Does Hydroxychloroquine Affect Blood Test Results?

Hydroxychloroquine (HCQ) affects a surprisingly wide range of blood test results, from cholesterol and blood sugar levels to white blood cell counts, liver enzymes, inflammatory markers, and even urine drug screens. Some of these changes reflect the drug doing its job, while others are side effects or quirks of how the drug interacts with laboratory equipment. Whether you are a patient trying to interpret your own lab work or wondering what to flag for your doctor, the picture is more varied than most people expect.

Blood Sugar and HbA1c

One of the most consistent findings in HCQ research is that the drug lowers blood sugar. A systematic review of both preclinical and clinical studies found that HCQ treatment led to meaningful reductions in fasting blood glucose, post-meal blood glucose, and hemoglobin A1c (HbA1c), the marker that reflects average blood sugar over about three months.¹ A randomized trial in people with prediabetes showed that those taking HCQ saw their glucose levels drop during an oral glucose tolerance test, while the placebo group’s glucose actually rose.² Another randomized trial confirmed modest but real decreases in both fasting glucose and HbA1c in HCQ-treated participants.³

For someone with lupus or rheumatoid arthritis who also has diabetes or is on the borderline, this matters in a practical way. Your blood sugar tests may look better than they would without HCQ, which is genuinely good news for your metabolic health. But if you stop taking HCQ for any reason, you and your doctor should expect those numbers to drift upward again. The glucose-lowering effect is tied to the drug, not to a permanent change in your body.

Cholesterol and Lipid Panels

HCQ reliably improves lipid panels, which is one reason rheumatologists view the drug favorably for patients who face elevated cardiovascular risk. In rheumatoid arthritis patients, HCQ use was associated with significantly lower total cholesterol, LDL (“bad” cholesterol), and triglycerides, along with higher HDL (“good” cholesterol), even after adjusting for factors like age, weight, and use of cholesterol-lowering medications.⁴ An earlier study found that HCQ-treated patients had cholesterol levels around 181 mg/dL compared with 205 mg/dL in untreated patients, and the benefit held regardless of whether the person was also on steroids.⁵

A randomized study in patients with rheumatoid arthritis and lupus found that total cholesterol and LDL dropped within four weeks of starting HCQ and stayed lower at eight weeks.⁶ This is relevant if you are interpreting a lipid panel and wondering whether the favorable numbers reflect your diet and exercise or your medication. In many HCQ users, both are contributing.

White Blood Cell Counts

HCQ is generally well tolerated when it comes to blood cell counts, but rare exceptions exist. One documented case involved a woman with longstanding rheumatoid arthritis who developed agranulocytosis, a dangerously low level of infection-fighting white blood cells, detected on a routine blood draw. After HCQ was stopped, her counts returned to normal within two weeks.⁷ This is a known but uncommon complication, and it is one reason periodic blood counts are part of standard monitoring for people on HCQ long term.

A related concern that has historically worried clinicians involves people with glucose-6-phosphate dehydrogenase (G6PD) deficiency, an inherited condition that makes red blood cells vulnerable to destruction by certain drugs. For decades, HCQ was assumed to carry a risk of causing hemolysis (red blood cell breakdown) in these patients, which would show up as a sudden drop in hemoglobin on blood tests. However, a thorough review of the evidence found no clinical support for this concern at standard treatment doses.⁸ The assumption appears to have been carried over from older antimalarials and never rigorously tested. This is worth knowing because some patients have been denied HCQ based on a fear that the research does not support.

Liver Enzymes

Liver function tests, specifically AST and ALT, can spike dramatically in rare cases of HCQ-related liver toxicity. One case report described a lupus patient whose AST and ALT rose to more than ten times the normal upper limit while on HCQ. The enzymes returned to normal after the drug was stopped.⁹ A broader study examining HCQ and its metabolites in patients with connective tissue diseases found that levels of one metabolite, bidesethylchloroquine, were correlated with liver function test results and red blood cell counts, suggesting the drug’s breakdown products have their own effects on these markers.¹⁰

Clinically significant liver damage from HCQ is rare enough that it turns up mostly in case reports rather than large trials. But if you are on HCQ and see a sudden jump in your liver enzymes, the drug should be on the short list of possible explanations alongside the more common culprits.

