBC done a day after you complete the antibiotics, and repeat CBC after 48 hours after the first test to see how you are doing.

A single CBC will not give much information regarding infections, hence a repeat test is advisable.

If the second CBC shows an increasing trend in WBCs, you will require another course of specific antibiotics (which will be chosen based on the culture and sensitivity test).

I hope this will help clear your doubts further.

Warm regards.
Above answer was peer-reviewed by
Follow-up: Is it Ok to do blood test while taking antibiotics Keflex? 2 hours later
The chest infection is all cleared up but I will finish the antibiotic.
Just curious, why do you think my gyno ordered a CBC with diff for my ruptured cyst condition?
Answered by Dr. Yogesh D 21 hours later
Brief Answer:
WBC counts can be raised in any inflammation.

Detailed Answer:
Hello again,

Thanks for the follow up.

As I have mentioned in my earlier responses, WBCs can be raised in any inflammation and elevated WBC counts are indicator of inflammation in general, be it due to infection or tissue injury due to any other cause. Apart from this, CBC will also include hemoglobin level estimation, RBC counts and platelet counts which can give information about blood loss if it is severe.

So, your gynecologist must have ordered CBC to look for signs of inflammation as well as hemoglobin levels.

Hope this answers your question.

Wishing you speedy recovery.

Warm regards.
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