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Learn how HLA-DR and CD38 flow cytometry measures activated T cells, what high results may mean, why ranges vary, and how clinicians plan follow-up.

Activated T-Cell Marker Test: HLA-DR, CD38, Immune Activation, and Inflammation

Understand how CD19 and CD20 B-cell counts are measured, why results may be high or low, how anti-CD20 therapy affects them, and which follow-up tests assess antibody function.

B-Cell Count Test: CD19, CD20, Immune Function, and Antibody Production

Learn what a CD4 count measures, how HIV affects helper T cells, what common ranges and thresholds mean, why results fluctuate, and how the test guides monitoring and infection prevention.

CD4 Count Test: Helper T Cells, Immune Function, HIV Monitoring, and Meaning

Learn how the CD4/CD8 ratio is calculated, what low or high results may mean, why an inverted ratio is nonspecific, and how the test adds context in HIV and immune monitoring.

CD4/CD8 Ratio Test: Immune Balance, High and Low Ratio, and Meaning

Learn what a CD8 count measures, why cytotoxic T-cell numbers may rise or fall, how viral infections affect results, and why cell quantity does not equal antiviral function.

CD8 Count Test: Cytotoxic T Cells, Immune Function, and Viral Response

Understand what a chemokine panel measures, why immune-signaling and cell-migration markers rise or fall, and how specialists interpret patterns and limitations.

Chemokine Panel Test: Immune Signaling, Inflammation, and Cell Migration Markers

Diagnostics

Home Diagnostics Page 16

Understand progesterone testing for ovulation, luteal timing, fertility, and pregnancy, including result cutoffs, units, medication effects, limitations, and follow-up.

Progesterone Test in Women: Ovulation, Luteal Phase, Pregnancy, and Results

Understand prolactin testing in women, including high and low results, period and fertility effects, repeat-test preparation, medication causes, macroprolactin, MRI, and treatment.

Prolactin Test in Women: High Levels, Period Changes, Fertility, and Results

Understand SHBG testing in women, including high and low causes, PCOS patterns, total versus free testosterone, birth control effects, preparation, calculations, and follow-up.

Sex Hormone-Binding Globulin (SHBG) Test in Women: High, Low, PCOS, and...

Understand testosterone testing in women, including high levels, PCOS and hair-growth patterns, total versus free results, SHBG, accurate testing, causes, and treatment.

Testosterone Test in Women: High Levels, PCOS, Hair Growth, and Results

Understand why an 11-deoxycortisol test is ordered, how baseline and metyrapone results differ, and what high or low levels may mean for adrenal enzyme function.

11-Deoxycortisol Test: Adrenal Enzyme Deficiency and Results

Learn how the 17-hydroxyprogesterone test screens for congenital adrenal hyperplasia, why levels rise, when ACTH stimulation is used, and how results are confirmed.

17-Hydroxyprogesterone (17-OHP) Test: Adrenal Hyperplasia, High Levels, and Results

Learn how to collect a 24-hour urine free cortisol sample, what high or normal results mean, and how the test fits into accurate Cushing syndrome screening.

24-Hour Urine Free Cortisol Test: Cushing Syndrome Screening and Results

Learn how a 24-hour urine metanephrines test screens for pheochromocytoma and paraganglioma, how to collect it correctly, and what high or borderline results mean.

24-Hour Urine Metanephrines Test: Pheochromocytoma Screening and Results

Understand the ACTH blood test, including why ACTH and cortisol are paired, what high or low patterns suggest, and how pituitary and adrenal causes are confirmed.

ACTH Blood Test: High, Low, Normal Range, Pituitary, and Adrenal Results

Learn how the ACTH stimulation test measures cortisol reserve, why modern assay cutoffs differ, what abnormal results mean, and when a normal response may be misleading.

ACTH Stimulation Test: Adrenal Insufficiency, Cortisol Response, and Results

Learn why no validated adrenal fatigue test exists, which cortisol tests diagnose real adrenal insufficiency, and how to investigate fatigue safely without risky hormone products.

Adrenal Fatigue Test: Cortisol Testing, Symptoms, Limitations, and What Results Mean

Understand an adrenal hormone panel covering cortisol, ACTH, aldosterone, renin, and DHEA-S, including preparation, result patterns, and confirmatory testing.

Adrenal Hormone Test Panel: Cortisol, ACTH, Aldosterone, Renin, DHEA-S, and Results

Learn how cortisol, ACTH, renin, aldosterone, electrolytes, and cosyntropin results distinguish primary from central adrenal insufficiency and guide urgent care.

Adrenal Insufficiency Test Panel: Cortisol, ACTH, Renin, Aldosterone, and Results

Learn what an aldosterone blood test shows, why renin must be measured with it, how high and low patterns affect blood pressure, and which follow-up tests confirm the cause.

Aldosterone Blood Test: High, Low, Normal Range, Blood Pressure, and Results

Learn how the aldosterone–renin ratio screens for primary aldosteronism, how medicines and potassium affect it, and what positive, negative, or borderline results mean.

Aldosterone-Renin Ratio (ARR) Test: Primary Aldosteronism, Blood Pressure, and Results

Learn why androstenedione is tested, what high or low levels may mean, how adrenal and gonadal sources differ, and which follow-up hormones confirm the cause.

Androstenedione Blood Test: High, Low, Adrenal Hormones, and Results

Learn how a CAH test panel uses 17-OHP, cortisol, androgens, renin, aldosterone, stimulation, and genetics to identify enzyme deficiencies and monitor treatment safely.

Congenital Adrenal Hyperplasia (CAH) Test Panel: 17-OHP, Androgens, and Results

Learn how timing, stress, medicines, binding proteins, ACTH, and dynamic testing determine what high, low, or normal cortisol blood results mean for adrenal function.

Cortisol Blood Test: High, Low, Normal Range, Stress, and Adrenal Function

Learn how late-night cortisol, 24-hour urine free cortisol, dexamethasone suppression, ACTH, imaging, and repeat testing work together to diagnose Cushing syndrome.

Cushing Syndrome Test Panel: Late-Night Cortisol, Urine Free Cortisol, Dexamethasone, ACTH,...

Understand what a deoxycorticosterone (DOC) blood test measures, why high DOC can cause low-renin hypertension and low potassium, and how results are interpreted.

Deoxycorticosterone (DOC) Test: Adrenal Hormone, Blood Pressure, and Results

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