Inflammatory Markers and Autoantibodies

Because HCQ is an immunomodulatory drug, some of its effects on blood tests are the entire point of the prescription. In lupus patients treated with the usual dose of HCQ, anti-double-stranded DNA antibody levels dropped significantly within three months, and complement levels (C3 and CH50, which tend to be low when lupus is active) rose over six months.¹¹ These shifts look like improvement on paper because they reflect quieter disease activity.

In patients with primary Sjögren’s syndrome, HCQ treatment brought down erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and gamma globulin levels.¹² These are nonspecific markers of inflammation, so the drop tells you the immune system is calmer overall, not that a specific disease process has reversed.

Antinuclear antibody (ANA) titers, the test many people associate with lupus diagnosis, tend to be more stubborn. In a group of patients with undifferentiated connective tissue disease, most remained ANA-positive on HCQ, and the majority showed stable or decreased titers. Interestingly, four out of five patients who were positive for anti-dsDNA antibodies became negative on HCQ.¹³ So if you are tracking your autoantibody levels over time, HCQ can shift them, but ANA itself rarely disappears.

Antiphospholipid Antibodies

Antiphospholipid antibodies are markers tied to an increased risk of blood clots, and they are checked regularly in patients with antiphospholipid syndrome. Long-term HCQ use has been shown to reduce levels of IgG anticardiolipin antibodies and IgG/IgM anti-β2-glycoprotein I antibodies in patients with primary antiphospholipid syndrome. The reduction in anti-β2-glycoprotein I IgG was statistically significant when compared to patients not taking HCQ.¹⁴

However, in a smaller study of patients with antiphospholipid antibodies, HCQ did not significantly change a range of clotting and inflammatory markers when measured before and after starting treatment. Thromboelastography results (a way to assess overall clotting function), complement breakdown products, and CRP were essentially unchanged.¹⁵ The takeaway is that HCQ may gradually lower antiphospholipid antibody levels over months to years, but it does not produce a dramatic short-term shift in clotting tests.

Cardiac and Muscle Markers

Long-term, high-cumulative-dose HCQ use can cause toxicity in both heart and skeletal muscle, and this shows up on blood tests as elevated creatine kinase (CK), troponin, and NT-proBNP. One well-documented case involved a woman who had taken HCQ for years and presented with a CK of 830 U/L (normally well under 200), along with troponin I levels ranging from 1,800 to 3,500 ng/L (normal is under 54) and NT-proBNP between 145 and 330 ng/L (normal under 100). After stopping HCQ, her CK normalized within four months, though the cardiac markers remained elevated.¹⁶ In a broader review of chloroquine and hydroxychloroquine myopathy cases, nine patients had elevated CK levels, with values as high as roughly 1,200 U/L.¹⁷

Muscle and cardiac toxicity from HCQ tends to occur with prolonged use over many years, often at higher doses or in people with kidney impairment that slows drug clearance. If you have been on HCQ for a long time and a blood test reveals unexpectedly high CK or troponin, HCQ toxicity should be considered. It is an underrecognized cause because clinicians do not always connect these lab findings to a drug the patient has been tolerating well for years.

Potassium Levels

A recently reported case adds a new laboratory finding to the HCQ landscape: low potassium caused by the drug driving excess potassium loss through the kidneys. A 38-year-old woman on therapeutic-dose HCQ developed repeated episodes of symptomatic low potassium. Urine testing confirmed that her kidneys were inappropriately dumping potassium. When HCQ was stopped for two weeks, potassium normalized. Restarting HCQ at a lower dose reproduced the problem, and discontinuing it again resolved it.¹⁸ This is a single case report, so it is unclear how common the phenomenon is, but it suggests HCQ should be on the list of possible explanations for unexplained low potassium in a patient taking the drug.

