🩸 Hemoglobin High and You Are Not on Testosterone

What this panel can settle, and by what logic

Eight markers that sort a raised hemoglobin into the three buckets it can belong to: too little plasma, too many red cells made for a reason, or a marrow making them on its own.

1. Iron status is the fork in the road and it costs about nineteen dollars. A marrow being driven to make red cells consumes iron, so a genuinely expanded red cell mass usually arrives with a falling Ferritin, a falling saturation on the Iron Panel (Iron, TIBC, Transferrin Saturation) and smaller cells. A hematocrit that is high because plasma volume is low leaves all three untouched. In the JAK2-unmutated erythrocytosis literature, iron studies are part of the first-line assessment for exactly this reason Gangat 2025.
2. Total Testosterone belongs here even in somebody taking nothing. Androgens are the most reliably erythropoietic exposure in this population: in a large cohort of trans men on testosterone, erythrocytosis was common enough to be studied as an expected consequence rather than an adverse surprise Madsen 2021. Drug-induced erythrocytosis has now been reviewed systematically as its own entity Liu 2025, and testosterone is the largest single contributor to it.
3. Cystatin C with eGFR and Urinalysis, Routine cover the uncommon cause that matters. A renal lesion secreting erythropoietin is rare and it announces itself through blood in the urine or an unexplained fall in filtration. Cystatin C is used rather than creatinine because creatinine-based and cystatin-based filtration estimates disagree systematically, and the disagreement is largest in the muscular Wang 2023.
4. The Complete Blood Count (CBC) with Differential itself carries the platelet and white cell counts, and a raised hemoglobin sitting beside a raised platelet count is a different conversation from a raised hemoglobin alone.
5. hs-CRP (High-Sensitivity C-Reactive Protein) is here because a normal Ferritin means nothing without it Luo 2023, and this panel turns on the ferritin being readable.

The base rate matters. In a Canadian chart review of patients sent for molecular testing because polycythemia vera was suspected, secondary causes were identified in most of them, and sleep apnea, testosterone and smoking dominated the list Chin-Yee 2022. That is the shape of this panel: it is built to find the common explanation first.

What it cannot settle, and what would

It cannot diagnose sleep apnea, which is the likeliest answer. Obstructive sleep apnea causes intermittent overnight hypoxia and chronic erythropoietin drive, and it is both very common and very commonly undiagnosed Platon 2023. No blood marker detects it. A home sleep study is the test, and snoring plus daytime sleepiness plus a raised hematocrit is enough to justify one before anything else on this list.

It cannot exclude a primary bone marrow cause. Serum erythropoietin and the JAK2 V617F mutation are the two tests that sort primary from secondary erythrocytosis, and neither is in this catalog Gangat 2025. A persistently high hematocrit with normal iron studies, no androgen exposure and no sleep or smoking explanation is a hematology referral.

It cannot measure red cell mass directly. Hematocrit is a ratio, so it rises when the numerator grows and when the denominator shrinks, and the only way to separate the two definitively is an isotope-dilution red cell mass study that almost nobody does any more.

And it cannot tell you your cardiovascular risk from the number. The threshold at which a raised hematocrit becomes a thrombotic risk in secondary erythrocytosis is genuinely unsettled, and routine venesection in secondary cases is not the automatic answer it is in the primary ones Gangat 2025. Removing blood without finding the cause treats a number.

Draw conditions that decide whether the money is wasted

Hydration status is the entire game here, because hematocrit is a ratio and dehydration moves the denominator.

1. Do not draw dehydrated. An early-morning fasted draw after a sauna, a long flight or a hard session can lift hematocrit by several points and manufacture the finding you came to explain. Drink normally the evening before and the morning of.
2. Sit for five minutes before the needle and keep the tourniquet brief. Standing shifts plasma out of the vessels and a prolonged tourniquet concentrates the sample locally; both raise a measured hematocrit without changing a single red cell.
3. No alcohol for 48 hours and no return from altitude within a week. Both change the value for reasons that have nothing to do with what you are testing for Chin-Yee 2022.
4. Fast 9 to 12 hours for the Comprehensive Metabolic Panel (CMP), and note on the requisition whether you smoke or vape, because carbon monoxide exposure drives erythropoiesis and it is the one cause you can stop this week.

How you would know it answered your question, and what each pattern means next

Four patterns, and the marker that would move if each explanation is the right one.

• High hematocrit with low Ferritin, low saturation and small cells: production is being driven and iron is being consumed. Find the driver. If it is sleep apnea, treatment lowers the hematocrit within months and that fall is the confirmation Platon 2023.
• High hematocrit with completely normal iron studies: plasma volume is the likelier explanation. Repeat under the draw conditions above; a substantial share of these normalize Chin-Yee 2022.
• High or high-normal Total Testosterone in somebody taking nothing: confirm on a second morning draw before concluding anything, then treat it as the probable driver Liu 2025.
• Blood or protein on the Urinalysis, Routine, or a reduced Cystatin C with eGFR filtration rate: the kidney becomes the priority and this stops being a blood-count question Gangat 2025.

Sources read for these sections

• Chin-Yee B, et al. Secondary causes of elevated hemoglobin in patients undergoing molecular testing for suspected polycythemia vera in southwestern Ontario: a chart review. CMAJ Open 2022 · PMID 36347562
• Gangat N, et al. JAK2 Unmutated Erythrocytosis: 2026 Update on Diagnosis and Management. American Journal of Hematology 2025 · PMID 41123216
• Platon AL, et al. An Update on Obstructive Sleep Apnea Syndrome-A Literature Review. Medicina (Kaunas) 2023 · PMID 37629749
• Liu J, et al. Diagnosis, management, and outcomes of drug-induced erythrocytosis: A systematic review. Blood Advances 2025 · PMID 39913688
• Madsen MC, et al. Erythrocytosis in a Large Cohort of Trans Men Using Testosterone: A Long-Term Follow-Up Study on Prevalence, Determinants, and Exposure Years. Journal of Clinical Endocrinology and Metabolism 2021 · PMID 33599731
• Luo H, et al. A Practical Guide to Adjust Micronutrient Biomarkers for Inflammation Using the BRINDA Method. Journal of Nutrition 2023 · PMID 36792034
• Wang Y, et al. Discordance Between Creatinine-Based and Cystatin C-Based Estimated GFR: Interpretation According to Performance Compared to Measured GFR. Kidney Medicine 2023 · PMID 37753251