Understand Blood Test Results
Learn what common blood test markers mean, why results may be high or low, and how to understand your lab report in plain English.
Educational information only. LabTestly does not diagnose or replace medical advice.
Why high and low flags need context
A single “high” or “low” result does not tell the whole story. Lab results are usually interpreted with related markers, reference ranges, previous results, symptoms, and medical history. A flagged value is a question to investigate — not an answer.
Popular result-based guides
- High ALT on a blood testWhat it can mean · ALT
- High AST on a blood testWhat it can mean · AST
- High Creatinine on a blood testWhat it can mean · Creatinine
- High Glucose on a blood testWhat it can mean · Glucose
- High TSH on a blood testWhat it can mean · TSH
- Low Ferritin on a blood testWhat it can mean · Ferritin
- Low Hemoglobin on a blood testWhat it can mean · Hemoglobin
- High WBC on a blood testWhat it can mean · WBC
- High Platelets on a blood testWhat it can mean · Platelets
- High CRP on a blood testWhat it can mean · CRP
What do H, L, and arrows mean on a lab report?
Many lab reports mark results as H for high, L for low, or show arrows (↑ ↓) when a value is outside the lab's reference range. These flags are useful — but they still need context. The same flag can mean very different things depending on related markers and your history.
Upload your PDF to see your flagged results explained together →
Don't guess from one flagged result.
Upload your full lab report PDF and see how your markers fit together in plain English.
Browse markers by category
90+ common blood test markers, grouped the way a clinician reads a lab panel.
Complete Blood Count
Browse all →- Hemoglobin
- WBCWhite Blood Cell Count
- RBCRed Blood Cell Count
- Hematocrit
- MCVMean Corpuscular Volume
- MCHMean Corpuscular Hemoglobin
- MCHCMean Corpuscular Hemoglobin Concentration
- RDWRed Cell Distribution Width
- PlateletsPlatelet Count
- NeutrophilsNeutrophil Count
- LymphocytesLymphocyte Count
- MonocytesMonocyte Count
- EosinophilsEosinophil Count
- BasophilsBasophil Count
- ReticulocytesReticulocyte Count
Liver Function
Browse all →Kidney Function
Browse all →Lipid Panel
Browse all →Glucose & Metabolic
Browse all →Thyroid
Browse all →Electrolytes
Browse all →Vitamins & Minerals
Browse all →Inflammation
Browse all →Hormones
Browse all →- TestosteroneTotal Testosterone
- EstradiolEstradiol (E2)
- CortisolSerum Cortisol
- DHEA-SDehydroepiandrosterone Sulfate
- LHLuteinising Hormone
- FSHFollicle Stimulating Hormone
- ProlactinSerum Prolactin
- Free Testosterone
- SHBGSex Hormone Binding Globulin
- ProgesteroneSerum Progesterone
- IGF-1Insulin-like Growth Factor 1
- GHGrowth Hormone
- 17-OH Progesterone17-Hydroxyprogesterone
- Androstenedione
- AMHAnti-Müllerian Hormone
- PSAProstate-Specific Antigen
- Free PSAFree Prostate-Specific Antigen
- % Free PSAFree PSA Percentage
Frequently asked questions
What is a blood test marker?
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A marker is a single thing measured in your blood — like ALT, glucose, or hemoglobin. Each marker reflects a different aspect of how your body is working. Most lab reports show many markers grouped into panels.
What does “high” mean on a lab result?
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A result is flagged high when it sits above the lab’s reference range. That does not automatically mean something is wrong — ranges are population averages, and many factors (recent meals, exercise, illness, medication, lab method) can push a value temporarily outside the range.
What does “low” mean on a lab result?
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Low means the result is below the lab’s reference range. As with high results, context matters: a single low value is rarely the whole story, and related markers usually help explain whether it is meaningful.
Are reference ranges the same for everyone?
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No. Reference ranges depend on the lab, the equipment used, and often on sex, age, and pregnancy. The range on your specific report is the one to compare your result against — not a range from a different lab or website.
Can LabTestly diagnose me?
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No. LabTestly explains lab markers in plain language so you can understand your report and have better conversations with your clinician. It does not diagnose conditions or replace medical advice.
Can I upload a blood test PDF?
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Yes — upload your lab PDF (or a photo of it) and LabTestly reads the markers, flags out-of-range results, and explains each one. Your first upload is free.
Should I talk to a doctor about abnormal results?
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Yes. Any persistently abnormal result, or any result paired with symptoms, deserves a conversation with a clinician. The point of LabTestly is to help you understand what to ask, not to replace that conversation.
Why do different labs show different ranges?
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Different labs use different equipment, reagents, and population samples to derive their ranges. That is why the reference range on YOUR report is the one to use — not a Google search for an "average" range.