What Causes The Presence Of RBC In Urine Despite Any Visual Evidence Of Blood?

I m concerned about a recent Urine test I had. I ve had blood in the urine in the past and it s typically gone away within a few months and I ve only had to have a follow-up urine test. Can you provide some insight as to why I might have Occult Blood 1+ with RBC 11-30. I m scared. Thank you! F Specific Gravity 1.018 1.005-1.030 PDLCA F pH 7.0 5.0-7.5 PDLCA F Urine-Color Yellow Yellow PDLCA F Appearance Clear Clear PDLCA F WBC Esterase Negative Negative PDLCA F Protein Negative Negative/Trace PDLCA F Glucose Negative Negative PDLCA F Ketones Negative Negative PDLCA F Occult Blood 1+ A Negative PDLCA F Bilirubin Negative Negative PDLCA F Urobilinogen,Semi-Qn 0.2 0.2-1.0 (mg/dL) PDLCA F Nitrite, Urine Negative Negative PDLCA F Microscopic Examination See below: PDLCA - Microscopic was indicated and was performed. Microscopic Examination PDLCA F Urinalysis Reflex PDLCA - This specimen will not reflex to a Urine Culture. F WBC 0-5 0 - 5 (/hpf) PDLCA F RBC 11-30 A 0 - 2 (/hpf) PDLCA F Epithelial Cells (non renal) None seen 0 - 10 (/hpf) PDLCA Epithelial Cells (renal) PDLCA Casts PDLCA Cast Type PDLCA Crystals PDLCA Crystal Type PDLCA F Mucus Threads Present Not Estab. PDLCA F Bacteria Few None seen/Few PDLCA Yeast PDLCA Trichomonas PDLCA