Constant colds: which tests to take if you are sick every month

When colds become a reason for workup

Adults normally get 2–4 respiratory infections a year, more in season and around small children. If you are sick every month, each cold drags on for weeks, or every infection ends in antibiotics, that is no longer "weak immunity" in general — it is a signal to find a specific cause.

The search starts not with exotic immune panels but with a cheap basic set: most causes of frequent infections sit on the surface — iron deficiency, low vitamin D, uncontrolled blood sugar, a chronic focus of inflammation.

Step one: blood with a differential

A complete blood count with differential shows the state of immune cells directly. Few neutrophils — bacteria have it easier; few lymphocytes — viruses do. Monocyte shifts hint at smoldering inflammation, and eosinophils suggest that the monthly "cold" is actually allergic rhinitis.

Alongside sit hemoglobin and ferritin: hidden iron deficiency without anemia is a frequent finding in people who are always sick, especially women. Iron is needed not only by red cells but by immune cells as well.

Step two: deficiencies and metabolism

Vitamin D takes part in innate immunity, and deficiency in northern latitudes is a mass phenomenon from October to May. A 25(OH)D test is the only way to know your level instead of guessing at supplement doses.

Add glucose: with uncontrolled diabetes and prediabetes, infections run more often and harder. If your "colds" come with boils, slow-healing scratches, or thrush, blood sugar is checked first.

What next if the basics are clean

If the differential, ferritin, vitamin D, and glucose are fine but infections continue, the doctor looks for a chronic focus — sinusitis, tonsillitis, adenoids. A permanently irritated focus produces exactly the picture of being sick every month.

And only when foci, deficiencies, and differential shifts are excluded does deeper immune diagnostics make sense — immunoglobulins and lymphocyte subpopulations as ordered by an immunologist. Starting with those expensive tests is unnecessary.

The basic set for frequent colds

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