Blood chemistry panels of 6, 12, 24 and 35 markers: what each includes and which to order

The order says “blood chemistry of 24 elements”, or the lab offers you the 35 “so everything shows”. It is the most common way to order a blood test in Mexico and, at the same time, one of the least explained: the number is not a medical standard but a commercial name, and what each version carries changes from one lab to another. This text explains which blocks make it up, what each answers, which version suits, what needs fasting and how to read a value “slightly off”.

Before going on, a distinction. Choosing between 6 or 35 markers is a calm decision, to be made without hurry and with your doctor. What does not wait for that decision are symptoms: yellow skin or eyes, severe abdominal pain, confusion or unusual drowsiness, vomiting or diarrhoea that will not stop. With any of those, you do not choose a panel: you seek care now.

The number is not a standard, it is a commercial name

There is no official definition of “blood chemistry of 12 elements”. Each lab builds its packages with the markers it decides, and two labs can sell a “24” with different lists. That is why the useful question is not how many markers it carries, but which blocks: glucose, kidney, lipids, liver, electrolytes and, in the long versions, a few extras.

Where there are definitions is in the international panels, and they serve as a map. The basic metabolic panel measures eight substances: glucose, calcium, sodium, potassium, carbon dioxide, chloride, BUN and creatinine.^[1] The comprehensive metabolic panel measures fourteen: the previous eight plus albumin, total protein, alkaline phosphatase, ALT, AST and bilirubin.^[2] The lipid panel measures total cholesterol, LDL, HDL and triglycerides.^[4] A Mexican “24” is usually, in practice, a comprehensive metabolic panel plus lipids and some electrolytes; a “35” is the same plus extras.

What each block answers

Glucose

Fasting glucose is a snapshot of blood sugar that morning. The US reference considers up to 99 mg/dL normal, 100 to 125 prediabetes and 126 or above diabetes.^[7] If what interests you is the average rather than the snapshot, HbA1c is not part of the chemistry panel: it is ordered separately and needs no fasting.^[7] If your glucose already came out high, this text explains what to record.

Kidney: urea, BUN, creatinine and uric acid

Creatinine and BUN are the two kidney markers carried by both the basic panel^[1] and the comprehensive one,^[2] and from creatinine the lab or the doctor calculates the filtration rate (eGFR). Urea and BUN measure the same thing expressed two ways; having both is not double information, it is the same datum repeated. To read a high creatinine, here; for uric acid, here.

Lipids

Total cholesterol, LDL, HDL and triglycerides answer a single question: how much cardiovascular risk blood fats contribute.^[4] The US reference marks as desirable a total below 200 mg/dL, an LDL below 100 and a non-HDL below 130, and considers an HDL below 40 in men and 50 in women low.^[4] To read it calmly: high cholesterol and high triglycerides.

Liver

ALT, AST, alkaline phosphatase and GGT are enzymes; bilirubin is the residue of old red blood cells that the liver removes; albumin and total protein measure what the liver makes.^[3] Two honest caveats from the source itself: these markers alone usually cannot diagnose a specific disease, and a high value is not always from the liver: alkaline phosphatase, for example, also rises because of bone.^[3]

Electrolytes

Sodium, potassium, chloride, calcium and carbon dioxide are part of the basic panel;^[1] phosphorus and magnesium are added in the long versions. They answer whether fluids and salts are in balance, and they are the ones that move most with vomiting, diarrhoea and some medicines.

The extras of the 35

Iron, LDH, amylase, lipase and CK are markers ordered for a specific reason: a suspicion about the pancreas, the muscle or circulating iron. LDH, for example, is found in almost all tissues of the body, not only the liver,^[3] and without a specific reason, they are usually surplus.

