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What time of Day to Get Blood Tests
Feb 12, 2005

Dr Sherer

Do you generally have your patients get tests at a particular time of day or does it vary?

I ask this question because many books on HIV suggest that CD4 counts are naturally as much as 200 points higher in the afternoon than in the morning. Two doctors on this site have given different answers about this and apparently there are also studies that show that counts can be higher in the morning.

It seems to me that until a definitive study is done to answer this question all studies and comparisisons relying on CD4 as an indicator are unreliable, except that if ones cD4 count keeps falling over time this is a bad thing and counts below 200 are a bad thing.

But if a CD4 count can be 200 higher in the evening than in the morning doesnt the same count have different health implications depending on when in the day it was taken?

Should studies report when counts were done?

Response from Dr. Sherer

Most HIV clinicians are aware of this issue, but this does not mean that the CD4 cell counts for a given patient are not reliable. Usually, patients are seen at the same time of day (morning or afternoon), and usually have their lab tests drawn at the same time of day in the same lab. As you suggest, the physician is responsible for ensuring that these statements are true for a given patient, and for being aware of exceptions to these rules.

The most recent CD4 cell count is the strongest predictor of a patient's prognosis, so the issues of relying on both a single CD4 cell count number and trends over time are extremely important, as you suggest.

Finally, when an 'outlyer' value of CD4 cell count is observed by a physician, the usual practice is to repeat it, and to explore possible reasons for the discrepancy, one of which might be the time of day. If you have concerns regarding these issues in your own care, I urge you to discuss them with your doctor.

Questioning Doctor's Treatment
CD4 count 299.....should i start it now?

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