Top 10(-ish) Lab Tests You Should Consider

Written By Subhashini .

(even if you’re feeling “fine”)

Why do lab testing if you’re feeling “fine”? Well to start, I’d argue that our definition of “fine” is probably a little skewed. We frequently brush off common symptoms like fatigue, brain fog and difficulty focusing, thinking that they’re probably just due to stress or lack of sleep. While sleep and stress can absolutely impact our energy levels and mental focus, there could actually be many other root causes for these symptoms.

Also, by the time we feel significant symptoms, our bodies have often been out of balance for a long time. A perfect example is type 2 diabetes. By the time someone is diagnosed with type 2 diabetes, their body has usually been insulin resistant for at least 7-10 YEARS. Shocking, right?! But since people typically do not experience troublesome symptoms of insulin resistance until later stages of the disease process, they often miss out on that 7-10 year period…UNLESS they get regular blood testing done. The sooner we can detect insulin resistance, the sooner we can implement lifestyle changes +/- medication that can help not only prevent the progression of insulin resistance, but also actually reverse the disease process, in many cases. I have heard many times from patients that they were caught off guard by their pre-diabetes or diabetes diagnosis. But it doesn’t have to be that way!

If we don’t know what’s going on under the surface, it limits our ability to take steps to ensure we maintain our best possible health. The good news is that the simple blood tests I’ve listed below can be ordered by any healthcare provider, including your primary care provider, to help you better understand the current state of your health and also gain insights into possible future concerns.

Reference Range vs. Optimal Range

A quick word about interpretation of lab results. The reference range listed for any particular lab test is NOT the same as the optimal range. The reference range represents the statistically derived average of lab values observed in a population of apparently healthy individuals. It typically encompasses the middle 95% of results from that group. Being within the reference, or “normal,” range simply indicates that your results are not at the extreme ends of the population values. It does not necessarily mean your body is functioning optimally. The optimal range is the range where the body’s systems are working most efficiently and resiliently and is typically based on a combination of research studies, clinical outcomes and practitioner experience. I will list some optimal ranges for the labs below when appropriate.

Now let’s take a closer look at the top 10-ish lab tests that I think everyone should consider, and why they are important. (And yes, I know I’m cheating a little because some of my recommendations are panels that include more than one test. But I couldn’t pare down the list anymore!) These are blood tests that I routinely order on my patients, and have had tested myself.

The List:

1.     CBC (complete blood count) with differential and CMP (comprehensive metabolic panel)

2.     Full thyroid panel (TSH, FT4, FT3, TPO Abs and Tg Abs)

3.     Vitamin D

4.     Hemoglobin A1C

5.     Fasting insulin

6.     Advanced lipid panel (total cholesterol, HDL, TG, LDL, LDL-particle number, ApoB, Lp(a))

7.     Iron Panel

8.     Micronutrients: B12, RBC Magnesium, RBC Zinc

9.     Homocysteine

10.  hs-CRP

The Details:

1.  Complete Blood Count (CBC) with Differential and Comprehensive Metabolic Panel (CMP)

CBC with Differential

  • A CBC measures your white blood cells (WBCs), red blood cells (RBCs), and platelets

  • WBCs are a part of your immune system—too high can indicate infection, inflammation, or stress; too low can mean immune suppression, nutrient deficiencies, or certain viral infections.

  • The differential shows a breakdown of the amounts of the five main types of WBCs. Elevations or decreases in different types of WBCs can provide hints as to what might be going on in the body, i.e. bacterial vs. viral infection, allergies, etc.  

  • RBCs/Hemoglobin/Hematocrit: Detects anemia, dehydration, or blood loss.

  • RBC Indices (MCV, MCH, MCHC, RDW): These values can help determine the type and cause of anemia. For example, MCV (mean corpuscular volume) tells us the average size of your red blood cells. An elevated MCV can indicate B12 or folate deficiency, and a low MCV can indicate iron deficiency or a chronic disease, such as kidney disease or an autoimmune disease.

  • Platelets: These cells help with blood clotting and healing. Too many or too few can signal clotting issues, inflammation, or bone marrow problems.

CMP

  • A CMP includes 14 markers and provides insights on how well your liver, kidneys, and metabolism are working.

  • Sodium/potassium/chloride/carbon dioxide: These electrolyte levels impact our hydration, fluid balance, nerve and muscle function and also tell us about our kidney function because our kidneys are responsible for filtering our blood and excreting excess electrolytes through our urine.

  • BUN, Creatinine, BUN/Creatinine Ratio, eGFR: These markers tell us about your kidney function and show how well your body filters and eliminates waste.