Which to order depending on the question

The right version depends on why it is ordered, and your doctor defines that. As a guide:

• Annual check-up with nothing pending. A basic panel (glucose, kidney, electrolytes) plus a full lipid profile covers what is used for screening: the metabolic panel is ordered as part of a routine check-up,^[2] and the US reference suggests a lipid profile every 5 years between ages 20 and 65, and every 1 to 2 years in men aged 45 to 65 and women aged 55 to 65.^[4]
• Glucose follow-up. Fasting glucose and HbA1c, and little else. With prediabetes it is repeated every year; with normal results, every 3 years.^[7]
• Lipid follow-up. Full profile (total, LDL, HDL, triglycerides, non-HDL), repeated under the same conditions as last time.
• Medicines that need monitoring. The comprehensive panel is ordered when the doctor wants to know whether the liver or kidneys are being affected by a treatment,^[2] and liver markers are used to monitor medicines that can harm it.^[3]
• Symptoms. Nausea, poor appetite, tiredness, swelling, dark urine: these are reasons the liver panel is ordered,^[3] and the comprehensive panel is used to look for the cause of symptoms with many possible explanations, such as fatigue.^[2]
• Your doctor asked for a specific panel. Order that one: swapping it for “the 35” adds loose values, not answers.

Why more is not always better

The problem with “the 35 just in case” lies in how ranges are built. Reference intervals come from the results of large groups of healthy people, and it is common for a healthy person to sometimes have a result outside the range.^[5] The more markers you order, the more likely one comes out flagged without meaning anything, and each of those loose values costs: a repeat, an extra appointment, weeks of worry. A result within the range does not guarantee health either,^[5] so the long panel does not buy peace of mind; it buys numbers.

Fasting: what needs it and what does not

Fasting is not a rule for the whole panel but for some of its blocks, and it is worth knowing which so you do not repeat because of a condition that was not needed.

• Fasting glucose: yes. At least 8 hours without eating or drinking anything except sips of water.^[7] The basic panel usually asks for that same 8-hour fast.^[1]
• Lipids: not routinely. The 2016 European consensus recommends taking the lipid profile without fasting, because the changes after a habitual meal are small: triglycerides rise about 26 mg/dL and total cholesterol and LDL fall about 8.^[6] What changes is the threshold: triglycerides of 175 mg/dL or more are flagged without fasting, 150 or more with fasting, and a fasting repeat is advisable if non-fasting values exceed 440.^[6] If the panel includes glucose, you will be fasting anyway.
• Liver: the US source indicates you will probably be asked to fast 10 to 12 hours.^[3] Follow your lab’s instructions.
• What matters as much as fasting: what you ate and drank, hard exercise before the test, medicines and supplements, and having your period can affect some results.^[5] Note it next to the result, so next time is comparable.

How to read a value “slightly off”

Three things before worrying about a flagged value. First: the range on the paper belongs to that lab and that method. The Mexican clinical laboratory standard requires reference values to be printed according to the method used and the sex and age group,^[8] and US regulation requires reference intervals to be determined by the laboratory performing the test.^[9] That is why two labs can flag the same number differently, and why results from different labs are not compared without care.^[5]

Second: a value outside the range may or may not be a sign of a problem; your doctor reads it together with the rest of the panel, your symptoms and your history.^[5] Third: the trend weighs more than the point. If you have the previous result, put them side by side under the same conditions; to follow a trend, the recommendation is to use the same lab.^[5] If you do not yet know where to start reading, this guide comes first, and this text explains why the range is not your norm.

Warning signs: when you do not wait for the appointment

There are two kinds of alarm. The first comes from the lab: US regulation requires the laboratory to immediately alert whoever ordered the test when a result indicates an imminently life-threatening condition, the so-called critical or panic values.^[9] Potassium, sodium, glucose or creatinine at extremes fall into that category. The Mexican laboratory standard does not set that list,^[8] so ask your lab how they notify and whom. If they call you, do not wait for the appointment: that is the reason for the call.

The second comes from the body. Seek care now, without waiting for results, if you have:

• Yellow skin or eyes, very dark urine or pale stools.
• Severe abdominal pain or pain that does not ease, especially under the ribs or radiating to the back.
• Confusion, unusual drowsiness, marked weakness or palpitations with dizziness.
• Vomiting or diarrhoea that will not stop, or no longer urinating.
• Sudden swelling of legs, face or abdomen, especially with shortness of breath.

What to ask before ordering it

1. What do you want to know with this test? If the answer is a block (kidney, liver, lipids, glucose), you already know which version you need.
2. Which exact markers do you want? Ask for the list and compare it with the lab’s quote; the number of markers says nothing.
3. Do I need to fast, and for how many hours? It depends on the blocks, not the package.
4. What do we do with a value slightly off? Agree in advance whether to repeat, wait or consult.
5. Is the previous result useful to you? Bring the ones you have: the comparison is the datum no new panel carries.