Blood tests for high blood pressure: what to take and why

High blood pressure itself is diagnosed by measuring a cuff reading over time, not by a blood test — the MSD Manual and StatPearls define hypertension as a systolic reading at or above 130 mmHg or a diastolic reading at or above 80 mmHg, while the NHS and WHO describe hypertension as a reading of 140/90 mmHg or higher. No blood test replaces the measurement, and no blood test confirms or rules out hypertension on its own.

So why order blood tests at all once a raised reading turns up more than once? A new hypertension diagnosis routinely comes with a small panel of tests that answer a different question: whether high blood pressure has already affected the kidneys or heart, whether something else is driving the reading, what your overall cardiovascular risk looks like, and whether it is safe to start the medications that are usually used to treat it. This article covers that panel, what each result is checked against, and when a result should prompt urgent care. It does not cover how blood pressure itself is measured or how it is treated — for the reading itself, follow the protocol your clinician gives you, and for treatment, that decision is your clinician’s to make with you.

The panel ordered at a new diagnosis

According to the MSD Manual, the standard work-up at a new diagnosis includes “urinalysis and urinary albumin:creatinine ratio”, a “lipid panel, complete metabolic panel (including creatinine or cystatin C, potassium, and calcium), fasting plasma glucose or hemoglobin A1c, thyroid-stimulating hormone”, and an ECG. StatPearls describes a similar “blood workup including complete blood count, ESR, creatinine, eGFR, electrolytes, HbA1c, thyroid profile, blood cholesterol levels, and serum uric acid” alongside a “urine albumin to creatinine ratio” and a 12-lead ECG. Between the two sources, this covers glucose control, the full lipid panel, kidney function, electrolytes, uric acid, a blood count, a urine check for early kidney damage, and thyroid function — none of them are diagnostic of hypertension by themselves, and each answers a narrower question about what is happening alongside the raised reading.

A liver panel is not part of either source’s list for a routine new-diagnosis work-up, but your clinician may still add liver enzymes before starting certain medications, since some blood-pressure drugs are processed by the liver — whether to include it is a decision made case by case, not a fixed rule from these sources.

What an abnormal result in this panel can point to

None of these results diagnoses hypertension, but a pattern across them can point a clinician toward a specific next step:

• Raised creatinine or a low eGFR suggests the kidneys are already affected, either as a cause of the high reading or as damage from it — StatPearls lists creatinine and eGFR among the standard work-up for exactly this reason.
• Low potassium that is not explained by a diuretic is a specific clue. The MSD Manual states that “patients with hypokalemia unrelated to diuretic use are evaluated for high salt intake and for primary aldosteronism by measuring plasma aldosterone levels and plasma renin activity.” That evaluation — the aldosterone-to-renin ratio and any follow-up testing — is ordered and interpreted by a clinician; it is not a test you request or repeat on your own.
• An abnormal urine albumin:creatinine ratio flags early kidney involvement even when creatinine itself still looks normal, which is why MSD and StatPearls both include it even for a first-time diagnosis.
• An unexpected lipid panel or glucose/HbA1c result does not point to a cause of the high reading, but it changes the overall cardiovascular risk picture your clinician weighs when deciding how urgently to treat and how closely to follow up — see our heart and blood vessel tests guide for how these results fit into that wider picture.
• An abnormal TSH can mean thyroid disease is contributing to the blood pressure picture rather than being an unrelated finding.

Beyond this basic panel, a clinician who suspects a specific secondary cause may order further tests that are entirely their call to make: the MSD Manual lists plasma free metanephrines to check for a rare adrenal tumour and a sleep study when the history suggests sleep apnea, both ordered “sometimes,” alongside the aldosterone/renin testing above; a clinician may also add cortisol testing. None of these are something to ask a lab to run without a clinician directing the work-up, and an aldosterone-to-renin ratio result is not something to interpret from an online reference alone.

Preparation and factors that distort results

Fasting requirements differ by test — fasting glucose needs fasting, HbA1c does not, and a lipid panel may or may not require it depending on the laboratory and what else is being measured, so follow the instructions given with your specific request rather than a general rule. Potassium results in particular are sensitive to how the sample itself is handled, not just to what is happening in your body — see our electrolytes guide for the pre-analytical factors that can shift a potassium reading independently of your actual level. Recent illness, dehydration, and some over-the-counter and prescription medicines can also shift creatinine, potassium and glucose results, so mention everything you are taking when the panel is ordered.

Monitoring once medication starts

If you start a medicine from the ACE inhibitor, ARB or diuretic classes, potassium and creatinine are typically re-checked afterward, because these medicine classes can raise or lower potassium and can affect kidney function. The MSD Manual states that, for the basic laboratory testing described above, “testing should be repeated at least annually” — this is the only repeat interval given in the sources behind this article, and it describes the routine annual re-check for someone already on treatment, not a fixed early-monitoring schedule after a new prescription. How soon your own potassium and creatinine get rechecked after starting a new medicine is a decision your prescribing clinician makes based on which medicine, your kidney function, and your other results — follow the interval your clinician sets rather than a number from this article.

Red flags

A very high reading on its own is not usually an emergency, but a very high reading together with a severe headache, chest pain, breathlessness, vision changes, confusion, weakness on one side, or difficulty speaking is. That combination calls for emergency care right away rather than waiting for a scheduled blood draw or the next routine appointment.

Tracking these results with HealthLab

A hypertension work-up produces several numbers at once, from more than one panel, and the values that matter most over time — potassium, creatinine, the lipid panel — are the ones worth comparing across visits rather than reading in isolation. HealthLab can import a lab report from a PDF or a photo using AI recognition, or you can enter a result manually with an editable unit and reference range that matches what your own laboratory printed — manual entry is free and unlimited, and one import is free, unlimited import is Pro. Each biomarker gets its own trend chart, so a change in potassium or creatinine after a new medicine stands out against your baseline. Results can be exported to PDF to bring to an appointment, and additional profiles for family members come with Pro. HealthLab does not measure or track blood pressure itself — it organises the lab side of a hypertension work-up, alongside any other results you add.

See the labs page for the full list of what HealthLab tracks. It helps you keep this panel organised for the conversation with your clinician; it does not diagnose hypertension or decide when a result needs treatment.

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