Ferritin and Iron Handling

HCQ can influence iron-related lab values, though the effects depend on context. In patients with porphyria cutanea tarda, a condition where excess iron contributes to disease, low-dose HCQ did not lower serum ferritin the way phlebotomy (blood removal) did, even though both treatments were comparably effective at controlling the disease.¹⁹ The underlying mechanism likely involves how chloroquine-class drugs raise pH inside cellular compartments, which blocks the release of iron from transferrin, the protein that carries iron in the blood.²⁰ In practice, if you are on HCQ and your ferritin is checked, the drug is unlikely to move the number in a direction that confuses clinical decisions, but it is worth knowing the interaction exists.

False Positives and Lab Assay Interference

This is a category most patients never think about: HCQ can physically interfere with some laboratory instruments and assays, producing results that are flat-out wrong. In a case of HCQ overdose, urine drug screens produced false signals for buprenorphine, cotinine (a nicotine metabolite), oxycodone, and THC (the active compound in marijuana). The same high urine concentrations of HCQ also interfered with quantitative tests for microalbumin (used to check kidney function) and urine myoglobin.²¹ These interferences were documented at the extremely high drug levels that follow an overdose, not at normal therapeutic levels, but the mechanism means some interference is theoretically possible whenever drug concentrations in urine are unusually high.

On the other hand, a study specifically testing whether HCQ could cause a false-positive amphetamine screen found that it did not, even at concentrations far beyond what any patient would have.²² So the risk of false positives depends on the specific assay being used. If you are on HCQ and face a urine drug screen, particularly in a setting where a false positive could have consequences, it is reasonable to mention the medication beforehand.

When Your Doctor Measures HCQ Itself

HCQ blood levels are increasingly being ordered to check whether patients are actually taking the drug as prescribed and whether they are in a therapeutic range. The drug concentrates inside red blood cells, so whole-blood measurements give about twice the concentration found in serum or plasma. One study found average whole-blood HCQ levels of about 916 ng/mL compared with 469 ng/mL in serum, with a strong correlation between the two.²³ Another study confirmed this roughly two-fold difference and found that whole blood gave the most reproducible results, with a measurement variability of about 3%, compared with 14% for serum and 39% for plasma.²⁴

What this means for you as a patient is that the same level of HCQ in your body can produce very different numbers depending on whether the lab tested your whole blood, serum, or plasma. If your level looks low and your doctor is wondering about adherence, the sample type matters. Whole blood is considered the preferred matrix, and results from serum or plasma should be interpreted with that variability in mind.

HCQ in Pregnancy and Neonatal Blood Work

HCQ is one of the few autoimmune medications widely considered safe to continue during pregnancy, and it crosses the placenta. A large study examining in-utero HCQ exposure found that babies exposed to the drug had a reduced odds of developing cutaneous neonatal lupus compared to unexposed babies, with about 16% of neonatal lupus cases having been exposed to HCQ versus 34% of controls.²⁵ This does not directly alter neonatal blood test results, but it tells clinicians that the drug’s immunomodulatory effects operate in the fetus as well. A newborn whose mother took HCQ will carry detectable drug levels, which may subtly influence inflammatory markers in early blood work.

The broader point is that HCQ’s reach extends beyond the person swallowing the pill. If you are pregnant and on HCQ, your baby’s early lab results exist in a slightly different context than those of a baby whose mother was not on the drug. Pediatricians managing neonatal lupus or interpreting newborn labs should be aware of the exposure history.

What to Tell Your Doctor

Keeping HCQ on your active medication list is the single most useful thing you can do to help anyone interpreting your blood work. The drug’s effects span lipid panels, glucose markers, liver enzymes, white blood cell counts, inflammatory markers, autoantibodies, and potentially electrolytes and cardiac markers. Some of these shifts are desirable, some are harmless, and a few are warning signs of toxicity. Without knowing you are on HCQ, a clinician looking at improved cholesterol might credit your diet, or one seeing elevated liver enzymes might order an unnecessary workup. The drug’s fingerprints are all over routine lab panels, and the only reliable way to read them correctly is to know the drug is there.