  • Glucose: Tells us about blood sugar regulation. It is an especially valuable marker when tested while fasting (nothing to eat or drink except water for 8-10 hours prior to lab draw). Optimal fasting glucose is < 85 mg/dL, even though the upper limit of the lab reference range is 99 mg/dL. If you have multiple years’ worth of fasting glucose levels, it can be valuable to look at the trend of your fasting glucose to see if you are trending towards insulin resistance (gradually increasing fasting glucose levels). Keep in mind that fasting glucose is just one marker of blood sugar regulation in the body. A fasting glucose level tells us mostly about blood sugar regulation over the last 24 hours or so, so it only tells part of the story. This is why it’s so important to consider other markers, including fasting insulin and hemoglobin A1C level, to get a more complete picture of glucose regulation in the body.

  • AST, ALT, ALP, Total bilirubin, Total protein, Albumin, Globulin, Albumin/Globulin Ratio: These markers assess how efficiently your liver processes toxins, produces proteins, and manages metabolism. Elevations in AST and/or ALT can indicate liver inflammation, damage or fatty liver.

2.   Full Thyroid Panel (TSH, FT4, FT3, TPO Abs and Tg Abs)

  • TSH (thyroid stimulating hormone): This is a brain hormone that tells your thyroid gland whether to produce more or less thyroid hormone. An elevated TSH indicates hypothyroidism (underactive thyroid gland) and a low TSH indicates hyperthyroidism (overactive thyroid gland). The reference range for TSH at most labs is 0.40 - 4.5 mIU/L. The upper limit of the optimal range, however, is somewhat disputed (PMID 31662841). Most Functional Medicine providers consider 2-2.5 mIU/L to be the optimal range because we often see a significant improvement in how patients with hypothyroidism on thyroid hormone replacement medication feel when their TSH is maintained within this range. However, treating hypothyroidism is a very nuanced subject and entails more than simply medication (a subject for another post!).

  • FT4 (Free T4), FT3 (Free T3): These are your actual thyroid hormones (vs. TSH, a brain hormone). Free T4 is the inactive thyroid hormone that your thyroid gland produces. It must be activated (converted) to free T3, the active hormone responsible for important functions throughout the body, including energy production, digestion, brain function, and metabolic rate. It is possible for the TSH level to be within the reference range (0.40 - 4.5 mIU/L) but the free T4 and/or free T3 to be suboptimal, and this can contribute to symptoms. This is why it is so important to test more than just the TSH level. Through dietary modification, optimization of key nutrients and lifestyle changes we can optimize free T4 and free T3 levels, and my patients often notice an improvement in how they feel (i.e. improved energy, less joint pain, resolved constipation).

  • TPO Abs (Thyroid peroxidase antibodies) and Tg Abs (Thyroglobulin antibodies): These tests tell us whether your immune system is producing antibodies against and attacking your thyroid gland. Elevated levels of one or either of these antibodies may indicate an autoimmune disease called Hashimoto’s thyroiditis. While treatment of autoimmune hypothyroidism and non-autoimmune hypothyroidism both usually require medication, there are additional dietary and lifestyle changes that can benefit those with autoimmune hypothyroidism. Thus knowing the type of hypothyroidism an individual has is important. TPO and Tg Abs can often detect autoimmune thyroiditis years before the TSH level becomes abnormal. Early detection allows us to intervene before thyroid tissue is permanently damaged.

3.  Vitamin D (25-Hydroxy)

  • Fun fact: Vitamin D is actually a hormone, not a vitamin!

  • You most likely think of bone health when you hear vitamin D. But vitamin D influences many functions in the body, including immune function, inflammation, calcium metabolism, cardiovascular health, thyroid function, mood/mental health, gut health and cancer risk.

  • Most of the current guidelines for vitamin D levels are bone-centric, meaning, they focus on the level of vitamin D needed to reduce the risk of bone diseases like osteoporosis and reduce the risk of fractures. They do not take into consideration the many other functions of vitamin D in the body.

  • Reference range at most labs is 30-100 ng/mL. Optimal range is 40–70 ng/mL.
    References: PMID: 39861407

4.   Hemoglobin A1C 

  • Hemoglobin A1C reflects your average blood sugar over the past three months, and is reported as a percentage. The higher the percentage, the higher your blood sugar has been on average.

  • Glucose (sugar) in your blood naturally attaches to hemoglobin, the protein in red blood cells that carries oxygen. Since the lifespan of red blood cells is about 90–120 days, the A1C reflects your average blood sugar during that time.

  • An elevation in A1C level is actually a rather late sign of insulin resistance. We will not see the A1C level rise until months or years after the pancreas has been secreting more and more insulin to maintain your blood sugar level within a healthy range. This is why testing a fasting insulin level regularly is valuable (coming up next!).

