The purpose of this study is to determine whether laboratory storage of samples affects the amount of lactate over 3 years.

Lactate is a natural substance normally present in the body. Lactate levels can go up for many different reasons, including treatment with nucleotide reverse transcriptase inhibitor drugs. This study will help researchers know if stored blood samples can be used to test lactate levels.

Lactic acidosis syndrome is a complication of therapy with nucleoside reverse transcriptase inhibitor (NRTI) drugs. Measurement of lactate levels is important in clinical trials of antiretroviral treatments. The preferred collection method for determining plasma lactate is with NaF/KOx tubes, while a number of ACTG studies have stored blood in ethylenediaminetetraacetic acid (EDTA) tubes. This study will analyze lactate in samples collected and stored in NaF/KOx and EDTA tubes to investigate the reliability of lactate concentrations over time.

Pre- and post-exercise blood samples are drawn from participants into NaF/KOx and EDTA tubes and a portion is tested for lactate levels immediately. The remaining portions are frozen and tested at 1, 3, 6, 12, 18, 24, and 36 months.

Inclusion Criteria

Participants may be eligible for this study if they:

• Are at least 18 years old.
• Have sufficient forearm veins.

Exclusion Criteria

Participants will not be eligible for this study if they:

• Have a physical disability that prevents forearm exercise.
• Have any known medical reason, such as anemia, for not having 82 ml of blood drawn.