General laboratory tests will be performed in the clinical chemistry laboratories of study sites including CBCs, lymphocyte subsets (CD4, CD8), HIV viral load, renal and liver function tests. Sera for specialized biochemistries (PTH, vitamin D metabolites, OC, BSAP, NTx) is aliquoted, frozen immediately after collection, and transferred to SLRHC where they will be stored at -70 degrees. The frozen samples will be analyzed in the Core laboratory of the Irving Center for Clinical Research at Columbia University. All samples from individual subjects will be analyzed in batches in the same assay to reduce inter-assay variability. All of the planned assays are currently in place in the Core Laboratory.