  • Lab Reference Ranges:

    • Normal: <5.7%

    • Pre-diabetes: 5.7-6.4%

    • Diabetes: 6.5 or higher

  • Keep in mind that insulin resistance is a spectrum. There is nothing magical that happens at the cut-off level of 5.7 that suddenly makes someone who has an A1C of 5.8 insulin resistant and someone with an A1C of 5.6 not insulin resistant. Both individuals have insulin resistance! It’s just that based on research, we have set a cut-off level, above which research has shown the risk of developing diabetes and other chronic diseases, including heart disease, increases. So while that cut-off is important, simply being lower than a cut-off doesn’t mean that there’s no concern. I’ve had too many patients tell me they were shocked when they were diagnosed with pre-diabetes because their provider had never told them to change their diet or lifestyle based on their lab results at their previous annual visits. But their lab trends show their A1C has been gradually creeping higher and higher over the last 5-10 years.

  • It is possible to lower your A1C level and reverse insulin resistance through lifestyle changes! My A1C level was in the pre-diabetes range about 11 years ago, despite not being overweight. With diet and lifestyle changes, I have been able to lower and maintain my A1C in the low 5-range. It’s never too late to make lifestyle changes that can have lasting effects on your health!

5.    Fasting Insulin

  • When glucose enters the bloodstream after a meal, it stimulates the pancreas to release insulin, a hormone that helps your cells to take in glucose from your bloodstream so they can use it for energy.

  • A fasting insulin level shows us how hard your pancreas is working (by pumping out insulin) to control your blood sugar.

  • An elevated fasting insulin level is often one of the earliest indicators of the start of insulin resistance. It is indicating that your pancreas is needing to secrete so much insulin to maintain your blood glucose level within range, that even 8-10 hours of fasting was not enough to allow your insulin level to come back down to the optimal range.

  • Reference range at most labs is ≤18.4 uIU/mL. Optimal range is ≤5 uIU/mL.

  • It is possible to lower your fasting insulin level through lifestyle changes!

6.   Advanced Lipid Panel: total cholesterol, HDL, TG, LDL, LDL-particle number, ApoB, Lp(a)

  • Total cholesterol: Represents the overall amount of cholesterol in your blood and is calculated as the sum of your HDL-cholesterol, LDL-cholesterol and a portion of your triglycerides.

  • HDL-cholesterol (high density lipoprotein): Often referred to as “good cholesterol.” HDL helps carry cholesterol out of your arteries and back to your liver, where it can be broken down and removed from the body. Higher HDL levels are linked to lower risk of heart disease. Optimal level is >50 mg/dL.

  • TG (triglycerides): A type of fat in your blood that your body uses for energy. When you eat excess calories, especially sugar and refined carbs (i.e. white bread, white rice, pasta, cookies, cakes, sugars), than you burn, your body stores the excess as triglycerides. While lab reference ranges recommend keeping TG <150, from a Functional Medicine approach we recommend TG <100 mg/dL for optimal metabolic and cardiovascular health. This can often be achieved through diet and lifestyle change alone.

  • LDL-cholesterol (low density lipoprotein): LDL’s job is to deliver cholesterol from your liver to your tissues, to be used for critical functions like hormone production (i.e. estrogen, testosterone, cortisol, vitamin D) and cell repair. It is often referred to as “bad cholesterol” because high levels — especially when the LDL particles are small, dense, or oxidized — can lead to plaque (deposits of cholesterol, inflammatory cells, calcium and other substances) buildup in the inner walls of arteries, which can contribute to heart disease and strokes. I don’t like to use the term “bad cholesterol” because that’s not the whole story. We need some LDL cholesterol to stay healthy. Optimal level is <100 mg/dL, along with low ApoB and LDL-P.

  • LDL-particle number (LDL-P): LDL-P measures how many LDL particles are circulating in your bloodstream — not just how much cholesterol they’re carrying (LDL-cholesterol test). Think of LDL particles as cars. LDL-P measures how many cars you have on the road (your arteries). LDL particles come in different sizes. When LDL particles become small and oxidized, when inflammation is present, they can enter artery walls and contribute to plaque buildup. So cardiovascular risk is not just associated with how much LDL-cholesterol you have — it also matters what kind (size and number). People with insulin resistance or metabolic syndrome often have normal LDL-cholesterol but high LDL-P, which puts them at hidden risk. The exciting part is that LDL-cholesterol and LDL-P can both be improved with diet and lifestyle changes! Optimal LDL-P is <1000 nmol/L.
    References:     PMID 36522243, PMID 19657464

  • Lp(a) (lipoprotein a): Lp(a) is similar to LDL-cholesterol but with an extra protein called apolipoprotein(a) attached. This extra protein makes Lp(a) “stickier”, which means it can more easily enter and attach to artery walls and promote plaque buildup. Lp(a) is a genetic risk factor for cardiovascular disease. It is possible to have all your cholesterol levels within the reference or even optimal ranges, and have a high Lp(a) level. There is no evidence that diet or lifestyle change can impact Lp(a) level. But knowing your level is important because it helps to better determine your risk for cardiovascular disease and can guide treatment approach.
    References:     PMID: 35583875

  • ApoB (apolipoprotein B): ApoB is a protein found on every LDL, IDL (intermediate density lipoprotein), VLDL (very low density lipoprotein), and Lp(a) particle — all particles that can contribute to plaque-formation (atherogenic). Since each of these particles has only one ApoB protein, measuring ApoB level directly counts the number of these circulating atherogenic particles. For this reason, it has been found to be a more accurate predictor of cardiovascular risk than LDL-cholesterol or even LDL-P alone. Optimal level is <80 mg/dL.
    References: PMID: 37517561, PMID: 40887080, PMID: 38950110

7.   Iron Panel (total iron, iron binding capacity, % saturation, ferritin)

  • Iron plays a critical role in oxygen transport, energy production and immune function.

  • An iron panel helps us understand how well your body is absorbing, transporting, and storing iron. Total iron is the amount of iron circulating in the blood right now. Ferritin measures the amount of iron stored in the body. It can sometimes be elevated in response to inflammation, for example, during an infection.

  • Both iron deficiency and iron overload (too much iron) cause problems. Iron deficiency can be a significant contributor to fatigue, brain fog, thyroid dysfunction, poor concentration, elevated resting heart rate and shortness of breath with minimal exertion. Iron overload can cause oxidative damage to organs. Iron deficiency is much more common than iron overload.

  • It is possible, and quite common actually, to have iron deficiency without anemia. When a patient comes in complaining of fatigue, many providers often test a CBC to rule out anemia, but fail to order an iron panel. Correcting iron deficiency, even if there is no anemia, can significantly improve symptoms, including fatigue.

8.   Micronutrients: B12, RBC Magnesium, RBC Zinc

B12

  • B12 is critical for red blood cell formation, energy production, methylation (key process in detoxification and repair processes), neurological function and DNA synthesis.

  • Serum (blood) B12 can appear normal while cellular B12 (the B12 within our cells) is inadequate, but we don’t have a great way to measure cellular B12 at this time. Testing a homocysteine level along with B12 is helpful, because in early stages of B12 deficiency or insufficiency, serum B12 may be normal but homocysteine level may be elevated, signaling to us that there’s an increased need for B12.   

  • Our body cannot make B12, so we must get it from our diet or through supplementation.

  • The reference range for B12 at most labs is 200-1100 pg/mL. Optimal range is at least 500 pg/mL, staying within the reference range.

RBC (red blood cell) Magnesium

  • Magnesium is essential for over 300 biochemical reactions in the body. It is a common nutrient deficiency among Americans.

  • Magnesium is important for energy production, muscle and nerve function, blood sugar control, heart rhythm, and stress regulation. Low or insufficient magnesium levels can contribute to muscle tension, anxiety, sleep disturbances, headaches/migraines and constipation.

  • RBC magnesium is a more accurate measure of magnesium in the body than is serum magnesium level, however, it still does not fully capture cellular magnesium status. Thus if patients notice an improvement in symptoms with magnesium supplementation, I recommend continuing with supplementation, under the guidance of a healthcare provider.

RBC Zinc

  • Zinc plays an important role in immune function, wound healing, neurotransmitter balance, hormone balance, thyroid function,

  • Similar to magnesium testing, RBC zinc is a more accurate measure of zinc in the body than is serum zinc level.

9.   Homocysteine

  • Homocysteine is an amino acid (building block of proteins).

  • Several B vitamins, including B12, are required to convert homocysteine to other compounds. Insufficient levels of B12 can contribute to an elevated homocysteine level.

  • An elevated homocysteine level has been associated with higher cardiovascular risk (i.e. heart disease, stroke). The homocysteine level can be lowered into an optimal range using B vitamin supplementation.

  • The reference range for homocysteine at most labs is ≤15 µmol/L. Optimal range is 6–9 µmol/L.

10.   hs-CRP (high sensitivity C-reactive protein)

  • CRP (C-reactive protein) is a protein produced by the liver in response to inflammation, infection, or tissue damage in the body.

  • A standard CRP or a hs-CRP blood test can be done. Both tests measure the level of CRP. The difference lies in how sensitive the test is and what level of inflammation it can detect. A standard CRP test detects high levels of inflammation and is used to monitor inflammation from conditions like bacterial infections, some autoimmune diseases, or major injuries. Hs-CRP, as the name suggests, is highly sensitive and can detect low-grade, chronic inflammation. It is most often used to assess long-term risk for cardiovascular disease in otherwise healthy individuals. Levels over 3 mg/L are considered higher risk, while levels under 1 mg/L are considered low risk. 

If you’d like to learn more about working with me to know your numbers, schedule a free discovery call HERE.

Subhashini .